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INTRODUCTION TO BIOMEDICAL
INSTRUMENTATION
The Technology of Patient Care
This book is designed to introduce the reader to the fundamental
information necessary for work in the clinical setting, supporting the
technology used in patient care. Beginning biomedical equipmenttechnologists can use this book to obtain a working vocabulary and
elementary knowledge of the industry. Content is presented through
the inclusion of a wide variety of medical instrumentation, with an
emphasis on generic devices and classi fications; individual manufac-
turers are explained only when the market is dominated by a par-ticular unit. This book is designed for the reader with a fundamental
understanding of anatomy, physiology, and medical terminology
appropriate for their role in the health care field and assumes the
reader ’s understanding of electronic concepts, including voltage,
current, resistance, impedance, analog and digital signals, and sensors.
The material covered in this book will assist the reader in the devel-opment of his or her role as a knowledgeable and effective member of
the patient care team.
Barbara L. Christe is Associate Professor and Program Director of
Biomedical Engineering Technology at Indiana University Purdue
University Indianapolis.

INTRODUCTION
TO BIOMEDICAL
INSTRUMENTATION
The Technology of Patient Care
Barbara L. Christe
Indiana University Purdue University
Indianapolis

CAMBRIDGE UNIVERSITY PRESS
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São Paulo, Delhi, Dubai, Tokyo
Cambridge University Press
The Edinburgh Building, Cambridge CB2 8RU, UK
First published in print format
ISBN-13 978-0-521-51512-2ISBN-13 978-0-511-65046-8© Cambridge University Press 2009
2009Information on this title: www.cambrid ge.org/[anonimizat]
This publication is in copyright. Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any partmay take place without the written permission of Cambridge University Press.
Cambridge University Press has no responsibility for the persistence or accuracy of urls for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.Published in the United States of America by Cambridge University Press, New York
www.cambridge.org
eBook (NetLibrar y)
Hardback

Contents
Preface page vii
1BMET as a career ………………………….. 1
2Patient safety . ………………………….. 19
3In the workplace ………………………… 39
4Electrodes, sensors, signals, and noise ……………. 53
5The heart ……………………………… 69
6Cardiac assist devices ………………………. 87
7Blood pressure …………………………. 103
8Respiration and respiratory therapy …………….. 113
9The brain and its activity ……………………. 127
10The intensive care unit …………………….. 139
11The operating room ………………………. 155
12Imaging ……………………………… 177
13Clinical laboratory equipment. ……………….. 193
14Intravenous pumps and other pumps ……………. 205
15Miscellaneous devices and topics ………………. 213
Index 223
v

Preface
This book serves readers who would like to explore medical
equipment that is used in the clinical setting. It offers an overviewof the fundamental information necessary for work in the field.
The material is designed to provide a working vocabulary andelementary knowledge of the medical equipment involved in the
treatment of patients. Readers are encouraged to become know-ledgeable and effective members of the patient care team, buildingon the information in this book as a foundation for further study.
Readers should have a fundamental understanding of anat-
omy, physiology, and medical terminology appropriate for their role in
the health care field. Readers are assumed to have a fundamental
knowledge of basic electronics concepts including voltage, current,
resistance, impedance, analog and digital signals, and sensors.Readers without this background may have to explore terms andconcepts referenced in the text.
There is a vital connection between technology and the care
of patients. In many cases, health care workers depend on tech-nology to administer care or treatment or to make a diagnosis.This book helps readers understand how technology is tightlywoven into patient care. The role of technical support for themedical team is, therefore, essential in the delivery of effective
medical care.
vii

The section of each chapter entitled “For Further Exploration ”
encourages readers to use the Internet to obtain in-depth infor-
mation about a topic. Questions are designed to push the reader to
integrate concepts using external sources. Answers are not specif-
ically available within the chapters. While Wikipedia (http://www.wikipedia.com) may not be an academically authoritative source, itis often an excellent starting point for research. Research exercisesencourage one of the most important skills of a successful bio-medical equipment technician (BMET) –investigation of topics
that are not well understood. In the clinical setting, it is impossibleto be an expert about all technology and aspects of patient care.The ability to effectively search for information is vital.
All photographs (unless otherwise noted) are by Valerie
Shiver.
Special appreciation is extended to my collegiate mentors,
Dean Jeutter and Joe Bronzino. I am in debt to my colleagues inhigher education, Steve Yelton, Roger Bowles, Elaine Cooney,and Ken Reid, as well as those who have supported me in theclinical setting, including Dave Francouer, Karen Waninger, KellyVandewalker, Steve Erdosy, and Bob Pennington. Without theirencouragement, this book could not have been written. Lastly, to
my parents and children, I am deeply grateful for their love and
understanding.
Those who support the technology used in patient care are a
dedicated and sel fless part of the workforce. They are part of the
medical team and have excellent technical skills. Most import-antly, BMETs work closely with staff to ensure safe and effective
patient care. May this book be the beginning of a transformation
that increases career awareness, improves enrollment in trainingprograms, and expands the recognition BMETs deserve.viii Preface

INTRODUCTION TO BIOMEDICAL
INSTRUMENTATION
The Technology of Patient Care

1
BMET as a career
LEARNING OBJECTIVES
1.describe the role of a BMET
2.list and describe potential employers of a BMET
3.characterize field service representatives
4.list and describe the many job functions of a BMET
5.list and characterize the certi fication requirements
6.list and describe related professional societies and journals
1

What is the name of this career?
There are many de finitions for what the letters BMET stand for –
biomedical equipment technician, b iomedical electronics technol-
ogy, medical maintenance, biomedical engineering technologist,
biomedical engineer, medical engi neer, medical equipment repair
technician, and many more. In general, it is the title for someonewho works in the clinical setting and supports the equipmentinvolved in patient care.
At different hospitals, staff may have a wide variety of titles.
Staff may be called the “biomeds, ”“clinical engineers, ”or the
“equipment guys. ”In some hospitals, BMETs may be responsible
for everything from printers to computers to DVD players in therooms of patients. In some hospitals, BMETs work for themaintenance departments and wear janitor ’s jumpsuits. Other
hospitals hire a wide range of technical staff who wear lab coats,monogrammed polo shirts, or dress shirts.
Because there is so little uniformity, it can be dif ficult for the
career field to get the recognition it deserves. Some basic facts are
true for most BMETs.
What do BMETs do?
Most BMETs perform several main categories of job function. Ingeneral, BMETs are responsible for the support of the technologyused in health care. This support assures the safe use of equipment
and the best possible patient care. BMETs work closely with
medical staff to make sure technology is used safely and effectively.
Ultimately, the customer of BMET services is the patient,
although many times the patient and BMET are not in the same2 Introduction to Biomedical Instrumentation

place at the same time. Most experienced BMETs de fine the best
BMET as one who thinks of each patient as a relative or loved
one. The care and attention one would expect under these cir-
cumstances should drive a BMET ’s job performance.
Who employs BMETs?
Generally, there are three groups of employers of BMETs: hos-pitals, outside service providers, and the manufacturers themselves.
Those who work for the hospital directly or an outside serviceorganization (OSA) or independent service organization (ISO) mayappear the same to clinical staff. Some employment issues (bene-fits, etc.) could be different, but the work-related duties are likely to
be similar. Often, when employees work for a manufacturer they
are identi fied as field service representatives or FSRs.
Hospital-employed BMETs generally have the following
responsibilities:
▶Equipment repair and troubleshooting –BMETs fix
equipment that is not functioning as expected. This repairmay or may not be done “in the shop. ”BMETs may need to
retrieve equipment that has a “broke ”sign attached to it, or they
may be called to the operating room during a case. Figure 1.1
shows a BMET working on a physiological monitor at herworkstation in the clinical engineering shop of the hospital.
▶Preventative maintenance (PM) –BMETs routinely verify
the performance of almost all equipment. This involvesevaluating the performance of every aspect of a device andchecking or replacing parts to ensure consistent, dependableservice. PM may include conducting calibrations andBMET as a career 3

safety checks as well as removing the “white dust ”that comes
from bed linens, a task that occupies a great deal of the
fledgling BMET ’s time. Performing preventive maintenance is
a great way to learn about all the features of an instrument,and the experience can assist a BMET in futuretroubleshooting. This type of activity is sometimes calledperformance assurance . Figure 1.2 shows a BMET performing
PM on a ventilator.
Figure 1.1. A BMET works in the shop on a physiological monitor.4 Introduction to Biomedical Instrumentation

Figure 1.2. A BMET calibrates a ventilator.BMET as a career 5

▶Staff support –BMETs provide both formal and informal
equipment instruction to many groups including the users
of equipment and other BMETs. BMETs may arrange and
lead an in-service meeting during a staff meeting to introduce
a new device and train staff. BMETs also work one-on-one
with a staff member. Excellent customer service is vital toeffective job performance.
▶Pre-purchase evaluation –As new equipment (new models
or entirely new devices) is considered for purchase, many
BMETs are involved in the selection decisions, usually working
very closely with the medical staff. As medical technologybecomes interwoven with other medical equipment in thehospital, the cross-departmental interactions often fall toBMETs.
▶Incident investigation –When there are problems with
equipment, experienced BMETs are often part of the teamthat evaluates issues surrounding a malfunction.
▶Incoming testing –When new devices arrive at the hospital,
BMETs must verify that every aspect of every piece ofequipment functions properly.
▶Adaptations/modi fications –BMETs are occasionally asked
to modify equipment to better medically serve clinical staff aswell as better serve a patient with restrictions or limitations.
▶Departmental development/training classes –Departments
have meetings and other activities that must be documented.Documentation of activities is a required departmentalactivity. Accreditation bodies have a policy that basically
concludes: “if it is not written down, it did not happen. ”In
addition, BMETs are often expected to participate in
additional training, which is usually device speci fica n d
often offered by the manufacturer.6 Introduction to Biomedical Instrumentation

▶Updates –When manufacturers change or update equipment
(for example, software) the BMET installs or makes the
necessary changes.
▶Safety board –BMETs help to set policies and investigate
problems, especially regarding hospital process ef ficiency and
staff training. In addition, plans for emergencies includemedical equipment, and BMETs contribute to these disasterplans.
Non-hospital-employed BMETs take on a number of the
previous responsibilities in addition to some of the followingfunctions:
▶Telephone support –Some BMETs answer phone lines to
assist users of equipment as well as technicians who areattempting to make a repair.
▶Sales –Some BMETs work for a manufacturer, outside
service organization, or repair depot as a salesperson.
▶New equipment design –Some BMETs work for a
manufacturer and design new devices.
In general, most hospital-based BMETs work “hospital ”hours:
7A.M. to 3:30 P.M. (or something like that) Monday through
Friday. While some institutions do have shifts on weekends, mostshops do not staff nights or weekends. Policies for “on-call ”
coverage vary, although most hospitals easily deal with problems“off hours” with minimal weekend and night trips back to work.
Table 1.1 shows the standardized defi nitions for people who
support medical equipment technology. Levels have been iden-tified based on years of experience, and this table also explains the
higher education requirements that are most common (althoughnot absolutely required).BMET as a career 7

TABLE 1.1. AAMI job descriptions
BMET I –An entry-level or junior biomedical equipment technician (BMET). Works under
close supervision. Performs skilled work on preventive maintenance, repair, safety testing, and
recording functional test data. Not certi fied. Usually has less than four years of experience.
BMET II –A BMET who usually has a two-year degree or higher. Has good knowledge
of schematics and works independently on repairs, safety testing, and preventive
maintenance (PM). Maintains records, writes reports, and coordinates outside repairs.
Average experience is eight years.
BMET III –A highly experienced or specialized BMET usually having an AS (two-year)
degree or higher. Has substantial experience and may be certi fied (CBET). Does highly
skilled work of considerable dif ficulty. Has comprehensive knowledge of practices,
procedures, and types of equipment. Average experience is 12 years.Equipment Specialist –A highly specialized BMET having special training or
equivalent experience in lab equipment (LES) or radiology equipment (RES). Usually
has an AS (two-year) degree or higher. Performs highly skilled work of considerabledifficulty and may hold certi fication as CLES or CRES.
BMET Supervisor –A BMET who supervises others. Has a signi ficant amount of
training, education, or equivalent experience. Most have a BS (four-year) degree orhigher. Schedules and assigns work to subordinates, but also continues to do highlyskilled repairs. Has comprehensive knowledge of practices, procedures, and types ofequipment. Average experience is 13 years.
Clinical Engineer –A graduate engineer holding a BS, MS, or PhD. Performs
engineering-level work of considerable diffi culty. Has the ability to modify devices and
do analysis of devices and systems.Clinical Engineering Supervisor –A clinical engineer who supervises BMET/peer/
subordinate clinical engineers; may also supervise equipment specialists. Usually
degreed engineer at BA, MS, or PhD level. Average experience is 21 years.
Director/Department Manager –Most are educated or experienced as clinical engineers or
BMETs, but others may be trained in administration or business or have extensive health
care supervisory experience. Most have a signi ficant amount of technical or management
experience and the skills to select high-tech equipment and acquire, maintain, and repairequipment. Supervises BMETs, clinical engineers, and support personnel. May also be thechief technology of fic e ro rv i c ep r e s i d e n tf o rh e a l t hc a r et e c h n o l o g y .
IT Technologist/Technician –An IT technologist/technician manages projects in the
areas of system administration, software development, and network security andprovides direct technical support in at least one of these areas.
Source: Biomedical Instrumentation and Technology , January 2008, p. 26. Reprinted with permission
from Biomedical Instrumentation & Technology , a peer-reviewed journal by the Association for
the Advancement of Medical Instrumentation. Visit www.aami.org to learn more about AAMI or
to view BI&T ’s current issue.

Field service representatives
Field service representatives (FSRs) are generally employed by the
manufacturer of a medical device or technology. This person
represents the company by servicing or supporting (training, forexample) a particular device or group of devices at the clinicalsite. Sometimes these BMETs are called field service engineers,
equipment specialists, or customer engineers.
In general, field service representatives perform many of the
job functions of general BMETs. The proportion of the timespent on the various facets of the job shifts when FSRs focus onone type or group of equipment. In addition, some FSRs are veryspecialized as trainers or do mainly repairs and therefore have avery narrow range of duties.
Generally, FSRs are commonly used in such areas as radiology
(imaging), clinical laboratory, anesthesia, LASERs, and operatingroom equipment, to name a few. Most common is imaging andclinical lab since they involve very complex, very expensive equip-ment that requires in-depth (weeks or months of) training. It is asignificant financial and personnel commitment for individual
institutions to train people to support a single device (or a few)
that one hospital owns. By spreading the technical skills of an FSR
over several hospitals, support expenses to the institution may beless. Or, contracting for service may be the only option an insti-tution has to provide a skilled technician who can support thedevice (irrespective of cost).
Most field service representatives work under a service con-
tract purchased by a clinical facility. Some manufacturers requirethat service only be performed by their own FSRs. In addition,service contracts can be ef ficient for the institution because a
highly trained person will respond quickly. This may be especiallyBMET as a career 9

true when downtime of a particular device adversely affects
patient care.
There are generally two types of service contracts. A full
service contract speci fies that an FSR will respond within a cer-
tain period of time and repair the equipment with no additionalcosts. The exact financial arrangement and details are usually
negotiated. Another category of service contract provides lesscomprehensive service. For example, the contract may be “time
and materials ”–this allows a hospital to have access to an FSR
and still pay them an hourly rate (usually with a minimumnumber of hours) as well as the cost of the parts. Some servicecontracts allow in-house BMETs to look at the device to try toidentify any simple issues; this first-response technique may also
include phone technical support for the in-house BMET.
Many FSRs travel between clinical sites. In some territories,
this travel may be minutes, in larger states, the amount of time onthe road can be hours. The territory that an FSR covers may alsoimpact the number of nights that are not spent at home. ManyFSRs work out of their car, stocking parts in the trunk andcompleting paperwork in hotel rooms or at home. Many FSRs areon call 24 x 7 and may be required to stay at a site until a repair is
complete. Overtime is relatively common, and their schedule may
not be very predictable. To compensate BMETs for these chal-lenges, the salaries offered to field service reps are usually very good
(and often higher than hospital-based BMETs). Bene fits often
include a company car and other travel expenses. There may beincentives and bonuses available. Long-term salary surveys show
large salary improvements for those BMETs who specialize in
areas such as imaging and the clinical lab.
Many BMET students express an interest in specialization,
mainly because of the high salary potential. It may be diffi cult to10 Introduction to Biomedical Instrumentation

secure a position as an FSR without some BMET experience. An
FSR is the only person at a site to solve a problem. Very fewcompanies will consider hiring a person who has never worked as
a BMET and never been in the clinical setting (except perhaps
during their internship) to shoulder the heavy responsibility ofexpensive equipment and corporate reputation. Willingness torelocate may also be required. Lastly, in addition to excellenttechnical skills, FSRs must have excellent customer service skills.The ability to communicate with the medical staff, especially
when there are dif ficulties and delays, can be vital to the rela-
tionship between the manufacturer and the clinical site. Per-
sonality and professionalism will be absolutely required to locatea position as an FSR.
Is there a national license or certification?
Unlike nursing and other medical professions, there is nolicensure required to be a BMET. Optional national and inter-national certi fications are available; however, employers vary as to
the emphasis certi fication receives.
The most common certi fication is offered by the International
Certification Commission. The process and procedures are over-
seen by AAMI (Association for the Advancement of MedicalInstrumentation). This group offers three types of certi fication,
which are indenti fied in Table 1.2. The first step to obtain certi fi-
cation is to take a national exam (there is a separate exam for each
of the three types of certi fication). Applicants with an associate ’s
degree in BMET can take the CBET exam as a candidate. Appli-
cants who have this 2-year degree and 2 years of work experience
in the field can take the exam for full certi fication status.BMET as a career 11

Requirements for each of the other types of exams are available by
visiting the AAMI Web site. There is a fee to take this exam, butmost employers will reimburse the cost if you are successfully
certified.
Details about the exam are located at http://www.aami.org/
certification/about.html.
There are five sections of the CBET exam:
▶Anatomy and Physiology
▶Safety in the Health Care Facility
▶Fundamentals of Electronics
▶Medical Equipment Function and Operation
▶Medical Equipment Problem Solving
Most successful candidates study before the test.
Less common is certi fication obtained through the Elec-
tronics Technicians Association –International (ETA-I), which
offers both a student and a professional certi fication or The
International Society of Certi fied Electronics Technicians
(ISCET). Both organizations offer Certi fied Electronics Techni-
cian (CET) exams in the biomedical field.
Certification can improve pay rates but generally not a great
deal. It is not required for employment by any government body.
Very few employers require certification for employment butmany employers recommend it.TABLE 1.2. Types of ICC certi fication
Type of certi fication Position
CBET Biomedical equipment technicians
CRES Radiology equipment specialists
CLES Laboratory equipment specialists12 Introduction to Biomedical Instrumentation

What regulatory agencies govern the work of BMETs?
Numerous governing bodies and associations guide the use of
equipment in medical care. Many groups do not regulate using
laws but rather offer guidelines and validation of compliance withstandards of best practice. All hospitals are legally regulated by theboard of health for a speci fic municipality. However, most speci fic
guidelines do not come from state and local legislatures. The mostprominent agency is The Joint Commission (previously known as
The Joint Commission on Accreditation of Healthcare Organiza-
tions, JCAHO). It is an independent, not-for-pro fit organization
that does not speci fically “regulate ”hospitals but offers voluntary
accreditation. With this accreditation, a hospital is eligible forMedicaid and Medicare payments. While technically optional,almost all hospitals are inspected by The Joint Commission in
order to be reimbursed for patients covered by Medicare and
Medicaid. The Joint Commission guides many hospital activities,not just the support of technology. Other agencies and associ-ations include the National Fire Protection Association (NFPA),Compressed Gas Association (CGA), College of American Pathol-ogy (CAP), Occupational Health and Safety Association (OSHA),
the Laser Safety Institute (LSA), and the Association for the
Advancement of Medical Instrumentation.
What are some ways that BMETs stay connected?
▶Subscribe to 24 x 7, afreemagazine designed for BMETs.
Visit http://www.24x7mag.com to subscribe.
▶Subscribe to Medical Dealer, afreemagazine that contains
articles for biomedical technicians. To subscribe, visit theWeb site at www.mdpublishing.com.BMET as a career 13

▶Join Biomedtalk-L. Biomedtalk is an email listserv that
allows BMETs to communicate about a wide variety of
topics, some very technical, some very humorous. There is a
small fee to subscribe. Visit www.bmetsonline.org.
▶Join the Association for the Advancement of Medical
Instrumentation . AAMI has several excellent publications as
well as a large annual conference. For students enrolled in at
least 12 credit hours, the cost is extremely low. The Web sitefor the association is http://www.aami.org.
▶Join your local society . Many areas of the United States have
organizations. A list of regional groups is available on the AAMIWeb site http://www.aami.org/re sources/links/biomed.html.
▶META (Medical Equipment and Technology Association) is
a newer BMET association that has some good resources. Itssite is http://www.mymeta.org/.
Note that BMET is sometimes confused with biomedical engin-
eering (BME), which is not very closely related to the work of
BMETs. Most biomedical engineers are focused more on theresearch than on the support of existing devices and technologies.Many biomedical engineers are examining issues at a cellular leveland do not have a foundation in electronics. You can visit theBiomedical Engineering Society Web site at http://www.bmes.org
to see the differences clearly. A point of great confusion occurs
when hospitals and societies label BMETs as biomedical engineers.
STUDY QUESTIONS
1..Write a brief want ad you might see for a BMET entry-level
position. Include typical duties and quali fications.14 Introduction to Biomedical Instrumentation

2..Where does a BMET usually work? Who are typical employers?
3..What is an in-service meeting? Who would attend?
4..What is done during a PM? Why are they bene ficial?
5..Describe a typical day for hospital-based, entry-level BMETs.
What would the BMETs wear? How might they spend theirtime? Where in the hospital would they be doing theseactivities?
6..Make a list of the advantages and disadvantages of field
service work.
7..Define and describe certi fication. Is it voluntary? Why might a
BMET become certi fied?
8..Being inspected by The Joint Commission is technicallyoptional but why is it important to so many facilities?
9..Make a list of some of the groups that you might considerjoining as part of your career. List some of the bene fits of
joining associations and societies.
FOR FURTHER EXPLORATION
1..The lack of career awareness can be a signi ficant hurdle.
Visit the government ’sOccupational Outlook Handbook (from the
U.S. Department of Labor) and search for “medical equipment
repairers. ”Summarize the information presented. Does the
information look accurate for the positions in your area?
2..Visit AAMI ’s BMET career Web site at http://www.aami.org/
resources/BMET. Summarize the information presented.
3..Watch a video made about the BMET field. It is located at
http://www.learnmoreindiana.org/careers/exploring/Pages/CareerPro files.aspx?VID=7&SOC=49906200&LID=0&RFP=
1&RBP=557. Summarize the information presented.BMET as a career 15

4..In what year was nursing founded? Now, consider that
technology was not used in health care until the 1970s.BMETs did not exist prior to the introduction of technology
into patient care. What kind of impact has the relatively short
history of biomedical instrumentation had on the prestige andrecognition of BMETs within the hospital? For example, canyou understand how space allocation in a hospital is in fluenced
by“who got there first ”? Use the Internet to collect references
to substantiate your answers.
5..As i g n i ficant rise in BMET career awareness occurred with
an article written by Ralph Nader in Ladies Home Journal in
March 1971; it claimed that there were a large number ofhospital electrocutions each year. Search the Internet for thisinfamous article and summarize it. Evaluate the prestige and
style of the article. Discuss the impact of the article on the
career today.
6..What hospital employees make up a hospital safety committee?
Why should BMETs be on this committee? What role do theyplay in hospital safety and emergency planning?
7..How can BMETs promote good communication with staffabout devices that do not work? Design and propose
communication methods, including feedback from BMETs,
that would enhance the relationship between BMETs and thestaff who use the equipment.
8..Visit the Web site for the journal 24 x 7 . Look in the archives for
an article that interests you. Summarize the article. Include areflection on how this information might have an impact on
your career when you are working in the field.
9..Explore generic Web sites that post employment ads, such asmonster.com. Search for positions that are related to BMETwork. Summarize the number and type of positions you find.16 Introduction to Biomedical Instrumentation

Now search Web sites that post positions for BMETs such as
AAMI ’s job postings at http://www.aami.org/CareerCenter/
SearchJobPostings.cfm. Describe how the opportunities are
different. Visit major BMET employers such as http://www
.philips.com (search in “Healthcare ”)a n dh t t p : / / w w w
.aramarkhealthcare.com and explore the employment sections.
Summarize a position that you find that seems appealing to you.BMET as a career 17

2
Patient safety
LEARNING OBJECTIVES
1.define the types of currents related to the human body
2.identify the amount of current related to physical sensation,
pain, injury, and death
3.define microshock and macroshock
4.define the hazardous currents in clinical electrical
equipment
5.identify the basic AAMI recommended limits for currents in
permanently wired devices and portable ones
6.identify NFPA 99 code
7.identify electrical receptacle requirements in a hospital (wiringand testing)
8.define GFCI and LIM and identify the regulations set for their
performance in the clinical environment
9.define the patient care area
10.identify the maximum duration of power interruption before
emergency power is provided
11.know NFPA 99 code requirements for extension cords and
outlet strips
12.identify the code requirement for the ground-to-chassisresistance measurement
19

13.understand how NFPA 99 can be used to obtain maintenance
manuals for equipment
14.identify the applicability of Life Safety Code 101
Introduction
The most important responsibility of BMETs relates to patient
safety. Ensuring the safe use of technology is a vital role of theBMET as part of the medical care team. Understanding thehuman body and its reaction to externally applied voltage and/orcurrent is vital to patient safety.
Electrical shock
An injury related to electrical shock may occur in any environ-ment, but there is a higher potential for electrical injury in thehospital because of the direct contact of patient or caregiver andequipment. In addition, there are a great many devices that maybe associated with one patient. The sensations or characteristicsymptoms of various levels of electrical current are described in
the following paragraphs and summarized in Table 2.1. The
effects of electrical currents on the human body and tissue mayrange from a tingling sensation to tissue burns and heartfibrillation leading to death.
Electrical energy has three general effects on the body:
1..Resistive heating of tissue
2..Electrical stimulation of the tissue (nerve and muscle)
3..Electrochemical burns (for direct current)20 Introduction to Biomedical Instrumentation

When the human body is exposed to current, the reactions can be
grouped based on the quantity of current. There are six currentcategories:
Threshold Current (1–5 milliamperes (mA)): This is the level of
current required to perceive the feeling of current. A slight fuzzy
feeling or tingling sensation is common at this current strength.
Pain Current (5–8 mA): This current level will produce a pain
response, which may feel like a sharp bite.Let Go Current (8–20 mA): This current level results in involun-
tary muscle contraction. Nerves and muscles are strongly stimu-
lated, resulting in pain and fatigue. At the low end of let go currentis the maximum amount of current from which a person can moveaway voluntarily (about 9.5 mA). At these levels, injuries may resultTABLE 2.1. Human detection of current
Current
description Current (mA) Physiological effect
Threshold 1 –5 Tingling sensation
Pain 5 –8 Intense or painful sensation
Let go 8 –20 Threshold of involuntary
muscle contraction
Paralysis >20 Respiratory paralysis and pain
Fibrillation 80 –1,000 Ventricular and heart
fibrillation
Defibrillation 1,000 –10,000 Sustained myocardial
contraction and possible tissue
burns
Note: These values will vary based on the person ’s gender, size and weight,
skin moisture content, and pain tolerance levels.Patient safety 21

from the instinct to pull away, for example, arm dislocation or
broken bones from falls.
Paralysis Current (>20 mA): At levels greater than about 20 mA,
the muscles lose their ability to relax. This includes the muscles
involved in breathing. The breathing pattern can no longer be
maintained and results in respiratory paralysis. Respiratory paral-
y s i sc a nr e s u l ti nd e a t h .
Fibrillation (80–1,000 mA): At levels between 80 and 1,000 mA, the
heart goes into fibrillation. Fibrillation is the unsynchronized
contraction of the muscle cells within the heart. During fibrillation,
the heart is ineffective in pumping blood to the body. Heart fib-
rillation will result in death.Defibrillation (1,000 –10,000 mA): The delivery of electrical energy
to the fibrillating heart is called de fibrillation. A large current
delivered by paddles at the skin, through muscle and bone, can
resynchronize all of the cardiac muscles. Then, coordinated elec-trical generation can return to the heart. During open-heart sur-gery, spoon-shaped paddles can deliver much lower currentsdirectly to the heart to induce fibrillation (to perform bypass
surgery, for example) and then de fibrillate the heart after the
procedure is complete.
Researchers at Massachusetts Institute of Technology would
like these current ranges rede fined. One reason they would like to
see the change is the vast differences among people in size andperception of pain. Because there is such a great variance fromperson to person, keep in mind that the current ranges listed hereare only guidelines and approximations.22 Introduction to Biomedical Instrumentation

The electrical shock situations described in Table 2.1 are
identi fied by the term macroshock. Macroshock is a physiologic
response resulting from electrical current in contact with the skin
of the body. Macroshock can occur when a person makes an
electrical connection with two parts of the body (arms, forexample) or a person is connected to “earth ground ”(a lower
potential area) and makes an electrical connection with one pointof an energized source.
The skin of the body provides some protection from electrical
hazards because of the skin ’s resistive properties. Dry, unbroken
skin acts as an insulator. In the hospital environment, a patientmay be especially susceptible to small electrical currents becausethe skin may be wet (patient fluids) from wounds.
One patient may have a fluid-filled catheter, and another may
have an electrical wire in direct contact with her heart. If this
pathway is used to conduct electricity directly to the heart, the
patient can experience microshock. Microshock is a physiological
response resulting from electri cal current applied to the heart.
Microshock currents are often tiny, so they are measured inmicroamperes ( μA). Because there is a direct connection to the heart,
even these small currents can be large enough to cause fibrillation of
the heart. Be aware that very little can be done within a power systemto protect against microshock. Isolated power, ground fault circuitinterrupters, line isolation monitors, and other safety precautionsdo not protect the heart directly from these lowcurrent levels.
Leakage currents
All electronic devices have natu rally occurring unintended cur-
rents within them. These are not due to any faults in the devices;Patient safety 23

they are simply present. Alldevices have leakage current. For
medical devices, BMETs categorize and measure these leakage
currents.
Four categories of leakage currents are measured and have
recommended safe limits. The categories are determined by themethod through which a person might come in contact withthe current or the device. The types of currents are:
▶Earth leakage current (also called earth risk current)i s
the current that flows from the power supply of the
device, across the insulation of the device, and throughthe ground in the power cord (three-prong power cord).
▶Enclosure leakage current (also called enclosure risk current
and touch/chassis current, chassis leakage current ) is the current
that would flow through a person if he touched any part of a
device. The person could then form a connection to earthground so this current is measured between the chassis andthe earth ground.
▶Patient leakage current (patient risk current ) is the current
thatflows between the parts of a device that are in normal
contact with the patient such as patient leads (on the skin orunder the skin) and the earth ground.
▶Patient auxiliary current is the current that can
flow between two separate patient circuits or connections,
like two different electrodes that both connect to the
patient.
But what is leakage current and where does it come from?
Leakage current is best de fined as the small current that flows
from the components of a device to the metal chassis. This isnatural and is a result of wiring and components. It can be24 Introduction to Biomedical Instrumentation

either resistive or capacitive. Resistive leakage current comes
from the resistance of the insulation surrounding power wires
and transformer windings. Res istive leakage current is much
smaller than capacitive leakage current. Capacitive leakage
current forms between two oppositely charged surfaces, such as
between a wire and a chassis case or between two wires, one hot,one neutral. A capacitive current is formed between the twosurfaces and tends to stray from the intended currentpath. Adding a safety ground wire is a method to reduce
excessive leakage current. The th ird wire acts to divert the stray
or leakage current away from th e chassis (which the patient or
caregiver may come in contact with) and to the intended circuit
ground in the case of a short between a hot wire and a chassisground.
Device currents are identi fied in two circumstances: when
the device is working properly and when there is a fault. Thefault current is the current that flows when the device
is broken, the worst-case-scenario condition. The fault currentis the maximum possible current flow from a device to
ground or a person or another metal object. Types of faultsoccur when
▶The ground is not connected.
▶Each barrier of a double-insulated instrument is short-circuited.
▶A supply conductor (hot or neutral) is not connected.
▶Hot and neutral are reversed.
▶A single component that can produce a hazardous currentfails.
▶Line voltage is applied to an input or output part or chassis(for ungrounded equipment).Patient safety 25

▶Line voltage is applied to a patient part (for isolated patient
connections).
Standards
The Association for the Advancement of Medical Instrumen-tation and the National Fire Protection Association establishrecommendations for the limits for leakage currents for
medical devices. There are diffe rent limits for the two types of
equipment connections. Current limits are higher for fixed
equipment orhard-wired equipment, devices that are per-
manently wired to the electric al power supply (for example,
imaging devices), than they are for devices that are “plugged in”
using a power cord. Even though we use the term “fixed
equipment,” it should not be confused with equipment that has
been repaired.
Summary of important values
For fixed equipment , earth leakage current is tested prior to
installation when the equipment is temporarily insulated from
ground. The leakage current from the device frame to ground of
permanently wired equipment installed in general or criticalpatient care areas cannot exceed 5.0 mA (with groundsdisconnected). For portable equ ipment, earth leakage current
cannot exceed 300 μA( r a i s e df r o m1 0 0 μA in 1993).
When multiple devices are connected and more than one power
cord supplies power (for example, equipment located on a cart),the devices should be separated into groups according to their26 Introduction to Biomedical Instrumentation

power supply cord, and the leakage current should be measured
independently for each group as an assembly.
NFPA 99
The National Fire Protection Association established a code in1984 “to minimize the hazards of fire, explosion, and electricity in
health care facilities providing services to human beings. ”Code 99
applies to health care and the technology used within the clinical
setting. The entire code is available online at http://www.nfpa.org.
Some states have adopted NFPA 99 as state law. When statesadopt these standards as law, they become absolute legalrequirements. Currently, the American Society for HealthcareEngineering is working to rewrite this code. More information isavailable at http://www.ashe.org, click on “Codes and Standards. ”
Standard regulatory definitions
Anesthetizing locations: An area of the facility designated to be
used for the administration of non flammable inhalation anes-
thetic agents. (Flammable anesthetics, such as ether, are nolonger used in this country. There were many precautions andregulations when flammable anesthetics were used.)
Fault current: A current due to an accidental connection
between the energized (hot) line and ground.
Grounding system: A system of conductors that provides a low-
impedance return path for leakage and fault currents.Patient safety 27

GFCI (ground fault circuit interrupter): A device that will interrupt
(this means “break ”or“stop power ”) the electric circuit to a load
when the fault current to ground exceeds a speci fied value. GFCIs
must activate when fault current to ground is 6 mA or greater.
Isolated power: A system that uses a transformer to produce
isolated power and a line isolation monitor. The electrical grounds
of the system are connected (on both the hospital and isolatedside). It is the power that is isolated (hot and neutral).
Isolation transformer: A transformer used to electrically isolate
two power systems.
LIM (line isolation monitor): A line isolation monitor is an in-
line, isolated-power test instrument designed to continually
check the impedance from each line of an isolated circuit to
ground. It contains a built-in test circuit to test the alarmwithout adding additional leakage current. The line isolationmonitor provides a warning (usually a loud buzz or other noise)when a single fault occurs or when excessively low impedance toground develops, which might expose the patient to an unsafe
condition should an additional fault occur. When the total
hazard current reaches a 5-mA threshold, the monitor shouldalarm. LIMs must alarm when the fault current (from conductorto ground) is 5.0 mA or greater. LIMs must notalarm if current
is 3.7 mA or less. Be aware that the LIM does notbreak the
circuit like a GFCI. Excessive ground currents trigger alarms but
will not stop the power to the system.
LIMs must be tested after installation and every 6 months by
grounding hot and neutral through a resistor. Also, there must be
a check of the visual and audible alarms. The LIM must be tested28 Introduction to Biomedical Instrumentation

each month with the test button. LIMs with automated self-test
capabilities must be tested every 12 months .
Medical air: Air that is 19.5 –23.5% oxygen. It also has speci fi-
cations that limit contaminants such as moisture or bacteria.
Patient care location: Any portion of a facility where patients are
intended to be examined or treated. This environment is de fined
around the patient bed. The vicinity is defined as 6 feet around
the bed and 7 feet 6 inches above the floor below the patient. See
Figure 2.1.Patient connection: An intended connection between a device
and a patient that can carry current. This can be a conductive
surface (for example, an ECG electrode), an invasive connection
Figure 2.1. Patient care area.Patient safety 29

(for example, an implanted wire), or an incidental long-term
connection (for example, conductive tubing). This is notintended
to include casual contacts such as push buttons, bed surfaces,
lamps, and hand-held appliances.
Wet location: A patient care area that is normally subject to wet
conditions while patients are present (not routine housekeep-
ing). An example would include physical therapy areas wherewhirlpool baths are used.
Electrical wiring in the hospital
Interestingly, outlets in a hospital are usually wired with the groundpin at the “top ”of the outlet (see Figure 2.2). This is an NFPA 99
requirement. In states where NFPA is law (it is law in only about halfof the United States), outlets are wired in this orientation. However,older facilities and hospitals in states where NFPA is not law may
have outlets wired with the ground pin below the hot and neutral
pins. Outlets need to be hospital grade. These outlets, which have agreen dot stamped on the face, undergo rigorous testing. Prior to1996, electrical outlets in hospitals had to be checked (integrity,polarity, and ground connection) once per year. In 1996, theregulations regarding the frequency of testing of receptacles was
changed. No time interval is now speci fiedexcept for non –hospital-
grade receptacles, which must be tested at least once every 12
months. Therefore, most hospitals use hospital-grade receptacles(in patient care areas) so that they do not need to be checked.Electrical outlets also have a speci fied amount of “holding power ”
for the ground pin. The code requires retention force of grounding
blade of not less than 4 ounces .30 Introduction to Biomedical Instrumentation

Some hospital outlets are colored red (either the receptacle
itself or its cover faceplate). This indicates that the outlet is wired
to emergency power (see emergency power time speci fications) in
the event of an outage. Typically, life-saving devices, such asventilators, are connected to the emergency red outlets.
Wire gauge for power cord ground conductor: If the length of
the power cord is less than 15 feet, use 18 AWG; if the length is
greater than 15 feet, use 16 AWG.
Figure 2.2. Hospital electrical outlet (dot indicates hospital grade).Patient safety 31

Standard colors for wiring: The black = hot, white = neutral, and
green = ground.
Placement in the clinical laboratory: Electrical outlets must be
installed every 1.6– 3.3 feet.
Ground impedance: Both capacitive reactance and resistance
between either the hot or the neutral conductors and ground
must exceed 200 kilo ohms (k Ω) in an isolated system. This must
be tested in 10% of outlets during new construction.
Emergency power: Power must be available within 10 seconds.
Electrical outlets connected to emergency power are colored red
(or their faceplates are labeled “emergency power ”).
Extension cords are allowed to be used within the hospital;
however, three-to-two-prong adapters are not allowed.
Two-wire (ungrounded) power cords: The NFPA code states
that all devices must have three-wire power cords with a three-
prong plug. However, devices that are double insulated can havea two-conductor cord and two-prong plug. A device that is
double insulated will be marked on the case using a square inside
a square symbol.
Extension cords in operating rooms: According to the code, the
power cord from a device must be “continuous and without switches
from appliance to the attachment plug ”(NFPA 99 7– 5.1.2.5). This
has been interpreted as forbidding extension cords in anesthetizing
locations (which is generally the same as operating rooms). The
only exception is a permanently mounted power cord on amovable equipment assembly like a rack or table (an outlet strip).32 Introduction to Biomedical Instrumentation

(Anextension cord is defined as a cord that has a male
connector on one end and a female connector on the other end
and that is intended to allow the power cord from a device to be
connected to a power outlet further in distance from the devicethan the length of the device power cord.)
Please note that there is no limit to the length of a power cord
for a device in operating rooms. Some hospitals replace shorterpower cords with longer ones to eliminate the “too far from the
outlet ”issue. This also diminishes the need for extension cords.
Outlet strips in operating rooms: The code states that it is
possible to use a hospital-grade outlet strip as long as it is per-manently mounted to a rack or table. In addition, the totalcurrent drawn by all of the appliances cannot exceed 75% of thecurrent capacity of the strip.
Ceiling-mounted receptacles and drop cords in operating
rooms: The receptacles are the twist-lock type.
Ground-to-chassis resistance measurement: The resistance
between the device chassis, or any exposed conductive surface ofthe device, and the ground pin of the attachment plug shall be
measured. The resistance shall be less than 0.50 ohm ( Ω).
Manuals
NFPA speci fically requires that the vendor supply suitable
manuals for operators and users upon delivery of the appliance.
“Purchase speci fications shall require the vendor to supply suit-
able manuals for operators and users upon delivery of thePatient safety 33

appliance. The manuals shall include installation and operating
instructions, inspection and testing procedures and maintenancedetails” (7–6.2.1.8). This is often cited in a purchase agreement as
a method for the hospital to obtain maintenance materials andcircuit diagrams from the manufacturer.
The manuals must include:
▶Illustrations that show location of the controls
▶Explanation of the function of each control
▶Illustrations of proper connection to the patient and otherequipment
▶Step-by-step procedures for proper use of the appliance
▶Safety considerations in application and in servicing
▶Difficulties that might be encountered, and care to be taken
if the appliance is used on a patient simultaneously withother electrical appliances
▶Schematics, wiring diagrams, mechanical layouts, parts lists,
and other pertinent data for the appliance as shipped
▶Functional description of the circuit
▶Electrical supply requirements, weight, dimensions, and
so on
▶Limits of supply variations
▶Technical performance specs
▶Instructions for unpacking
▶Comprehensive preventative and corrective maintenance andrepair procedures
The NFPA Life Safety Code 101
The NPFA Line Safety Code 101 is meant to provide minimumregulations to protect occupants of many types of buildings34 Introduction to Biomedical Instrumentation

including day care facilities, high-rise structures, stores, factories,
and hospitals. The code covers:
▶Means of egress
▶Occupant noti fication (fire alarms and drills)
▶Interior finish, contents, and furnishings
▶Fire protection equipment
▶Building services
The code contains a great deal of information necessary for safedesign and construction of the facility. The code is different fornew and existing heath care facilities. This information can besummarized as follows:
▶Compartmentation of fire is required because evacuation
cannot be ensured.
▶Automated sprinklers are required for new construction andmajor renovations.
▶The number of floors permitted is related to the type of
construction (for example, the exterior of a building withfour or more floors must be made from a noncombustible
material or limited combustible material).
▶Planning for the relocation of patients in a fire must include
movement of patients in their beds.
▶Doors to patient rooms are not permitted to lock, exceptwhere the needs of the patients require locked doors andkeys are carried by the staff at all times.
▶Doors in most corridors and walkways may only be held
open by automatic release devices that close in case of fire; in
order to avoid staff using objects to hold doors open, doors
should be equipped with automatic hold open devices.
▶Two exits must be provided from each floor.Patient safety 35

▶Most service rooms (housekeeping, facilities) must have a
one-hour fire rating.
▶Every patient room must have a window.
Government regulations
TheMedical Device Amendment, May 28, 1976, gave the Food
and Drug Administration (FDA) authority to regulate medical
devices. The Safe Medical Device Act of 1990 and Amendments
of 1992 require hospitals to identify and report serious problems
with medical devices.
Hospitals must file an MDR (which stands for medical device
reporting) when it is determined that a device has caused or con-
tributed to a patient death or serious injury. These reports must be
submitted within 10 days from the time personnel become aware
that the device has caused or contributed to injury or death. Anonline database of these reports is available and can be searched.
What does health insurance reform have to do with medical
devices? The Health Insurance Portability and Accountability
Act of 1996 (HIPAA) has requirements regarding privacy of
medical information. Since patient information is often storedin the memory of medical devices, some BMETs work to ensurehospital compliance with the privacy of the information. Theymake sure there are limitations regarding who has access to the
stored data as they carefully work to protect patient privacy.
STUDY QUESTIONS
1..Describe a scenario that would result in macroshock. Identify
the power source.36 Introduction to Biomedical Instrumentation

2..Describe a scenario that could result in microshock. Identify
the power source and describe how the current travels throughthe patient.
3..Describe the conditions under which electrical current can beused to correct the electrical signals of the heart.
4..Make a list of some of the guidelines related to equipmentpower cords.
5..Make a list of some of the guidelines related to power outlets.
6..Make a chart that shows the currents necessary to trigger the
action of a LIM and a GFCI. Include a column that shows
whether the circuit is open or closed above the trigger currents.
7..Summarize NFPA 101 requirements.
8..Describe the role of the federal government in medicalequipment regulations.
9..Summarize how HIPPA impacts what BMETs do.
FOR FURTHER EXPLORATION
1..Leviton is a manufacturer of hospital-grade outlets and plugs.Use its brochure Industrial Wiring Devices for the Health Care Industry
(available on the Internet; use quotes around the title in a searchengine to locate the correct page) to summarize the testingrequired in order to be labeled “hospital grade. ”Describe why this
is useful for outlets designed for the hospital environment.
2..There has been some discussion about UL regulations forrelocatable power taps (outlet strips) and the rules that apply to
hospitals. The confusion has prompted a new speci fic exclusion
for hospitals. Summarize this ruling, which can be found at
http://ulstandardsinfonet.ul.com/scopes/1363.html (scroll downto the end of the page).Patient safety 37

3..What is the major difference between a LIM and a GFCI? Why are
LIMs (instead of GFCIs) speci fically used in the operating room?
4..Why do you think the regulation for power strips limits the
items connected to the strip to 75% of the strip ’s rated value?
Describe how this could be implemented/restricted in the
clinical setting.
5..Twist lock power cords are required for power cords that dropfrom the ceiling. This is fairly common in the operating room tolimit power cords on the floor. Use the Internet to research the
look of twist lock connectors. Describe the bene fits they offer to
the situation over common prong electrical connections.
6..A common set of questions on certi fication exams includes the
numerical data points set by NFPA. Prepare a list of suchrequirements including:
▷Leakage current for portable equipment
▷When a GFCI must trip
▷Retention force of grounding blade
▷When an LIM must alarm
▷Wire gauge requirement for power cord ground conductor
▷Availability of emergency power
▷Ground-to-chassis resistance measurement
7..Use the Internet to research the history of the FDA and itsinvolvement in medical device design, manufacture, and use.Summarize the history including historical milestones. Provideyour opinion as to whether the FDA has been able to “keep up ”
with regulations in light of changing technology.
8..Explore the database of device problems on the FDA site: The
address for a search is http://www.accessdata.fda.gov/scripts/
cdrh/cfdocs/cfmdr/search.CFM. To enter a search string, usea device name from this text. Search for an incident andsummarize it. Discuss the role of human error and device flaws
(in design or function) in this incident.38 Introduction to Biomedical Instrumentation

3
In the workplace
LEARNING OBJECTIVES
1.list, describe, and characterize applicable codes of ethics,
with patient safety and confi dentiality as primary concerns
2.list and describe commonly used test equipment
3.list and describe safety universal precautions and personal safetymeasures
4.list and describe the qualities of excellent customer service
39

Introduction
As part of the health care team, BMETs must strive to serve the
staff and patients in the safest and most effective ways possible.
This chapter reviews the various ethical codes that may apply toBMETs. In the health care workplace, test equipment is used toensure patient safety. Precautions are employed to promotepersonal safety. In addition, serving staff and patients requiresexcellent customer service skills. These important facets of the
BMET workplace are explored.
Applicable codes of ethics
No code of ethics speci fically and exactly addresses the needs of
hospital-based BMETs. Two codes, however, have parts that
apply to BMETs. First, there is the Code of Ethics from theBiomedical Engineering Society (http://www.bmes.org). Even
though this group is research oriented, it does have a section that
applies to BMETs in the hospital environment.
Biomedical Engineering Professional Obligations
Biomedical engineers in the fulfillment of their professionalengineering duties shall:1..Use their knowledge, skills, and abilities to enhance the
safety, health, and welfare of the public.
2..Strive by action, example, and in fluence to increase the
competence, prestige, and honor of the biomedical
engineering profession.40 Introduction to Biomedical Instrumentation

Biomedical Engineering Health Care Obligations
Biomedical engineers involved in health care activities shall:1..Regard responsibility toward and rights of patients,
including those of con fidentiality and privacy, as their
primary concern.
2..Consider the larger consequences of their work in regard to
cost, availability, and delivery of health care.
A second group has developed an applicable code of ethics.
The American College of Clinical Engineering (ACCE) has
established the following guidelines:
PreambleThe following principles are established to aid individuals prac-
ticing engineering in health care to determine the propriety of their
actions in relation to pat ients, health care personnel, students, cli-
ents, and employers. In their professional practices they mustincorporate, maintain and promote the highest levels of ethicalconduct.
Guidelines principles of ethics
In the fulfillment of their duties, Clinical Engineers willHold paramount the safety, health, and welfare of the public
Improve the efficacy and safety of health care through theapplication of technology
Support the effi cacy and safety of health care through the
acquisition and exchange of information and experiencewith other engineers and managers
Manage health care technology programs effectively andresources responsiblyIn the workplace 41

Accurately represent their level of responsibility, authority,
experience, knowledge and education and perform servicesonly in their area of competence
Maintain con fidentiality of patient information as well as
proprietary employer or client information, unless doing sowould endanger public safety or violate any legal obligations
Not engage in any activities that are con flicts of interest or
that provide the appearance of con flicts of interest and that
can adversely affect their performance or impair their
professional judgment
Conduct themselves honorably and legally in all their activities
This can be found on the Web site at http://www.accenet.org/;
at the “Publications and Practices ”tab, select “Professional
Practices. ”
To summarize these codes, the essential foundation and
guiding principle puts patient safety as primary in all activities.In addition, patient privacy is paramount. The Health Insurance
Portability and Accountability Act of 1996 compels BMETs to
ensure patient privacy.
Test equipment for the BMET
Many different types of tests must be performed on medicalequipment. To accomplish this, there are devices speci fically
designed to check the performance or safety of this equipment.Some test equipment can simulate patient physiological signals
and are used to verify proper performance of devices.
Some companies produce equipment for most testing needs
of BMETs. Major manufacturers include BCGroup, Dale Tech-
nology, Metron, and Fluke Biomedical. Some manufacturers42 Introduction to Biomedical Instrumentation

provide very speci fic testing devices made to interface with spe-
cific pieces of equipment.
Guidelines of best practice and some regulations may require
testing of equipment for chassis leakage and ground resistance.
Also, outlets must be checked for polarity under certain condi-tions. Devices that will automatically check and then measurethese variables in the specified conditions are often called safety
analyzers (see Figure 3.1).
Some specialized test equipment is designed to perform vari-
ous kinds of recommended tests. For example, patient leads forcardiac monitors must be tested for electrical isolation. Numeroustest devices that will perform this test are available. BMETs can alsouse a specialized device to test GFCIs. De fibrillators and electro-
surgical units must also be tested for proper output. There arespecific devices designed to test these pieces of equipment. Some of
the types of test equipment are made by the manufacturer just for aparticular machine; others are more generic. Devices like IV pumps,ventilators, pulse-ox devices, and ultrasound machines all requireperformance testing, and many have unique devices to check them.Figure 3.2 shows a BMET testing the output of a de fibrillator that
is part of a “crash cart. ”During cardiac emergencies, crash carts
contain items that can be used to resuscitate a patient. Properperformance of de fibrillators in emergencies is essential and so
they are regularly tested.
BMET personal safety
Universal precautions and isolationYou must assume every patient and every piece of equipmenthas a communicable disease that could be transmitted to you.In the workplace 43

Using universal precautions treats all human blood and certain
human body fluids as if they are infectious for HIV and other
pathogens. In general, AIDS is the only infectious disease for
which a patient cannot be tested without patient permission.
Figure 3.1. Safety analyzer and patient simulator. (Photo courtesy of BC Group.)44 Introduction to Biomedical Instrumentation

Figure 3.2. A BMET testing a de fibrillator.In the workplace 45

Consequently, hospitals assume all patients and all fluids
associated with the patient are contaminated. Almost all bodily
fluids and some body parts are systematically treated with the
utmost care. The bodily fluids on the precautions list include
semen, vaginal secretions, cerebrospinal fluid, synovial fluid,
pleural fluid, pericardial fluid, peritoneal fluid, amniotic fluid,
saliva in dental procedures, any body fluid that is visibly con-
taminated with blood, and all body fluids in situations where it
is dif ficult or impossible to differentiate between body fluids.
Interestingly, sweat is not included in this list. The body parts
on the precautions list include the mucous membranes and anybody tissue or organ (other than intact skin) from a human(living or dead).
Precaution standards
The Centers for Disease Control and Prevention (CDC) hasidenti fied two basic classes of standards: standard precautions
and transmission-based precautions.
Standard precautions are to be considered and used for every
patient and every piece of patient equipment encountered.
Standard precautions combine Universal precautions (blood and
body fluid precautions) and the use of personal protective
equipment ( PPE) to provide a barrier between moist body
substances (for example, blood, sputum, and secretions) and
health care workers and visitors. PPE may include gloves, glasses,gowns, face shields (see Figure 3.3), and masks. Use of standardprecautions takes into consideration that sources of infection may
be recognized or unrecognized as infectious at the time of
exposure.46 Introduction to Biomedical Instrumentation

Transmission-based precautions are designed for patients
documented or suspected to be infected or colonized with highly
transmissible pathogens for which additional precautions areneeded to interrupt transmission. These precautions are used in
Figure 3.3. Personal protective equipment –mask with eye shield.In the workplace 47

addition to standard precautions. Transmission-based precau-
tions include airborne, droplet, and contact isolation. You needto learn the facility-speci fic signage associated with each of these
isolation types so that you are aware of the practices requiredbefore entering a patient care environment.
▶Airborne precautions –Follow these precautions around
patients known or suspected to have serious illnessestransmitted by airborne droplet nuclei. Examples of suchillnesses include measles, varicella (chicken pox), andtuberculosis.
▶Droplet precautions –In addition to standard precautions,
use droplet precautions for patients known or suspected tohave serious illnesses transmitted by large particle droplets.Examples of such illnesses include invasive Haemophilus
influenzae type b disease, including meningitis, pneumonia,
epiglottitis, and sepsis, and invasive Neisseria meningitidis
disease.
▶Contact precautions –In addition to standard precautions,
use contact precautions for patients known or suspected tohave serious illnesses easily transmitted by direct patientcontact or by contact with items in the patient’ s environ-
ment. Examples of such illnesses include gastrointestinal,
respiratory, skin, or wound infections or colonization with
multidrug-resistance.
Customer service
When a BMET has a positive experience with a clinical staffmember, especially in a time of diffi culty, it can greatly improve48 Introduction to Biomedical Instrumentation

future interactions and positively impact patient care. Under-
standing how to approach stressful situations and communicateeffectively is a learned skill that can be perfected over time. How-
ever, some important skills, speci fict oB M E T s ,c a nb ei d e n t i fied.
▶Exercise generally accepted best practices of effective customerservice. These include compassion, friendliness, advocacy,
commitment to excellence, flexibility, and willingness to help.
▶Be responsive, respond to phone calls, pages, and emailmessages. Respond as quickly as possible, even if it is only toarrange follow-up at a later time.
▶Initiate ongoing communication. Visiting units at times
when there is not a problem can build rapport and trust
between the BMETs and staff.
▶Listen to a staff member ’s interpretation of a problem,
even when it ’s improbable; it can build communication for
future scenarios –when the staff member might be correct.
▶Understand that the stress on the medical staff due toa technological malfunction may be enormous because theirability to treat the patient is compromised. What may seemminor to a BMET may be huge to the medical staff.
▶Be sensitive about communicating to the device user thesource of a problem after a speci fic solution is identi fied,
especially if the staff may have overlooked a simple solutionin the stress of the moment. It may be a good idea to waituntil stressful emotions have passed to communicate theoverlooked step. Using the opportunity to explain how simplesituations escalate can avoid repetition of the problem.
▶Identify processes that can avoid the simplistic commun-
ication of “broken. ”One word descriptors are not very useful
in BMET problem solving.In the workplace 49

▶Be constantly aware of opportunities to clarify equipment
function to avoid problems. If a problem seems to occurfrequently, staff instruction or procedural changes can
decrease the dif ficulties.
▶Do your homework! Keep up with the treatment trends and
technologies. Make use of all available resources includingthe Internet to be knowledgeable and helpful. Technology isalways evolving, and BMETs need to know where to obtaininformation when presented with a device or situation with
which they are unfamiliar.
One of the most valuable skills you can acquire is an
ability to look at the human body without giggles or disgust.
Better said, BMETs need to have a professional attitude and
calm composure when working around patients. Prior to ahospital career, most people have little exposure to the nakedadult human body. The clinical environment requires an
entirely new perspective. Effective and professional BMETs are
calm and focused to the best of their abilities, often instressful situations. The human body is not “pretty ”in
trauma and disease. The composure of a BMET, as a valuedmember of the health care team, is the most important itemin the BMET tool kit.
STUDY QUESTIONS
1..Summarize the primary ethical qualities for BMETs that are
reflected in the various codes of ethics.
2..Identify and describe some of the equipment tests that are
performed by BMETs.50 Introduction to Biomedical Instrumentation

3..Describe a scenario in which a BMET would use PPE and be
aware of the potential of patient fluid contamination.
4..Define and describe standard precautions.
5..Describe the bene fits of effective customer service interactions
with medical staff.
6..Identify some of the methods BMETs use to keep up to datewith equipment and treatment innovations.
7..List and describe the qualities of a BMET that illustrate theprofessional attitude recommended in the chapter.
FOR FURTHER EXPLORATION
1..What happens to a BMET if he or she does not act ethically? Isthere a consequence for violation of the HIPPA right to patient
privacy? Since there is no BMET “license ”that can be removed
for unethical behavior, what other means are there to ensure
that BMETs act responsibly? Use the Internet to research yourresponse and document your answer.
2..Discuss the advantages and disadvantages of a licenserequirement for BMETs to practice in the clinical setting.
Identify medical staff who are required to obtain a license
(excluding doctors and nurses). Are there other medical staffwho do not work directly with patients who need a license? Use the
Internet to research your response and document your answers.
3..Browse through the Web sites of the test equipmentcompanies to view some of the specialty testing devices.
Summarize the types/categories of equipment available. How
would a BMET department select devices to purchase?Discuss the importance of high-quality functioning testequipment in device support.In the workplace 51

4..Some manufacturers restrict the purchase of specialized test
equipment until service training has been completed by aBMET from the hospital. Why would this be a requirement?
What are the advantages and disadvantages of this restriction?
Discuss the economic impact of this type of restriction.
5..If one BMET from a department is sent for specialized trainingon a device, discuss the dif ficulties that person might
experience in supporting all the devices all the time. Describesome of the ways a department could share the knowledge to
share the equipment support.
6..Patient isolation is one method of transmission restriction.
Explore the CDC Web site for the standards for patient
isolation: http://www.cdc.gov/ncidod/dhqp/gl_isolation.html.Summarize the information found there. Carefully identifythe ways a BMET would know a patient was subject to
isolation.
7..Explore general customer service skills information available on
t h eI n t e r n e t .S u m m a r i z es o m eo ft h eb a s i cp o i n t s .H o wd o e sthe general information, say for retail sales, apply to theclinical setting? In what ways are customer service skills moreimportant in a clinical setting than a retail establishment?
Identify how a BMET can obtain customer service training.52 Introduction to Biomedical Instrumentation

4
Electrodes, sensors, signals, and noise
LEARNING OBJECTIVES
1.list and describe what a sensor does
2.identify the two types of transducers and describe examples of
each type
3.list and describe the sources of error in sensor systems
4.list and describe the four types of electrodes (surface, micro,
indwelling, and needle)
5.list and describe the sensors that are used to record direct bloodpressure and temperature
6.list and describe impedance matching and patient impedance
7.list and describe human periodic, static, and random signals
8.characterize human signals as analog and medical devices asdigital
9.describe electrical noise, especially related to the clinical setting
53

Introduction
The most common activity in patient care is patient monitoring.
The human body produces a variety of physiological signals, and
physicians have learned to interpret these signals to provideinformation about the health of a patient. To measure ormonitor these signals, there must be a connection between thepatient and some (typically electronic) device. This type of activityis called in vivo monitoring, which refers to the living patient.
This chapter explores the machine-human connection.
Sensors
Sensors (often called transducers –the difference is unimportant
here) convert the energy of the patient (pressure, for example)into a form that can be used by an instrument. There are two types
of sensors/transducers:
▶Some transducers ’output changes in response to a
change in surroundings. The output is a change in
resistance, capacitance, or inductance . These variations
can then be measured, often using Wheatstone bridge
circuitry because the changes may be very small. Commonexamples include:
▷Strain gauges –Change in resistance when some external
event occurs.
▷Potentiometers (variable resistors) –Change in resistance
when some external event occurs. Since these devicesoften have a mechanical knob or lever, they often convertmechanical movement or position into a change inresistance.54 Introduction to Biomedical Instrumentation

▷Thermistors –Change in resistance when temperature
changes.
▷Photoresistors –Change in resistance when light hits
the device.
▶Some transducers produce a voltage or current in response
to a change in environment. Common examples include:
▷Piezoelectric crystals –Produce a voltage as the crystal
is compressed (even tiny amounts).
▷LVDTs (linear variable differential transformers) –
Convert linear motion (may be very small amounts)
into an electrical signal.
▷Thermocouples –Measure temperature differences
using dissimilar metals. They require a knownreference temperature.
Note: There are many types of sensors/transducers. Commonly
seen ones are described here, but engineers create specialized and
unique devices to serve particular needs.
When blood pressure is measured directly (in an artery), it is
commonly measured using strain gauges, piezoelectric crystals,
and silicon membranes. The hospital environment is very phys-ically demanding on equipment. Even though transducers areusually used only once (disposable), a good transducer must be
very durable.
Optical devices
Photoemissive devices
Photoemissive devices are common and useful because of the
relationship between electrical behavior and light. They are able
to create light under certain conditions.Electrodes, sensors, signals, and noise 55

Alight-emitting diode (LED) is a semiconductor device that emits
light when it is biased in the forward direction. The color of the
emitted light depends on the chemical composition of the material
used in the semiconductor. It can be visible light (see the list of
colors in the next paragraph), infrared, or nearly ultraviolet. LEDsare used as indicators in many devices. A green indicator mayindicate that power is applied, while a red LED could indicate anonfunctioning circuit. Applications are manufacturer-speci fic.
LEDs emit the following different visible colors:
▶Red
▶Orange
▶Yellow and “amber ”
▶Green
▶Blue-Green
▶Blue
▶White
PhotodetectorsThese devices can respond to light by transforming light energy
under certain conditions. There are two types of photodetectors:
photocells and photodiodes.
▶Photocells convert light into energy (usually a voltage
or current). A light-sensitive cathode emits electronswhen light hits it. The emitted electrons are then collectedat the anode, which results in electrical current. Photocellsare also used as detectors in spectrophotometry.
▶Photodiodes, also called light-detecting diodes (LDD), are
made of silicon that generates an electrical signal (usually a56 Introduction to Biomedical Instrumentation

voltage) when light hits the diode. Photodiodes are also used
as detectors in spectrophotometry, pulse oximetry, opticalglucose meters, and laboratory equipment that measures
blood plasma elements.
Important sources of error in systems with sensors
There are many opportunities for systems to incur error. Here are
some general and common types of error and opportunities forunreliability:
Insertion error: The sensors interfere with the system and
affect either the measurement or the system. This is often the
case when the item that links the equipment to the patientcauses some distortion or change in the signal to be measured.
(For example, when patients und ergo sleep analysis, they must
sleep with a large amount of sensors attached to them. This
may make the sleep an inaccurate representation of the typicalsleep patterns.)
Environmental error: The hospital is a very abusive place: It is
“rough ”on sensors (they are dropped, for example). Patients and
devices are often moved from place to place. Also, many staff
members use the equipment on many different patients. For
example, perhaps the environmental temperature in one situ-ation is very different from that in another situation.
Hysteresis: It is dif ficult to have a sensor behave exactly the same
way when “loaded” as it does when “unloaded. ”For example, if
you measure three temperatures –one low, one high, and thenElectrodes, sensors, signals, and noise 57

one low –will the sensor be able to return to the low temperature
accurately the second time, or will the exposure to the high
temperature limit the device ’s ability to take a low reading?
Electrodes
Many important human physiological signals are electrical. Anelectrical connection is necessary to connect the patient to the
device. Electrodes are often used to pick up the signals.
Of all the connections made, surface electrodes are the
most common. Surface electrodes make the connection to the
patient, in vivo, which means on living people. These are used
in electrocardiograms (heart; ECGs or EKGs), electromyograms(muscle; EMGs), and electroencephalogram (brain; EEGs). These
electrodes often use a metal conductor surrounded by a con-
ductive, jelly-like material (usually embedded in a sponge-likematerial) and some sticky plastic foam to hold these compon-ents in place. See Figure 4.1. These electrodes do not piercethe skin.
Figure 4.1. Surface electrodes (the electrolyte-soaked sponge has been removed from the
electrode on the left).58 Introduction to Biomedical Instrumentation

The major dif ficulties with surface electrodes are:
▶ “Stick ”problems –how to attach them to the patient
▶Motion of the patient
▶High impedance of human skin, especially if it is dry or hairy
▶Patient environment –some patients may be in a wet
environment, for example, which can hinder the electrode
connection
▶Available skin surface area –neonates and burn patients can
present challenges because they have limited available skinfor connection
These diffi culties can diminish the signal strength or distort the
signal in a way that makes it dif ficult to use for the diagnosis of
patient conditions. As a result, efforts are made to diminish theimpact of these situations. For example, hairy skin may be shavedto promote good electrode contact. Many devices have built-inalgorithms that reduce the impact of motion on the signal.Research into the creation of “better ”surface electrodes is ongoing.
Table 4.1 lists some types of electrodes. A good example of
the use of a needle electrode is in fetal monitoring (see Figure 4.2).
An electrode is attached to the head of a fetus before delivery.Scalp electrodes penetrate the skin of a baby prior to delivery. The
long wire has a metal spiral tip that is twisted into the scalp inorder to obtain ECG readings. For high-risk deliveries, this is animportant monitoring technique.
Measuring temperature
Temperature is a very common variable to be measured. Patienttemperature is very important in the assessment of patientElectrodes, sensors, signals, and noise 59

condition. Typical patient temperature ranges are shown in
Table 4.2. The core human body temperature can be in fluenced by
many things including pregnancy, smoking, the environment, and
other conditions that in fluence the body ’s ability to control its own
temperature. Thermistors are often used to measure skin or internal
patient temperature. They are inexpensive, relatively rugged, and
nonlinear. Circuitry that processes the sensor ’s data can compen-
sate for the nonlinearity. Thermocouples that require a reference
temperature are also used, as are solid-state temperature sensors.TABLE 4.1. Other types of electrodes
Types of electrodesWhat signal is the
electrode used tomeasure?How is the electrodeattached to the patient?
Needle electrode EEG and ECG Slightly below the skin
Indwelling electrodes Specialized heart signals Often threaded
through the patient ’s
veins
Microelectrode Cell potentials Not often attached to
patients, often used in
research
Figure 4.2. Microelectrodes that twist into the scalps of neonates during delivery.60 Introduction to Biomedical Instrumentation

Impedance matching
To pass a signal from the patient to the device, the patient and
the device input must have the same (or close) impedance. Since
thepatient is usually a high-impedance source, ampli fiers are needed
to match the high impedance. Devices are designed with thisimpedance matching in mind.
Human signals
The human body produces a wide variety of electrical (and other
types of) signals, which are a perfect source of information for the
medical community. Signals can be grouped into three types:periodic, static, and random.
Periodic signals (sometimes called repetitive signals) are
symmetric and repetitive signals. An ECG, for example, has avery predicable pattern (unlike an EEG, which has a variablesignal). Other examples of perio dic signals are blood pressure
waveforms and respiratory waveforms. Periodic waveforms are
commonly monitored, and their frequency is counted (and
recorded or displayed). Periodic waveforms are shown in Figure 4.3.
Static signals are very regular and unchanging. Temperature is
a good example; it might change, but it does so very slowly andTABLE 4.2. Typical patient temperatures
HypothermiaNormal body
temperature (core) Fever/hyperthermia
86–95°F 97.5 –98.9°F 99 –107°FElectrodes, sensors, signals, and noise 61

in very small increments. These signals often appear on a
display as a straight line.
Random signals seemingly have no pattern, although some
signals (like an EEG) may have some common characteristics.Random signals may have a common frequency but still have an
Figure 4.3. Periodic signals.62 Introduction to Biomedical Instrumentation

unpredictable waveform. Electromyograms, which record the
electrical activity of muscles, also fitt h i st y p eo fs i g n a l .R a n d o m
waveforms are shown in Figure 4.4.
Signal conversion
Most (if not all) physiological signals are analog; most (if not all)monitors and medical devices are digital. Because of the differingsignals, conversions are necessary to coordinate communication
between the patient, the sensors, and the signal processing
systems.
Analog-to-digital conversion: A varying, analog signal from the
patient is converted into ones and zeros in a process that is often
called A/D conversion. There are many ways to perform this
conversion. An illustration of this process is shown in Figure 4.5.
Digital-to-analog conversion: A digital signal of ones and zeros
is converted into an analog signal in a process that is often called
Figure 4.4. Random signals.Electrodes, sensors, signals, and noise 63

D/A conversion. This may occur when a display of a waveform is
created. Again, there are many methods to perform this.
Signal noise
Signal noise, or interference with the monitoring of human
electrical signals, can hinder accurate patient observations. Whatare the sources of signal noise?
▶Lights (especially the 60-hertz (Hz) “hum ”from flourescent
fixtures) –All electricity is received from the power company
at a frequency of 60 Hz.
▶Human body –The many signals within the body operate at
different voltages and frequencies. These systems include thebrain, the heart, the muscles, and the digestive system.
▶Computers and their cables –These can add signal noise
and electromagnetic interference.
▶Other machines being used –Those machines that generate
electrical energy or have motors (such as electrosurgical unitsin the operating room) are a common source of interference.
Figure 4.5. Analog-to-digital conversion.64 Introduction to Biomedical Instrumentation

Signal conditioning
The instrumentation amplifi eris the backbone for most
medical instrumentation. It matches impedance and provides
amplifi cation and signal conditioning for physiological signals
from the patient.
Theisolation ampli fieris basically a safety device. Because the
patient needs to be protected from the monitoring circuitry andyet the physiological signal needs to be evaluated, the isolation
ampli fier was developed. Many techniques are available to elec-
trically isolate the equipment from the patient; however, most
systems use an optical link.
A note about circuitry: The fundamentals of circuit layout and
troubleshooting were essential years ago. Good BMETs wouldevaluate component performance and replace individual items
when necessary. As technology has evolved, there has been a shift
in emphasis from components to circuit boards. In general, thisshift has diminished the time spent analyzing common circuitsor the ability to replace malfunctioning components such ascapacitors or transistors.
STUDY QUESTIONS
1..Definein vivo monitoring in humans. Provide an example.
2..What is the fundamental purpo se of sensors when used in
patient care?
3..Briefly characterize known source s of error in sensor systems.
4..Describe the components of a surface electrode and the
purpose of each part.
5..Describe some of the challenges of the connection between thesurface electrode and human body.Electrodes, sensors, signals, and noise 65

6..Compare and contrast surface electrodes and needle electrodes.
7..Compare and contrast periodic signals and random signals and
give examples of each.
8..Identify and describe some sources of noise in humanmonitoring.
FOR FURTHER EXPLORATION
1..The clinical setting can be a tough place for sensors. Patients arenot always docile; devices must be thoroughly cleaned; anddropping, banging, and smashing devices are a secondary resultof the fast-paced environment of patient care. How does thisinfluence the design of sensors? How can BMETs balance the
needs of staff to care for patients and the need to preserve
technology? Examine the sensors described in this chapter and
evaluate their durability and appropriateness for the clinicalsetting.
2..What are some of the signi ficant advantages of using LEDs as
indicators in medical devices? Discuss their durability, life span,and electrical requirements.
3..A number of devices employ human physiological signals butmay not be commonly used in patient care. For example, manylaptops have the capability to use biometrics to identify theuser. Some gaming consoles use sensors to detect playermotion. Explore some of these sensors used to interfacehumans to devices (not necessarily medical applications).
Describe these sensors. Use the Internet to research and
document your answers.
4..Researchers who investigate the human body using animalexperimentation often employ unique sensors to measure a66 Introduction to Biomedical Instrumentation

wide variety of variables. Use the Internet to explore animal
sensors. Select several and describe how they are made andwhat they measure. How do they differ from those found in the
clinical setting?
5..Biofeedback is a common practice using human signals
converted to sound. Explore this process to understand howthe mind can be trained to control physiological signals.Identify the signals commonly used in this technique. Describethis process and its believed bene fits to people who use it.
6..Research some human physiological signals. Describe thesignals and how they may be measured. Identify whether thesignal is electrical, mechanical, or some other type.
7..Many of the devices described in this book use sensors toextract physiological data from patients. Research devicesdescribed in this book on manufacturers ’Web sites. Describe
which type of sensor is used and the type of data retrieved. Bespecific about the sensor, identifying the electronics or
mechanical system involved.
8..Use the Internet to explore an instrumentation amplifi er
circuit. Obtain a simple circuit diagram. Identify and describethe basic functions of the parts of the circuit. Follow the
physiological signal through the circuit.
9..The ability to regulate our core body temperature can be
compromised by many situations, conditions, and diseases. Listand describe three such conditions. Infant prematurity canlimit the ability to control body temperature. Research therelationship between prematurity and temperature regulation.
Describe techniques that are used to assist newborn patients
with temperature regulation.Electrodes, sensors, signals, and noise 67

5
The heart
LEARNING OBJECTIVES
1.list and describe the purpose of patient monitoring
2.list and describe the characteristics of the ECG electrical
waveform
3.describe cardiac events such as MI and PVC
4.list and describe the differences between the 3-lead and 12-lead
ECG
5.list and describe the many names for the technique of bloodoxygen saturation measurement
6.describe the reasons that pulse oximetry monitoring is commonly
used
7.describe how pulse oximetry works
69

Introduction
The beat of the heart, including the electrical signal transmitted
to create the beat, is one of the most familiar waveforms found in
health care. It deserves this status. The electrical activity of theheart is fairly simple to measure and tells a great deal about thehealth of the patient. In the very early 1900s, Willem Einthovenwon the Nobel Prize in medicine for his work identifying andrecording the parts of the electrocardiogram.
Patient monitoring
Monitoring a patient ’s heart is a very common procedure. A
patient ’svital signs are often tracked at regular time intervals or
continuously (these are usually blood pressure and pulse –both
related to heart function). Technology can be used to track thepatient ’s condition without someone standing next to the bedside.
In addition to tracking the condition of a patient continuously,monitoring can provide diagnostic information upon whichtreatment decisions are based. Vital signs such as blood pressureand respiration are discussed in their respective chapters.
Note about assumptions for vital signs: Most patients in most
hospitals are adults (they are simply sicker more often). There-
fore, when a vital sign is listed and unlabeled (as to the age/type of
patient) it is assumed to belong to an adult.
Electrical activity of the heart
The heart generates electrical signals to contract (pump blood).
Cells within the heart have the ability to depolarize and70 Introduction to Biomedical Instrumentation

repolarize, and this process generates electrical energy. The
electrical signal in the heart begins at the sinoatrial (SA) node,which stimulates the atria (the two upper chambers of
the heart) to contract. The signal then travels to the atrioven-tricular (AV) node, followed by the Bundle of His, and thenthrough the Purkinje network, which stimulates the ventricles
(the two lower chambers of the heart) to contract. Whenthe ventricles are being stimulated to contract, the atria arerepolarizing.
The electrical signal is called an electrocardiogram . The
abbreviation used for this can be EKG (which comes from Ger-
man Elektrokardiogramm )o rECG (you will find these acronyms
used interchangeably). Some people prefer EKG since it isunlikely to be confused with the EEG when spoken. There is noconsensus on the label EKG or ECG. There may be times when
the terms are used together. As an example, an ECG monitor can
display a 12-lead EKG. Called either EKG or ECG, the electricalwaveform has a patterned shape, and its peaks are labeled withletters, as shown in Figure 5.1. Try to visualize the electrocar-diogram pattern as a re flection of the motion (contracting and
relaxing) of the heart.
The first little upward notch of the ECG waveform is
called the Pw a v e . The P wave indicates that the atria are
contracting to pump blood. The next part of the ECG is ashort downward section connected to a tall upward section.This part is called the QRS complex . When the Bundle of His
fires, the ventricles contract to pump blood. The large amplitude
of voltage is required because the ventricles are the most mus-cular and dense part of the heart. The next upward curve iscalled the Tw a v e . The T wave indicates the resting period
(repolarization) of the ventricles.The heart 71

The number of waves per minute is the heart rate . Notice
that heart rate is measured per minute rather than per second as
most other electrical signals.
The amplitude of the QRS segment can be measured at the
skin and is about 1 millivolt (mV).
ECG monitoring
ECGs can provide information about the condition of the patient.
Some physiological events that a medical team might look for
include:
▶Fibrillation –thefluttering of the heart, which is essentially
randomized electrical signals that result in chaotic andineffective contractions.
R wave
P waveT wave
Q wave S wave
Figure 5.1. ECG waveform.72 Introduction to Biomedical Instrumentation

▶Asystole –no electrical activity of the heart, “flat line. ”
Patients in this condition are clinically dead.
▶Rhythm disturbances –includes premature ventricular
contractions (PVCs), where the ventricles contract at the
wrong time.
▶Conduction abnormalities (disruption of the electricalpathways of the heart).
▶Size of the heart chambers (enlargement or atrophy).
▶Position of the heart in the chest (axis).
▶Rate at which the heart is contracting (bradycardia –too
slow, tachycardia –too fast).
▶Diagnosis of myocardial infarction (MI) (heart attack).
▶Ischemia (lack of blood flow to the heart) and other disease
states.
▶Effect of cardiovascular drugs.
▶In exercise testing, effects of physical workload upon the heart.
It is important to know what the ECG should look like because
it is often the job of the BMET to evaluate the performance of heartmonitors. However, the study of the subtle waveform changes thatoccur in disease conditions, although vital to the medical team, isnot required of BMETs. Therefore, a basic understanding of thegeneral ECG waveform characteristics is very important; however,
in-depth study of abnormalities is not required of BMETs.
Cardiac monitors typically display the ECG waveform as well
as a numerical display of the heart rate (beats per minute). In
addition, monitors have alarms that can be set to notify staff ifminimum and/or maximum heart rates are exceeded. This datamay also be networked to a central station. Typically located at
the front desk of a nursing unit, a monitor can display the ECG
waveforms of many patients.The heart 73

ECG waveforms are most often obtained from surface elec-
trodes stuck onto a patient ’s skin. It is important to note that
waveforms can also be obtained in other ways. One common
example is to monitor a fetus during delivery. An electrode wire is
connected to the skin of the head. The needle electrodes areexplained in Chapter 4.
Throughout electrical training, the terms “lead ”and “wire ”
are used interchangeably. This is not true for cardiologists andother clinicians. They define a lead as a view of the electrical
activity of the heart from a particular angle across the body.The wires connected to the patients are paired, in differentcombinations, to obtain the many views needed for clinicalinterpretation. Since voltage needs two connecting points, com-binations of the various connecting points (wires) provide clin-icians with leads or views .
Three-lead ECG monitoringOnly two connections are required to measure the electricalactivity of the heart. For example, a very basic ECG can readilybe seen by holding a lead in each hand and using some simplesignal processing ampli fiers. However, the importance of a
diagnostic-quality signal requires more attention to the patient
connections.
There are three connections to the patient in a three-lead
ECG . The connections are most often labeled RA (right arm), LA
(left arm), and LL (left leg). The labels may be a bit confusing
because the electrodes are often placed on the torso not the
extremities. The arm connections are usually placed near the
shoulders and the LL is placed near the bottom of the rib cage(patient ’s left side). Each lead graphically shows the voltage
(potential difference) between two of the electrodes. A three-lead74 Introduction to Biomedical Instrumentation

ECG illustrates the electrical activity of the heart in three different
ways using the three electrical wires connected to the patient:
Lead I –LA (positive) and RA (negative) (memory aid: one L
in the configuration)
Lead II –LL (positive) and RA (negative) (memory aid: two
Ls in the configuration)
Lead III –LL (positive) and LA (negative) (memory aid: three
Ls in the configuration)
One electrode is not used as a part of each of the lead selections. It
is used as the “ground ”reference lead. That is, if you are moni-
toring lead II (RA and LL), the LA electrode becomes the ground.
This combination comes from the work of Willem Eithoven and iscalled Eithoven ’s triangle. The leads, called bipolar limb leads,
form this triangle, which is illustrated in Figure 5.2.
Three-lead monitoring is the most common type of patient
connection to look at the electrical activity of the heart. Whenconstant monitoring is required, this method will be used.
Figure 5.2. Eithoven ’s triangle.The heart 75

However, a three-lead ECG does not give as much diagnostic
information as possible.
Five-lead ECG monitoring
Thefive-lead ECG provides six views of the heart. Three of the
views are the same as the three-lead ECG –leads I, II, and III –
plus three additional views called aV R,a V L, and aV F. These add-
itional leads are called augmented leads . More views provide the
medical team with more information with respect to heart tissue.
There are usually five patient connections, three connections in
the same locations as for the three-lead ECG. There are the same
two shoulder-area electrodes, LA and RA. The LL electrode is inthe same location, near the lower edge of the rib cage. Twoadditional electrodes are added to the patient: one below the ribcage on the right side (RL) and one close to the center of the
chest (Chest). RL is always the “ground ”reference lead.
12-lead ECG monitoring
A 12-lead ECG monitor uses ten electrodes , four attached to the
limbs (although often on the torso) and six connected in a lineon the chest wall. These connections to the patient are called
unipolar leads, can provide extensive information, and are
commonly used for diagnostic purposes. The electrode attachedto the right leg serves as a “ground. ”The electrodes can obtain 12
different voltages of the heart by making 12 comparisons.Accurate lead placement is extremely important. The views that
clinicians look at are I, II, III, aV
R,a V L,a V F,V1,V2,V3,V4,V5, and
V6. Note that the 12-lead ECG provides the six views from the
five-lead ECG plus six additional views. The addition of moreelectrodes attached to the patient’ s body expands the infor-
mation from two dimensions into three dimensions. The76 Introduction to Biomedical Instrumentation

diagnostic use of the additional leads is not within the scope of
this book; however, for cardiac patients, the additional infor-mation is very important.
Twelve-lead ECGs are usually done for diagnostic purposes,
and a patient typically is not connected to all ten electrodes allthe time. Twelve-lead tracings may be useful during stress testing(when the patient is constantly monitored during exercise oractivity). This provides the medical team with a great deal ofcardiac information.
Lead identi fication
To help clinicians properly place the electrical connections, color-
coding is used. In the United States,
RA connector has white snaps or wires
LA connector has black snaps or wires
LL connector has red snaps or wires
RL connector has green snaps or wires
Chest connector has brown snaps or wires
Clinicians use the following mnemonic device to remember
where to place the colored connectors: “Right is white ”to
remember to place the white lead on the (patient ’s) right-side
shoulder. “Black is opposite of white ”so black goes on the left
shoulder. Then “smoke over fire”reminds the clinician to place
the red lead under the black lead. “Green under white ”indicates
that the green lead is placed on the right leg, and the brown leadis often placed in the V
1position (near the center of the chest).
As a BMET, understanding where connections are made can
be very important when assessing a reported problem with anThe heart 77

ECG monitor. Often a problem lies with the connectors, elec-
trodes, and patient connections rather than the monitor.Evaluating electrode placement and condition can serve as a
starting place for the assessment of dif ficulties, problem reso-
lution, and communication with the clinical staff.
Long-term ECG recording
Long-term ECG recording, also called Holter monitoring, can
detect ECG abnormalities that may occur over time. The patient
wears ECG electrodes that are connected to a recording device
( o r i g i n a l l y ,H o l t e rm o n i t o r sw e r ec a s s e t t et a p er e c o r d e r s ,b u tnow they are digital recorders). The recording device is quitesmall and is shown in Figure 5.3. Patients wear these monitors
Figure 5.3. Long-term ECG recorder.78 Introduction to Biomedical Instrumentation

as they go about their normal activities. Typically these
recordings are done for 24 –48 hours.
Fetal heart monitoring
Heart monitoring of infants in the uterus is a common procedure.In a routine examination, a hand-held Doppler device is used. Thisuses ultrasound to detect fetal heart activity. Using ultrasound
allows the fetal heart rate to be detected even with the mother ’s
heart rate activity present. It also can be converted to sound to
“hear ”the heart beat. Observed heart rates are usually 120 –160
beats per minute. During labor, continuous monitoring is pre-ferred. The electrical activity of the fetus is monitored for signs ofstress and labor complications. Additional information and a
photo of a device used to monitor fetal heart rates during labor are
in Chapter 15.
During vaginal delivery, the heart rate of infants can be
electronically measured directly by placing a wire into thescalp. This is internal fetal monitoring . Needle electrodes were dis-
cussed in Chapter 4.
Pulse oximetry
Also called SaO 2, SpO 2, pulse ox, and sat or sats (short for sat-
uration), pulse oximetry is a simple, noninvasive method of
monitoring the percentage of hemoglobin (Hb) in the blood that
is saturated with oxygen. Sensors connected to the patientscontain two parts –LEDs and photodetectors. Red and infrared
LEDs are used as light sources. The red light has a wavelength ofThe heart 79

660 nanometers (nm), and the infrared light has a wavelength of
940 nm. These light wavelengths are passed through the skin,
often a finger tip, ear lobe, or foot (premature infants). Hemo-
globin in the blood both absorbs and re flects these wavelengths,
depending on the amount of oxygen that is being carried. Pho-todetectors measure the resulting intensities of light in the twowavelengths. The color of the blood changes with the amount ofoxygen in it. As the blood is pulsed past the light sources, theresulting signal varies –the blood flow creates a pulsating signal
that is directly related to the heart rate/pulse rate.
Note: Pulse oximetry readings do not indicate respiration
rate. While the respiration rate may influence oxygen saturation,the number of breaths per minute is not displayed during pulseoximetry monitoring.
This type of monitoring also shows the changes in saturation
as the heart beats. Because of this, pulse oximetry will indicateheart rate. In many cases, basic stable patients are monitored
using pulse oximetry. The sensor is very easy to apply; there areno sticky pads as required for ECG monitoring. A reusable pulseoximetry probe is shown in Figure 5.4. Patients do need toremove clothing or be awakened when the sensor is applied. In
addition, only one connection is needed. Lastly, the device itself is
very simple and relatively inexpensive. Heart rate determinedusing pulse oximetry requires no counting (as required for themeasurement of pulse rate by counting pulsations at the wrist),which can introduce human error.
In addition to the simplicity of heart rate measurements, pulse
oximetry is a very simple method to evaluate the quality of res-
piration activity (versus counting breaths, which may or may not
be successful in oxygenating blood). The quality of respiration canbe determined from the percentage oxygenation value reported by80 Introduction to Biomedical Instrumentation

these devices. Again, note that pulse oximetry does not measure
respiration rate. The device counts and displays heart rate and a
percentage value that indicates the percentage of hemoglobin (Hb)saturated with oxygen.
Most healthy people show a pulse oximetry of 95% or above
(indicating 95% of the hemoglobin is carrying oxygen). A reading
lower than 90% may be due to any factor that affects blood,
hemoglobin, and oxygen circulation in the body. Lower readingsm a ya c c u r a t e l yr e flect a patient problem or some situation that
prevents accurate saturation measurements. These may include:
▶Excessive bleeding
▶Lung problems, such as pneumonia
▶Cigarette smoking
▶Blood vessel problems
▶Respiratory disease or chronic obstructive pulmonarydisease (COPD)
Figure 5.4. Reusable pulse oximetry finger probe.The heart 81

▶Stress or pain
▶Hypothermia
▶Nail polish
Perhaps one of the best features of this type of monitoring is that
there is constant awareness of patient condition. Patients who
experience dif ficulties in effective respiration show changes in the
saturation readings immediately. In addition, changes in heartrate are immediately apparent.
Movement of the patient can be a problem in producing accurate
pulse oximetry readings. Movement might include something as
simple as shivering. A technique called Masimo SET (SignalExtraction Technology) is able to better reduce the inaccuracycaused by movement.
Many types of devices monitor pulse oximetry. For example,
this technique is often built into physiological monitors thatinclude blood pressure and temperature measuring devices.There are a wide variety of types of probe, the sensor that is
attached to the patient. Some are reusable and some are dis-posable. Usually, these are made to be quite durable.
STUDY QUESTIONS
1..What variables that represent a patient ’s vital signs are
commonly measured?
2..Make a table. In the first column, list the letters that represent
the parts of the ECG (P, Q, R, S, T), and in the second column,
describe the motion/action of the heart associated with thatpoint of the electrical signal.82 Introduction to Biomedical Instrumentation

3..Identify and describe the clinical difference between lead
and view.
4..What is the clinical bene fit of using more than two patient
connections to record the electrical activity of the heart?
5..Predict the resulting lead I waveform in a three-lead ECG if theRA is the positive connection and the LA is the negativeconnection. Use your knowledge of electrical connections topredict the result.
6..What are the augmented ECG leads?
7..Sketch a human torso. Label the patient ’s right and left sides.
Illustrate the locations of the electrical connections for a five-
lead ECG. Label each connection with the associated color.
8..Describe the patient information provided by pulse oximetrymonitoring.
9..Compare respiration rate data and pulse oximetry data. How
are they related to the activity of the lungs?
FOR FURTHER EXPLORATION
1..The ECG waveform is commonly used as a symbol ofhealth care. Locate examples of stylized representations
used in marketing. Why is this waveform such a popularsymbol?
2..Convert the heart rate vital signs information in Table 5.1 tohertz. Describe why it is uncommon to measure and recordhuman ECG data in hertz.
3..Research a common heart attack. Describe the underlyingphysiological changes that produce cardiac difficulties. Identifythe risk factors for a heart attack. Use the Internet to documentyour answers.The heart 83

4..The beeping heard in television shows is often a media attempt
to represent each pulse of a QRS complex. Why has therhythmic beeping become a symbol of life in the media?Identify hospital scenes where beeping is heard but no cardiac
leads are attached to the patient.
5..Patients who experience fibrillation do not have the straight-
line ( flat-line) waveform typically shown in the media. What
does a fibrillating heart waveform look like? Why does the
media represent it a different way?
6..Explore and describe a stress test. What does this entail? Whattype of monitoring is done during this test? What type of
patient has a stress test?
7..Suppose a clinician explains that a three-lead ECG monitorisn’t working. Lead III displays nicely but the other leads I and
II are very noisy –what could be the problem? Is it likely a
problem with the device?
8..The wires for the various locations on the patient havestandard colors. Draw a 12-lead ECG con figuration, identifying
the colors used in the various locations.
9..A common source of ECG monitoring problems occurs in partof the patient cable, which connects the patient and themonitor. A breakage of wire (under the insulation) occurs and
is not visible upon inspection. How could a BMET determine if
the patient cable has a fault? Why are breakages so common?TABLE 5.1. Heart rate ranges
Vital sign Infant ToddlerSchool-aged
child Adult
Pulse rate per minute (heart
rate) –values are listed in a
range for normal120– 160 90 –140 75 –100 50 –9084 Introduction to Biomedical Instrumentation

10..Explore this Welch Allyn booklet (http://www.iupui.edu/~bmet/
book/ECG_basics.pdf) that explores ECG recordings in depth.Summarize the major points.
11..Research electrical connections to measure ECG and the termunipolar lead. Why are these connections termed unipolar?What is the reference point for each augmented lead?The heart 85

6
Cardiac assist devices
LEARNING OBJECTIVES
1.describe de fibrillator waveforms and characteristics
2.define the term AED and describe why it is useful
3.describe cardioversion
4.describe assistive technologies such as LVAD, pacemaker,
implantable de fibrillator, heart-lung bypass, ECMO, cardiac
catheter, and IABP
87

Introduction
Technology is used to support heart function in numerous ways.
Perhaps the most common and well-known device is the defib-
rillator. In addition, the amazing life-saving powers of arti ficial
hearts and implantable devices capture the attention of thepublic and news media on occasion.
ACLS (advanced cardiac life support) is a detailed protocol to
provide life-saving cardiac care. BMETs may be involved in the
selection of technology and technical protocols used in a crisis. In
addition, BMETs may help establish training programs and
awareness for the technology involved in emergency response.
Defibrillators
Adefibrillator, which is often used in life-saving moments on
television medical shows, is a fairly simple device that delivers alarge amount of energy across a patient’ s chest when the heart is
not beating properly. When the heart is not beating with apattern, all cells are contracting at different times; this is knownasfibrillation. Defibs (as they are often called) in use today send
about 3,000 volts (V) –up to 20 amperes (A) –across a patient’ s
chest. ( Note: The amount of voltage and current vary tremen-
dously based on the patient ’s size and therapeutic settings.) This
large amount of energy causes all cells in the heart to depolarizeat once. This action may allow the SA node to resume functionand generate a normal electrical pattern. Sometimes the SA nodecan recover, but sometimes it cannot. The shape of the energy
waveform has evolved with experience. The Lown waveform was88 Introduction to Biomedical Instrumentation

the therapeutic waveform standard until recently. It looks like a
damped sine wave.
The biphasic waveform is the standard of care in de fibril-
lators today. It has both a positive and a negative component and
produces much better results more quickly. In addition, biphasicwaveforms are able to deliver results with less energy. Thewaveform is approximated in Figure 6.1.
Ad efibrillator is connected to a patient in a speci ficw a y .T h e
placement of the paddles or sticky pads on the chest delivers thebiphasic waveform in a way that mimics normal cardiac electricaldirection. One paddle is placed on the right side of the patient, nearthe clavicle. This paddle is often labeled “sternum. ”The other
paddle is placed on the left side of the patient near the ribs, below
the breast. This paddle is often labeled “apex. ”This con figuration
is often marked on the paddles (or sticky pads).
The proper functioning of a de fibrillator is vital to successful
patient care when a patient is experiencing cardiac problems.
Figure 6.1. Biphasic de fibrillator waveform (produces about 150 Joules of energy).Cardiac assist devices 89

BMETs ensure adequate testing procedures (including when the
device is not connected to an electrical outlet and is running onbattery power) and work to establish performance assurance
protocols. BMETs also measure the power output of de fibs to
ensure that the device settings match the actual delivered energy.
(Too little energy can fail to restart the heart, and too muchelectrical energy can injure the patient.) Test equipment usuallyincludes a simulated human body load.
Even though de fibrillators are excellent devices for restoring
cardiac electrical activity, they depend on the administration ofenergy in a very timely way. A general time frame suggests that forevery minute in fibrillation, a patient drops approximately 10% in
survival rate. Therefore, improving the time between the onset offibrillation and the application of the biphasic shockwave is a
critical goal.
Cardioversion is the process of shocking a heart at exactly the
right point in an ECG waveform. Cardioversion is required when
a heart is functioning somewhat and is not in complete fibril-
lation. The de fibrillator is capable of analyzing the ECG wave-
form from the patient to deliver the shock at the proper time.The shock is delivered immediately after the R wave peak.Essentially the physician applies the paddles to the patient,
pushes the shock button and nothing happens until the de fib-
rillator can deliver the energy at the right time. Cardioversion is a
commonly tested function to verify proper device performance.Specialized defibrillator test equipment can simulate the ECGwaveform needing cardioversion.
AEDs –automated external de fibs–are currently in the news
because these devices are now available in a wide variety of90 Introduction to Biomedical Instrumentation

places including in planes, in police cars, and with security
personnel. In O ’Hare Airport in Chicago, they hang on the wall
in glass cases (like fire extinguishers). The airport decided that
there should be a de fib within a one-minute fast walk from
anywhere in the airport. Basically, AEDs are the same as de fibs,
but they generally have no waveform display, use stick-onpatient pads rather than paddles, and calculate the power to bedelivered automatically. An important feature of AEDs is thepatient pads that check for ECG signals so that a patient who is
notinfibrillation will notbe shocked. Many of these units
provide audible instructions so that they can be operated by
someone without medical training. In addition, the devices havememory that stores the ECG waveforms of the patient andmakes them available to medical staff when the patient is trans-ported to a hospital. The American Red Cross has a wealth of
information about AEDs. Perhaps you have seen advertisements
for AEDs for people to keep in their homes, reserved foremergencies, like fire extinguishers. One type of AED is shown in
Figure 6.2.
Ultimately, the goal of making AEDs widely available is to
improve the survivability of cardiac fibrillation victims by
decreasing the time until de fibrillation can be applied. The
AEDs themselves must be self-diagnostic since testing isexpected to be performed by untrained people without testequipment.
Artificial hearts
Implantable hearts like the Jarvik 7 are unusual and are not
the typical choice for patients with heart problems, even thoughCardiac assist devices 91

their use is often highly visible in the press. Complete heart
replacement devices are often not the responsibility of most
BMETs except those with highly specialized training.
External temporary cardiac assist devices are used when the
patient has had signi ficant damage to the heart muscle. Blood is
diverted to an external ventricle giving the heart time to heal.
These are often used on a short-term basis when the patient isnot responding to other treatments and a transplant is neces-sary. Ventricle assist devices (VADs) and left ventricle assist devices
(LVADs) can be extremely costly and carry many associated
risks.
Figure 6.2. Automated external de fibrillator. (Photo courtesy of Medtronic.)92 Introduction to Biomedical Instrumentation

Pacemakers
Pacemakers can support the proper function of the heart to keep
regular electrical rhythm, or they can stimulate the heart only
when it does not beat properly. An example of a pacemaker isshown in Figure 6.3. In general, only BMETs with specializedtraining are involved in supporting pacemakers. There are several
types of pacemakers.
Figure 6.3. Implantable pacemaker (shown with leads). (Photo courtesy
of Medtronic.)Cardiac assist devices 93

▶Transcutaneous external cardiac pacing or transthoracic
external pacing (TEP) uses an external type of pacemaker
that uses electronic pads placed on the skin of the patient.TEP is often done in emergencies and for temporary measuresuntil an implantable pacemaker can be provided. A blend of
time of the pulse and amount of energy delivered is balanced
tofind good cardiac effect and yet make the process tolerable
for patients. Synchronous pacing is often used to supplementthe heart ’s own electrical activity.
▶Internal pacemakers are often as sophisticated as small
computers and are able to detect and correct electrical
abnormalities. When the pacemaker is in place, the control
circuitry and battery pack are located just under the skin belowthe clavicle. Wires are threaded through blood vessels into thecorrect cardiac position. These devices are able to respond topatient activity using ECG sensors on the case of the device. They
can store patient data for downlo ad wirelessly through the skin.
A variety of models assists patient s with their different electrical
conduction problems. Figure 6.3 s hows a three-lead pacemaker,
but two-lead pacemakers are also common.
▶External pacemakers are connected to the patient ’s heart
through internal wires but the electronics are locatedoutside of the patient. This method of pacing is often
used as a temporary measure (after surgery, for example) toassist the heart ’s own function.
Implantable defibrillators
Implantable de fibrillators, also called implantable cardio-
verter-de fibrillators (ICD): These devices deliver electrical94 Introduction to Biomedical Instrumentation

Figure 6.4. Heart-lung machine in an operating room.Cardiac assist devices 95

s h o c kt ot h eh e a r tw h e nfi brillation is detected. They are similar
to internal pacemakers in computer-like sophistication. How-
ever, they may not be needed to stimulate the heart very often or
at all. While they look very much like pacemakers, their purposeis quite different. They act like an insurance policy to restart aheart if necessary.
Heart-lung machines: These devices are also called cardiopul-
monary bypass and are commonly used during open heart surgery.
The machine oxygenates and pumps the blood for a patient.To minimize the damage that pumps can have on blood cells and
other blood components, roller pumps (which squeeze tubing to
move contents) and centrifugal pumps (which use centrifugal force to
move blood) are used. Blood is oxygenated, often using a membrane
that is carefully designed for gas exchange. The device includes ablood warmer as well. Figure 6.4 shows a heart-lung machine, andFigure 6.5 is a close-up of the pumps needed to move the blood.
Extracorporeal membra ne oxygenation (ECMO): Originally
exclusively used in the operating room (for surgeons to work
Figure 6.5. Heart-lung machine pumps.96 Introduction to Biomedical Instrumentation

Figure 6.6. Balloon pump.Cardiac assist devices 97

on the heart), heart-lung machines have a related device
called ECMO. This support is used on patients for longer
periods (days) rather than hours during surgery. Another term
for ECMO is extracorporeal life support (ECLS). Highly trainedBMETs are involved in the support of these devices.
Valve replacements: Human heart valves are replaceable. Com-
monly replaced valves include the aortic valve and the mitral
valve. Options for replacement include pig valves, which last
Figure 6.7. Balloon pump control panel.98 Introduction to Biomedical Instrumentation

between 7 and 15 years; mechanical valves, which are made of
metal and plastic; and human donated valves.
Intraaortic Balloon Pumps (IABP): These devices are often used
at the patient ’s bedside to assist the heart, allowing it to rest and
recover, especially after a heart attack (MI) or cardiac surgery. A
catheter with a balloon on the end is inserted into the femoral
artery and threaded inside the aorta. The balloon is in flated and
deflated, timed with the heart ’s rhythm, to improve coronary
perfusion and reduce the cardiac workload. Balloon pumps usehelium as the shuttle gas to in flate and de flate the balloon. The
balloon in flates during diastole to increase pressure, de flates just
before systole, which lowers pressure, making it easier for the heartto pump. The device is shown in Figure 6.6 and the control panelis shown in Figure 6.7.
STUDY QUESTIONS
1..Give an example of a patient condition that would require ACLS.
2..Compare the polarity of the electrical signal generated by the
heart by sketching the shape of the heart, labeling the SA and
AV node locations and then sketching the path of the electricalsignal. Discuss and describe how the biphasic waveform (andthe placement of the de fib paddles) mimics this electrical
conduction pathway.
3..Identify and de fine the conditions under which a de fibrillator
would be used on a patient.
4..Why is it vital for BMETs to regularly test the output of de fibs?
Why would careful calibration of the output energy beimportant?Cardiac assist devices 99

5..Identify community locations where AEDs should be placed to
ensure public safety.
6..Identify and describe the characteristics of patients who might
receive implantable de fibs.
7..Describe and de fine how IABP allows the heart to rest and
heal.
FOR FURTHER EXPLORATION
1..Use the Internet to investigate the history of de fibrillation.
Describe historical milestones and include the point at which it
became prevalent. How did de fibrillation change the care of
patients in cardiac arrest? Identify the latest majordevelopment.
2..Explore Web sites that describe AEDs. Characterize thesedevices. Describe the potential impact of prevalent and privateownership of these devices on the aging population. Policeoften carry AEDs in their cars since they often are the first
responders. How has this changed the survivability of afibrillating heart condition?
3..Use the Internet to explore the history of the arti ficial heart.
Summarize this history including signi ficant milestones. Who
is Barney Clark? How did his implant impact arti ficial heart
development? Is the use of a completely independent andimplantable arti ficial heart in the near future? Use the Internet
to research and document your opinion.
4..Heart transplant patients are often placed on LVAD inorder to support their health while they wait for a suitable100 Introduction to Biomedical Instrumentation

donor. Describe the support functions of this device in this
scenario. What restrictions do the patients have? How is thedevice powered? How long can a patient use a LVAD? What
complications can occur with the use of an LVAD? Use the
Internet to document and support your research.
5..Medtronic is a major manufacturer of implantable cardiacassist devices. Visit its Web site http://www.medtronic.com/tachy/patient/whatis_icd.html, which provides detailedinformation about ICDs. Summarize the function of an ICD.
6..Implanted devices of any kind can be in fluenced by the
magnetic fields (emi), which are produced from motors,
security equipment, and other devices. Summarize theinformation in this brochure, which discusses the impact ofemi on implanted devices: http://www.medtronic.com/rhythms/downloads/icd_en 199300962cEN.pdf.
7..How common is the use of implanted pacemakers? Whatfunctions and sensors do pacemakers have in order to control apatient’ s heart with the utmost of flexibility? For example, can
pacemaker patients run up a flight of stairs? Will their heart
rate rise? What routine maintenance is required for patientswith pacemakers? How long do the batteries in implanted
pacemakers last?
8..The medical staff person who controls the heart-lung machine
is called a perfusionist. What is his or her training? How mightBMETs work with perfusionists to support the safe andeffective use of heart-lung machines? Use the Internet tosupport your answers.
9..Describe the history of heart-lung machines. When were theyfirst used and how did they work? How have they evolved?Cardiac assist devices 101

10..Use the Internet to explore arti ficial heart valves. What are
they made of? How long do they last? Why would a
person need one? How has the design of valves evolved over
time?
11..Describe the functions and components of an intraaortic
balloon pump. Explore the cardiac bene fits of IABPs. Why are
they used? What therapeutic bene fits do they bring to patients?
Use the Internet to support your answers.102 Introduction to Biomedical Instrumentation

7
Blood pressure
LEARNING OBJECTIVES
1.describe the importance of blood pressure as an indicator of
patient health
2.describe mean arterial blood pressure
3.describe the common methods of blood pressure measurement:manual reading using a sphygmomanometer; automatedmethods using NIBP devices; and direct arterial
4.describe the purpose and use of a Swan-Gantz catheter
103

Introduction
Blood pressure is an important indicator of performance of the
human heart, lungs, and circulatory system. It is relatively easy to
obtain, and readings can be taken at speci fic time intervals to
track patient health. The peak and resting pressure of bloodwithin the arteries is the most commonly measured blood pres-sure vital sign. Blood pressure does rise and fall as the heart beatsand has a periodic waveform. The amount of pressure in the
heart can re flect the overall health of a patient and can be an
indicator of many diseases and conditions.
Indirect measurement methods
The most common noninvasive blood pressure (NIBP) meas-
urement method involves a blood pressure cuff and a stethoscope
(see Figure 7.1). The cuff is connected to a gauge that displays
pressure in the cuff. The cuff and gauge together are termed asphygmomanometer. The blood pressure cuff is usually placed
around the arm and in flated to pressures displayed on the gauge.
The manual technique involves a person who listens using thestethoscope to Korotkoff sounds. Listening to body sounds is an
auscultatory method of measurement. These sounds are related
to the equalization of pressures between the arm blood vessels andthe pressure in the heart. This technique has been in use for many,many years.
Sphygmomanometers can use air or mercury (Hg) within the
gauge to determine the pressure. The pressures are reported inmillimeters of mercury (mm Hg), even though most hospitalshave disallowed the use of mercury gauges.104 Introduction to Biomedical Instrumentation

Systolic pressure is the highest pressure in the heart and is
measured when the heart is contracting. Diastolic pressure, the
lowest pressure in the heart, occurs when the heart is filling. Blood
pressure typically is reported as a two-number ratio, systolic “over ”
diastolic pressure. Typical adult pressures are 120 mm Hg for
systolic pressure and 80 mm Hg for the diastolic pressure.
Figure 7.1. Blood pressure cuff and stethoscope.Blood pressure 105

There are limitations and sources of error in this indirect method
of measurement. Measurements can be compromised by
▶The inability of the observer to listen accurately and record
corresponding pressures accurately (ambient noise can be afactor)
▶A cuff that does not correctly match the size of the patient
▶The health of the patient –given that good limb perfusion is
necessary
Many clinical facilities use automated equipment to measure
blood pressure primarily because nurses may not be the persontaking vital signs, and the automated system is seen as morereliable. Many times, patients ’vital signs are recorded by a
medical assistant, like a nursing assistant, visiting each patient
bed at de fined time intervals. Figure 7.2 shows a physiological
monitor (NIBP, temperature) on a rolling pole. The automated
measurement technique is meant to allow people with limitedtraining to record blood pressure. As the nursing shortage haspersisted, assigning tasks such as measuring and recording bloodpressure to less-skilled workers has been a strategy for continued
quality of patient care. Using automated devices requires less
clinical experience and training.
Some staff may call all NIBP monitors Dinamaps since that
is a common brand. Many Dinamaps are mounted on rolling
poles to be moved from patient bed to bed. In addition to bloodpressure, most physiological monitors can assess other patient
variables like temperature and heart rate. Many NIBP devices are
designed to be moved from bed to bed by a nursing assistant torecord the vital signs (not just blood pressure) of patients atregular intervals (often every four hours).106 Introduction to Biomedical Instrumentation

Figure 7.2. Dinamap physiological monitor.Blood pressure 107

Automated devices use a blood pressure cuff like that used for
the manual method, but the cuff has no gauge and has a special
connector to attach to the NIBP device. However, these devices
detect changes in blood pressure using a method that does not listen
for Korotkoff sounds (auscultatory method) but instead detects tinypressure fluctuations from the arteries of a patient inside the blood
pressure cuff. First the device infl ates the cuff to a typical value
(which may be related to the previous blood pressure measurement).The device de flates the cuff in small increments, matching these
pressure oscillations to slowly de flate and determine the systolic and
diastolic pressures. This process is called the oscillometric method .
Direct invasive arterial pressure measurement
Blood pressure can also be measured directly by placing a catheter
into one if the patient ’s blood vessels. This may be done in the arm
and used when constant monitoring is critical for patient treat-ment decisions (patients in intensive care, for example). Thistechnique involves direct measurement of arterial pressure by
placing a catheter (small tube) in an artery (often radial or fem-
oral). The arterial catheter must be connected to a sterile, fluid-filled
system that is connected to a sensor. A pressure sensor, such as astrain gauge or piezoelectric crystal, can measure the pressure in thefluid-fi lled tubing. The resulting waveform is often displayed on a
monitor, as is shown in Figure 7.3. The bump in the pressure
waveform is called the dicrotic notch . It is a pressure change related to
the aortic valve closing. The timing of this notch can provide
clinicians with additional patient heart performance information.
Mean arterial blood pressure (MAP) is used in the clinical setting
to describe blood pressure as one number that represents the108 Introduction to Biomedical Instrumentation

average blood pressure in a patient. Typical values are approxi-
mately 100 mm Hg. Although the directly recorded blood pressurewaveform can be used to calculate this number, MAP is not usu-ally a mathematical average. There are several ways to calculateMAP, but, when monitoring a patient, it is generally done by theECG monitor using the geometric mean of the pressure waveform.
Many different pressures within the heart can be measured
directly using a Swan-Ganz catheter. To insert this device, a thin
tube is threaded into the pulmonary artery and measurements ofheart function are recorded when the catheter is in the properlocation. The catheter can assist in determining the pressure inside
the right side of the heart and in the pulmonary artery as well as in
establishing the cardiac output. These devices may remain con-nected to the patient in an intensive care unit as a constantmonitoring device for critically ill patients.
STUDY QUESTIONS
1..List and describe the advantages and disadvantages of NIBP
as opposed to the auscultatory method of blood pressure
measurement.
Figure 7.3. Typical blood pressure waveform.Blood pressure 109

2..Create a memory aid to identify systolic and diastolic
pressures. In typical blood pressure reporting, identify whichpressure is reported first and which is reported second
(as shown in Table 7.1).
3..Identify some of the advantages and disadvantages of continuousarterial blood pressure monitoring.
4..If mean arterial pressure was calculated using a strict mathematicalaverage, what value would the MAP have?
5..List and describe the physiological measurements that can be
determined using a Swan-Ganz catheter.
FOR FURTHER EXPLORATION
1..States have restricted or banned the use of mercury. Therefore,most blood pressure gauges do not contain mercury. Use the
Internet to explore how this ban affected hospitals as bloodpressure devices and thermometers were restricted. Describethe historical changes that have taken place. Re flect on the
continued measurement of blood pressure in millimeters ofmercury when mercury is a banned metal.
2..Use the Internet to record the medical de finition of hypertension
for adults. Most NIBP devices have limits of 300 mm Hg. Is itpossible that a patient could have a blood pressure higher thanthis value? If so, under what circumstances? How could bloodpressure be measured if it is greater than 300 mm Hg?TABLE 7.1. Blood pressure ranges
Vital sign Infant Child Adult
Blood pressure (mm Hg) 90/50 125/60 95/60 to 140/90110 Introduction to Biomedical Instrumentation

3..Blood pressure cuffs are sized to match the patient. Use the
Internet to explore the various sizes of cuffs. List the varioussizes that are commonly available. Describe the cuffs designed
for pediatric patients. Describe what happens when an obese
patient has his blood pressure taken with a cuff that is toosmall.
4..Blood pressure cuffs may be disposable or reusable. Discuss thecontamination issues that surround reusable cuffs. Are theyusually disinfected between patients? How is this commonly
used device involved in hospital-acquired diseases? Use the
Internet to support your answers.
5..Discuss the economic advantages of the use of all-in-onedevices that can easily be used to take the vital signs of patients.Identify the amount of training that is likely needed to operatea typical device. How does this training compare to the training
needed by a nurse? How does the hospital bene fit when it uses
all-in-one devices and low-paid staff to record vital signs? Are
there disadvantages related to this approach?
6..Examine the GE Web site that explores Dinamap technology,reading the pdf fileThe Dinamap Difference: A Guide to Our NIBP
Technology http://www.gehealthcare.com/usen/patient_mon_
sys/docs/DINAMAPDifference.pdf. Interpret and summarizethe information provided to explain in detail the process ofdetermining blood pressure using an NIBP device.
7..B l o o dp r e s s u r ei sr e l a t e dt ot h ev o l u m eo f fluid in the body.
Use the Internet to research and summarize the relationshipbetween hypotension and critica lly injured patients. Identify
and describe the situations that can cause hypotension.Identify and describe treatments that will improve bloodpressure.Blood pressure 111

8..Blood is pumped/pushed through the arteries. Blood is
returned to the heart in a passive system that uses the veins.Use the Internet to research and summarize the role of venous
valves in the return of blood to the heart. Identify conditions
where this return can be hindered.112 Introduction to Biomedical Instrumentation

8
Respiration and respiratory therapy
LEARNING OBJECTIVES
1.list and describe the components of inspired and
expired air
2.list and describe the important lung volumes
3.describe a spirometer
4.describe impedance plethysmography
5.describe apnea
6.describe capnography
7.list and describe the functions and settings of a ventilator
8.describe and characterize high-frequency ventilation
9.describe the method of connection between patients and theventilator
10.describe nebulizer, oxygen tent, and humidi fier
113

Introduction
The focus of this chapter is external human respiration .M o v i n g
air in and out of the lungs is external respiration and the focus
of technological interventions. The exchange of gases in thealveoli is part of internal respiration, but it is not essentialto this chapter. Here are some important facts related torespiration:
Make-up of air : 79% nitrogen, 20.96% oxygen, and 0.04%
carbon dioxide
Make-up of expired air : 79% nitrogen (unaffected by
respiration), 17% oxygen, and 4% carbon dioxide (human ’s
waste product)
It is important to know that the exchange of gas in the lungsoccurs in the alveoli.
Respiration measurements
Volumes of gases that fill the lungs during different moments in
respiration are important to BMETs since many machines try tofill those volumes. Amounts vary by the age, height, gender, andphysical condition of a patient.
Tidal volume : Breathing volume is about 500 milliliters (mL)
for an average adult male. This is the main value of importance.
Figure 8.1 shows a sine wave that illustrates the action of breathing
in and out. The tidal volume is moved in and out during eachnormal breath. When technology is used to support breathing,tidal volume is the amount of air that the machine must deliver.114 Introduction to Biomedical Instrumentation

When measuring breathing activity, most volumes are
measured using flow rates rather than actually measuring the
volume. However, spirometers are used to measure actual
patient lung volumes by respiratory therapists, often at the
patient bedside. More complex spirometers are electronically
controlled and provide a great deal of information about theperformance of the lungs of the patient. However, most auto-mated measurements (in ventilators, for example) are doneusing flow rates.
The typical adult respiration rate is about 12 breaths per
minute (see Table 8.1). Hyperventilation is breathing at a rate
that is faster than normal. Hypoventilation is breathing at a rate
that is slower than normal.
One important feature that is monitored is the effectiveness of
respiration –a patient may be breathing (air moving in and out) but
it is more important to know whether this activity is resulting in
appropriate oxygenation. Lab tests (often performed at the bedside
or in the unit) on patient blood can give such information. See
Figure 8.1. Respiratory volumes.Respiration and respiratory therapy 115

Chapter 13 for more information. Pulse oximetry is also used to
simply evaluate and measure the effectiveness of respiration.
Measuring respiration rates is important. This is often done
using transthoracic (across the chest) impedance measurements
(called impedance plethysmography ) since lung volume changes
with air –which is a dielectric and changes the impedance mea-
sured between two points. To do this, a small signal is passedthrough the ECG electrodes, which are located on the chest of thepatient. The resulting electrical change in impedance is measured.The changes in impedance (with changing lung volumes) can be
represented graphically over time as a respiration waveform.
Apnea is a prolonged pause in breathing. It is a common problem
in premature infants and can be life-threatening. Premature
infants are often monitored for apnea for months after they areborn. Frequently, pulse oximetry, which does not measure respi-
ration rate, is used to detect periods of apnea. This technique is
used because it is simple. The decrease in oxygen saturation (duringperiods without a breath) as well as detection of the pause inbreathing rate can trigger an alarm. Interestingly, episodes of apneacan be stopped by shaking the patient or tapping the incubator.
Capnography is the measurement of carbon dioxide concen-
trations in expired air. This technique evaluates the changes in
carbon dioxide values over time. This is often done duringTABLE 8.1. Respiration rate ranges
Vital sign Infant Child Adult
Respiratory rate –number of breaths per
minute (breathing) –values are listed in a
range for normal30–50 18 –30 8 –18116 Introduction to Biomedical Instrumentation

general anesthesia in surgery. Capnography can provide data to
monitor the patient response to anesthetic as well as the mech-anical ventilation techniques required to promote effective oxy-
genation. The Web site http://www.capnography.com provides a
very detailed explanation with some excellent graphics.
Mechanical ventilation
Long ago in medical device history, breathing was assisted usingchambers that enclosed the body to surround the chest withlower than atmospheric pressure (negative pressure) to make iteasier to breathe (termed negative extra-thoracic pressure ). These
chambers were called iron lungs . Iron lungs brought on prob-
lems by adversely affecting blood flow in the patient. Patient care
and movement were also tremendously hindered because thebody was confined to a chamber.
Mechanical devices today work in the opposite way –air is
pushed into the lungs (termed positive intra-pulmonary pressure ).
This does not mimic actual breathing. In normal breathing, air issucked into the lungs by moving the diaphragm.
Humans have ventilated other humans for centuries. There is
documented evidence from the 1700s of fireplace bellows being
used to force air into the lungs. Ventilation bags, which are similartofireplace bellows, allow one person to squeeze the device, forcing
air into a patient ’s lungs. They are commonly used for brief
periods when technology is not available or practical.
Ventilators , also called vents and respirators, are mechanical
devices that can either breathe for a patient or assist a patient ’s
breathing activities. A picture of one model is shown inRespiration and respiratory therapy 117

Figure 8.2. Ventilator.118 Introduction to Biomedical Instrumentation

Figure 8.2. They can be quite complex and are generally con-
trolled by microprocessors. Breaths may be delivered at a presetrate (for patients whose respiratory systems are injured or
intentionally paralyzed) if a patient goes too long without taking
a breath or whenever the patient initiates a breath.
Patients with some respiratory function can have a role in
ventilation with a ventilator. For example, the patient can initiatea breath and the machine will complete it. Careful monitoring ofthe patient’ s respiratory effort coordinated with device per-
formance is vital.
Physicians order particular settings for their patients on
ventilators, and respiratory therapists ensure that the equipmentmeets the doctors ’orders. Often BMETs work hand in hand with
the respiratory therapists since both spend a great deal of timewith the equipment.
Some of the settings related to ventilators include:
▶Respiratory rate –This setting determines how often the
machine delivers breaths.
▶CMV (continuous mandatory ventilation) –In this mode,
ventilation occurs at regular intervals. This is often used when
patients cannot initiate breaths on their own. Common rates are
10–15 breaths per minute for an adult. Note that this frequency
in hertz (breaths per second) is less than 1 Hz.
▶SIMV (synchronized intermittent mandatory ventilation) –This
setting delivers occasional brea ths produced by the ventilator,
for patients who may be breathing on their own but not often
enough to adequately oxygenate themselves. The breaths are
timed to complement the breathing pattern of the patient.
▶CPAP (continuous positive airway pressure) –This feature,
which makes initiating a new breath easier, is often used as aRespiration and respiratory therapy 119

therapy that can be provided at home. This assistance is
provided for patients who are breathing on their own butneed some assistance.
▶PEEP (positive end expiratory pressure) –For patients who are
completely machine dependent, this setting is similar to CPAP.
▶Oxygen concentrations –This measurement ranges from
normal air percentages to 100% oxygen.
▶Sensitivity –This setting determines how much effort is
required for a patient to trigger a breath. It is useful when
weaning patients from ventilator dependence.
The amount of air that is put into the lungs is important.However, most machines determine the amount of air not by
measuring the volume but by measuring the flow rate and
calculating the volume.
Ventilators are life-sustaining devices, and their reliable and
consistent performance must be assured. Alarms and backup
systems are integral to ventilation design to warn of unintended
behavior or device failure. Ventilators can often function brie fly
on battery power. In addition, they are often connected to out-lets, which ensures emergency power in the event of an outage.
High-frequency ventilation
High-frequency ventilation (HFV) was introduced in the early1990s for use in the neonatal intensive care unit. There are
two main types: the high-frequency jet ventilator and the high-
frequency oscillator ventilator (HFOV). The goal of the HFV is
to improve alveolar stability, oxygenation, and ventilation with
decreased lung damage related to pressure and volume. The120 Introduction to Biomedical Instrumentation

lungs stay in flated while both volume and pressure changes
associated with continuous forced opening and passive closing of
alveoli are avoided. With the oscillator ventilator, breaths are
delivered by a vibrating diaphragm that provides for both a
positive inspiration and active exhalation.
The settings for the HFOV differ from the conventional
ventilator. Settings are:
▶MAP (mean airway pressure) directly affects oxygenation byimproving lung volume.
▶Delta pressure (Delta-P) is the oscillatory amplitude, and, asthe difference between the peak and trough pressures, it
directly determines tidal volume. Delta pressure is used to
control the carbon dioxide (CO
2)–increasing the Delta-P
will cause the CO 2to drop; decreasing the Delta-P will cause
the CO 2to rise.
▶Hertz is the expression of breath rates: Hz is commonly setat 10 –15, which is 600– 900 breaths/minute. Adjusting the
hertz will also change the tidal volumes.
Caution: This is a relatively new technique, and some older texts
and Web sites may de fine high-frequency ventilation as any
ventilation greater than hyper-respiratory rates, say 60 breathsper minute. This de finition is notthe same as HFV.
Ventilators are most commonly connected to the patient via
anendotracheal tube through the mouth. The tube is curved to
match human anatomy. Many endotracheal tubes contain an
inflatable cuff at the end to make a seal against the sides of the
trachea, as shown in Figure 8.3. The cuff is in flated with air from
a syringe. A laryngoscope is used to guide the insertion of the
endotracheal tube. These devices are very common in hospitalsRespiration and respiratory therapy 121

and can be lighted to guide the insertion of the endotracheal
tube. A second type of ventilator connection, which goes throughthe neck, uses a tracheostomy tube (sometimes called a trach).
The tracheostomy is typically used for patients who will bedependent on a ventilator for a long time.
Other respiratory equipment
The respiratory therapy department uses many devices that arenot ventilators. These include oxygen tents and masks, humidi-
fiers, and nebulizers.
▶Oxygen tent –This device is usually made of plastic and is
placed over a bed in order to maintain an oxygen-rich
environment. Temperature and humidity may also becontrolled in the tent environment. Oxygen tents areoften used in pediatric units so that patients may movearound.
Figure 8.3. Endotracheal tube.122 Introduction to Biomedical Instrumentation

▶Humidi fier–This device increases the humidity of the air
and can be used in many situations. Humidi fiers may be
part of ventilators and incubators, among other devices.
▶Nebulizer –This device is able to create a medication mist
that can be added to air to be inhaled by a patient.
Extracorporeal membrane oxygenation (ECMO) is a method
of oxygenating blood outside of the patient ’s body. Similar to a
heart-lung bypass, which is do ne during open heart surgery,
this device consists of a pump to move the blood, warmers and
filters, and filters for the blood. A newer term for this device is
extracorporeal life support (ECLS). This is a support method to
help the lungs of neonates mature or heal. It is often done as a
last resort when other mechanical techniques have failed. Aconnection is made directly from the patient ’s heart to the
ECMO machine. Although more commonly used for infantpatients, some children and adults are connected to ECMO
devices.
STUDY QUESTIONS
1..Using Figure 8.1, compare the total volume of air in the lungs
and the relative amount of air that is moved during normal
respiration.
2..What is the main component of the air humans breathe? Is it a
gas that is used by the body during the respiratory process?
3..Describe why it is much more informative to know about thequality of respiratory activity than the respiratory rate.
4..List and describe some of the technologies and tests used to
monitor patients who have breathing support.Respiration and respiratory therapy 123

5..Describe how pulse oximetry can be used to monitor newborn
babies for apnea.
6..Describe how CPAP can assist patients in the initiation of a
new breath.
7..Describe the major differences between common ventilators
and high-frequency ventilators.
FOR FURTHER EXPLORATION
1..Use the Internet to explore and document the volume of lungsin various patients including premature infants, toddlers, andathletes. Create a table showing the various lung volumes fordifferent types of patients. Identify and compare the smallestand largest values. How do these values compare to the
assumed average value of 500 mL?
2..Many people have CPAP machines at home. Use the Internet
to explore and document how these devices work. Identifythe parts of these systems. Describe how they bene fit
the user.
3..Explore and describe the historical use of the iron lung. This
was desperately needed for polio patients. Research and
document the relationship between polio and the iron lung.How did it assist the breathing of patients? How effective wasit? Identify its side effects. Briefly explain the dramaticimprovement in breathing support that was experienced withthe invention of the ventilator.
4..Calculate the breathing rate of a typical ventilator in hertz.Compare the breathing rates (in hertz) for a typical adultventilator with that of high-frequency ventilation. Discuss thissignificant magnitude of difference.124 Introduction to Biomedical Instrumentation

5..Use the Internet to explore, research, and identify the major
components of an ECMO system. What are the primaryfunctions of most ECMO systems? How do these functions
differ from those of cardiopulmonary bypass?
6..Describe how ventilators can affect a patient ’s speech. What
techniques can be used to allow patients to speak?
7..Breathing circuits are made up of tubing that connects patients
to ventilators and anesthesia delivery systems. What are thecomponents of breathing circuits?
8..Ventilators shown in the media often show a piston (a blackaccordion device) moving up and down (it makes a very nicevisual representation of mechanical support). Often, an easilyidenti fiable noise (cyclical, piston sound) can be heard in hospital
scenes even when no ventilator is being used. These volumeventilators are generally no longer in use. Use the Internet to find
a photo of a Puritan Bennett MA1. This device used to be state ofthe art and was extremely common. Describe the features of thisdevice. Search the Internet for the Puritan Bennett 840, thecompany ’s latest ventilator. Compare the two devices.
9..To understand breath delivery by ventilators, visit the PuritanBennett Web site http://www.puritanbennett.com/_Catalog/
PDF/Product/ABCsSmarte%20BreathDeliveryClinicalBrochure.
pdf, and look for the pdf fileClinical Brochure: ABCs of Smarter
Breath Delivery . Summarize the information in this brochure.Respiration and respiratory therapy 125

9
The brain and its activity
LEARNING OBJECTIVES
1.list and describe basic neuroanatomy and physiology terms
2.list and describe EEG characteristics (four waves)
3.describe depth of anesthesia monitoring
4.describe ICP monitoring
5.describe a CSF shunt and identify its functions
127

Introduction
Measuring the activity and function of the brain is more com-
plex than measuring the electrical activity of the heart. Signals
from the brain are more rando m and have only recently been
translated into speci fic applications. Even though brain signals
can be extremely useful in patient assessment, in general,measuring the function of the brain is far less common thanother technology-facilit ated patient care tools.
Review of neuroanatomy and physiology
Here is a brief review of basic neuroanatomy and physiologyterminology.
▶Neuron –This is the most basic cell associated with the
brain.
▶Brainstem –This portion of the brain controls life-
sustaining functions.
▶Cerebellum and cerebrum –These major parts of the brain
control various body functions and memory.
▶Ventricles of the brain –These spaces within the brain are
important because implants and monitors often involve
these areas.
▶Spinal cord sections –The spinal cord includes the cervical,
thoracic, lumbar, and sacral regions.
▶Cerebral spinal fluid (CSF) –This fluid is very important
because it cushions the brain and can be monitored to assess
brain health.128 Introduction to Biomedical Instrumentation

Electrical activity in the brain
Electroencephalography (or electroencephalogram)
The electrical signals from the brain can be measured using many
electrodes on the scalp. EEG signals created inside the brainare complex and relatively random. Measured at the scalp, EEGamplitudes are very small, in the range of microvolts. Speci fically,
EEGs are used to:
▶Evaluate brain lesions
▶Identify epilepsy
▶Evaluate mental disorders
▶Assess sleep patterns
▶Evaluate brain responses to stimuli
Patterns and information are more dif ficult to obtain from an
EEG than from an ECG. Nevertheless, tests are often performedthat evaluate the EEG waveform in response to an input likelight or sound. Since data can be gathered from many people, atypical EEG response can be predicted and compared to the
response of a particular patient. Noise, motion artifacts, and
ECG signal interference can present some major issues becauseEEG waveforms appear at the scalp in such low voltages.
Brain signals, which are grouped based on frequency, are
divided into alpha, beta, theta, and delta waves. Different signalsare prominent depending on the age and activity of the patient.
▶Alpha –7.5–13 Hz; present during rest and relaxation.
▶Beta –14 Hz and higher; present for patients who are alert
and awake. These waves have the lowest amplitude.
▶Theta –3.5–7 Hz; normal for awake children.The brain and its activity 129

▶Delta –3 Hz or below; common during sleep and in infants.
These waves have the highest amplitude.
Evoked potential testing
When an EEG is being evaluated, a common test is to measurethe electrical activity of the brain in response to a stimuli. Someexamples of stimuli include sound or a flash of light. When this
test is performed, the EEG will be examined for the time the braintakes to respond and the location of the response.
Depth of anesthesia monitoring
The EEG can be used to determine the level of sedation of a patientduring anesthesia. This noninvasive method analyzes the EEG usingmathematical algorithms. The analysis technique was created usingdata from many test subjects who underwent anesthesia. The
mathematical algorithm used to analyze the EEG from three EEG
leads on the forehead of the patient varies by companies. Figure 9.1illustrates the placement of leads on the forehead. A popular method
of analysis is BIS,which stands for Bispectral Index. The monitoring
produces a numerical score of 0 (dead) to 100 (fully awake). Thismonitoring allows careful control of sedation and more precise
delivery of medication. The BIS m onitoring technology is used by
multiple manufacturers.
Intracranial pressure (ICP) monitoring
The ICP is essential in the treatment of brain-injured patients.Pressure can be monitored under the skull or in the ventricles.
The pressure is normally about 1 –15 mm Hg in adults (20 mm Hg
is usually considered the limits of safe pressure) and is typically
measured in the ventricles. ICP monitoring can be done in severalways.130 Introduction to Biomedical Instrumentation

▶Subdural/subarachnoid pressure can be monitored by
attaching a bolt to the skull. The data may not be veryreliable, but the ventricles are not entered so infectionproblems are avoided.
▶An intraventricular catheter can be inserted through thefrontal lobe of the brain and into the lateral ventricle. Thecatheter can be used to monitor the ICP as well as to drain CSF.
Figure 9.1. BIS leads on a patient.The brain and its activity 131

▶Afiber-optic ICP sensor located at the end of a catheter
can be placed in the patient’ s parenchyma (Camino ICP
monitoring is the most common method).
Calibration/zeroing is required for these transducers.
Brain perfusion
Understanding and evaluating the blood flow to the brain is a
useful diagnostic tool in the evaluation of patient condition.
Cerebral perfusion pressure (CPP) is the intracranial pressuresubtracted from the mean arterial blood pressure. However, as adiagnostic tool, cerebral blood flow(CBF) is a better indicator of
neurological health. Currently, this is not easy to measure. Some
emerging techniques include xenon-enhanced computer tomog-
raphy (XeCT), positron emission tomography (PET) scans, andsingle photoemission computer tomography (SPECT). Thermaldye-dilution can be used but is not used commonly at the bedside.
EEG monitoring
This type of EEG testing can be done at the patient ’s bedside to
diagnose conditions related to coma and seizures and to evaluate
recovery. There are quite a few problems with this type of testingbecause the environment in the intensive care unit is not con-trolled as well as that in the EEG laboratory. Some sources ofdifficulties include:
▶60-Hz noise
▶Ventilator, IV pump, and vibrating mattress artifacts
▶Movement and contact by nurses and therapists
▶Patient movement
▶Sweat and muscle artifacts
▶Wounds or burns on the patient ’s scalp that limit access132 Introduction to Biomedical Instrumentation

Sleep studies
EEG monitoring is used extensively to assist in the diagnosis andtreatment of sleep disorders and sleep-related respiratory dif fi-
culties. Patients are connected to an EEG recorder and other
monitoring devices and asked to spend a night in the hospital for
observation. Sleep study rooms are monitored by technicianswho can record data and make adjustments to patient equip-ment such as CPAP settings. Figure 9.2 shows a patient ready forobservation. The data from the leads connected to the patientwill be processed on an EEG recorder. Figure 9.3 shows one type
of recorder. Figure 9.4 shows a homey sleep lab room where
observation can take place.
Cerebral spinal fluid shunts
Cerebral spinal fluid shunts are used to transfer excess fluid from
the ventricles into the abdomen (or other areas). When the brain
has structural anomalies, CSF shunts are implanted to avertbuildup of cerebral spinal fluid. These devices are essentially
plastic tubing that drains fluid from the brain (using gravity)
into other parts of the body where the CSF can be absorbed.
STUDY QUESTIONS
1..Compare the amplitude of an ECG and the amplitude of an
EEG. Identify difficulties that may be encountered because of
the small EEG amplitude.
2..Evoked potential testing can be used to test the hearing of
infants. Describe how using sound and evaluation of brainwaves could be used to evaluate hearing in nonverbal infants.The brain and its activity 133

3..Describe the advantages of using de pth-of-anesthesia monitoring
using EEGs.
4..The skull is rigid so brain swelling is dangerous because, unlike
swelling in other parts of the body, the organ has limited space.
Figure 9.2. Patient connected to EEG leads.134 Introduction to Biomedical Instrumentation

Describe pressure monitoring and how this can be bene ficial
for patients.
5..Assessing the brain activity of unconscious patients is helpful.
Discuss some of the difficulties in measuring the electricalactivity of the brain.
Figure 9.3. EEG recorder.The brain and its activity 135

FOR FURTHER EXPLORATION
1..Use the Internet to obtain a drawing of the vertebral column
and spinal cord. Identify the cervical, thoracic, lumbar, andsacral regions. Sketch this and be able to identify the regions ofthe body that the various spinal nerves control. Which is closer
to the brain, T3 or L1? Spinal cord injury can result in
paralysis. Research and document the types of spinal cordinjuries (and at what level) that result in quadriplegia.
2..Epidural anesthesia, commonly used in the surgical delivery ofinfants, is a technique of applying anesthetic to an area aroundthe spinal cord. Research and document the process used in
this technique, including the location of medication delivery
along the cord.
Figure 9.4. Sleep laboratory patient care/observation room.136 Introduction to Biomedical Instrumentation

3..Create a table that identi fies the four types of EEG waves and
their amplitude and frequency characteristics. Include, within
this table, details related to the conditions under which the
particular waveform is usually present.
4..Use the Internet to research and document the portions of the
brain that generate different EEG waves.
5..Investigate and document four pathological conditionsthat can be re flected in abnormal EEGs. Include epilepsy
and dementia and describe the symptoms of the condition,
how the EEG is altered, and the possible treatment con-
siderations.
6..Research and document the discovery of EEG waves. Includewhich wave was identi fiedfirst and how this was accomplished.
Cite your references.
7..Investigate and identify the equipment used to deliver evoked
potentials. What types of stimuli are used? How is this
information useful?
8..Some neurological research involves the measurement ofelectrical activity directly on the surface of or inside the brain.Research, document, and describe this technique, which istypically called intracranial EEG. Identify the purpose of this
process.
9..The muscles of the body generate voltage, and this can interfere
with the measurements of EEG waveforms. Movement of theeyelids or tongue can cause interference. Research and summarizethe methods to obtain EEGs from patients. Speci fically discuss
what techniques are used to eliminate the effect of muscle
voltages as interference.
10..Before the use of depth-of-anesthesia monitoring (which provides
quantitative data), anesthesiologists relied on qualitativeassessment methods. Research and document these qualitativeThe brain and its activity 137

techniques. How is a numerical system an improvement in
anesthesia delivery?
11..Brain Computer Interface (BCI) has gained attention in the press
recently. Explore this technique to circumvent damaged spinal
cords or sensory organs. Describe the technical requirements andprovide some examples of BCI applications.138 Introduction to Biomedical Instrumentation

10
The intensive care unit
LEARNING OBJECTIVES
1.identify and describe the characteristics of an ICU and an ICU
patient
2.identify and describe the types of monitoring that occursin ICUs
3.identify and describe the major types of ICUs and the supporttechnology used within them
4.define and describe medical telemetry and WMTS
139

Introduction
Patients who are very ill or in serious condition will usually be
found in the intensive care unit (ICU). Although these patient care
areas may be called various names, they have some similar qual-ities. Generally, intensive care units have a very large amount oftechnology involved in patient monitoring and treatment. Tech-nical staff who work in this area need to understand the charac-teristics and special needs of ICUs.
Many hospitals in the United States have their own way of
organizing and providing intensive care. For example, somehospitals do not separate surgical and medical patients. Somehospitals include transplant patients in their medical units,whereas others send transplant patients to the surgical floor,
and still others have stand-alone transplant intensive care units.
It is virtually impossible to address all the variations in this
chapter. However, the issues important to intensive-carepatients and staff who care for them transcend the hospital-defined categories.
Characteristics of intensive care units
Some smaller or rural hospitals may not provide a high level ofintensive care; consequently, patients who need intensive care aretransferred to other hospitals. Here are the main characteristics
of ICUs:
▶Patients are very ill.
▶Patients have a high mortality rate.
▶Patients may not be conscious or mobile.140 Introduction to Biomedical Instrumentation

▶Most patients are restricted to bed.
▶There may be limited day/night cycles.
▶Physiological monitoring is constant.
▶Each staff member is assigned to only a few patients.
▶Units may be noisy.
▶Patient may be in an ICU for weeks or months.
▶There are restrictions about who can enter a patient room
and when.
▶Patient must be monitored very closely.
▶Tubes attached to patients include feeding tubes, endotrachealtubes, IVs, and urinary catheters.
▶Ventilators –patients may be dependent on technology to
get air into and out of their lungs
Within the ICU, monitoring often consists of:
▶The heart ’s electrical signals (often with either a three- or
five-lead ECG)
▶Noninvasive blood pressure
▶Invasive blood pressure that uses an arterial line (a catheterthat enters an artery)
▶Blood gases –from a blood sample to evaluate the
amount of dissolved gases it contains (often done at thebedside)
▶Respiration rate
▶Pulse oximetry –a noninvasive method of determining the
amount of oxygen carried in the blood
▶Temperature
▶Chemistry of the blood –from blood samples to
evaluate characteristics such as pH (often done at the
bedside)The intensive care unit 141

Patients generate a great deal of data that is often networked and
stored for analysis later. Physicians can use trends in patient dataover time to better diagnose and treat patients.
Types of intensive care units
Special care units where the patients and the staff differ from therest of the hospital go by many names. A list of these special care
units follows; however, be aware that sometimes individual
hospitals will de fine the same letters differently.
Cardiac care unitPatients in the cardiac care unit (CCU or CICU) may be
recovering from a heart attack or bypass surgery. They are typ-
ically older and may have a high level of mortality. Additionally,
they may have many characteristics of the elderly, includingslower healing, general physical limitations, and less mentalacuity. Cardiac patients may need to be resuscitated far moreoften than the general patient population. Resuscitation usually
involves de fibrillation. Code carts , which contain defibrillators
and medications to treat nonperforming or underperforminghearts, are located in almost every room.
Equipment frequently found in the CCU includes balloon
pumps and external assist devices for the heart. Balloon pumpsare inserted into the descending aorta to help the heart function,which allows a patient ’s heart to rest and heal. The balloon
inflates during diastole to increase pressure. The balloon de flates
just before systole, creating a void, thereby lowering pressure andmaking it easier for the heart to pump. Cardiac assist devices,such as left ventricular assist devices or ventricular assist devices142 Introduction to Biomedical Instrumentation

are essentially external pumps that can help the heart heal or
support a patient until a transplant is found.
Pacemakers may also be used to support patients in the CCU.
They may be temporary and external. Pacemakers are described inChapter 6.
Neonatal intensive care unit
Patients in neonatal intensive care units (NICU , often pro-
nounced as one word: nick-you ) are typically between 23 and 40
weeks of gestation (normal pregnancy is 40 weeks) and can weighfrom around a pound to more than 10 pounds. The small sizeand critical condition of these infants can be shocking when aBMET first visits the unit. Patients may have very red and
translucent skin, need massive support for bodily functions, andbe extremely small. Babies are divided into two large groups:
those who are born before term and have complications that
stem from their early birth and those who are born at term.Patients in the second group either have disorders or compli-cations developed during the pregnancy or complications thatwere a result of the birth process.
Neonates need a very controlled environment in order to
allow organs and systems to grow and mature. There are gener-ally two types of environments used, incubators and warmers.
▶Incubators (also called isolettes) are small beds completely
enclosed by Plexiglas. Doors in the incubator allow cliniciansaccess to the patients while minimizing heat loss. The airinside is usually warmed and humidi fied; it may also be
oxygenated. An incubator is shown in Figure 10.1.
▶Warmers are open beds that have a radiant heater and
bright lights above the uncovered patient bed. A sensorThe intensive care unit 143

placed on the baby controls the temperature provided by the
heater above. The patient bed is usually x-ray transparent sothat x-rays can be taken without moving the patient. Anexample of a warmer is shown in Figure 10.2.
Some speci fic therapies that are most commonly used on
NICU patients include ECMO (see Chapter 8) and treatment forjaundice. Infants may have hyperbilirubinemia, which is jaundice .
The treatment for this is called phototherapy, which involves
exposing the patient to a speci fic wavelength of light (in the blue
region). Phototherapy treatment usually uses the wavelength oflight that can travel through the skin and destroy the hazardouscompounds in the blood. Before the introduction of fiber-optic
Figure 10.1. Incubator.144 Introduction to Biomedical Instrumentation

Figure 10.2. Infant warmer.The intensive care unit 145

blankets, it was common to see banks of blue light bulbs shining
down on the patients. The blue lights were, however, difficult forstaff (they can cause nausea) and could mask the condition of
patients. The use of phototherapy blankets is less intrusive to the
NICU. The measurement of light intensity at the patient positionis a critical step in the assurance of proper dosing of light. Lightmeters that measure in the correct wavelength (425– 475 nm) can
assess the light intensity. Fluorescent bulbs do decay in theirlight output, and BMETs may test at regular intervals to deter-
mine replacement frequency.
Pediatric intensive care unit
Pediatric intensive care units (PICU , often pronounced as one
word: pick-you ) are speci fically for children. Children are not just
smaller adults. Not only are their organ systems growing and
changing, but the patients may be unable to be cooperative or
answer questions. PICU patients are generally aged from new-born through adolescence (although some hospitals use age 1 asthe youngest patients in pediatrics). Generally, the infants in aPICU may have been discharged at birth and then returned to thehospital. Patients who are in pediatric intensive care units may be
recovering from surgery, have a serious illness, or have experi-
enced trauma (such as drowning or other accidents). Manypatients present with complex medical issues that involve severalorgan systems.
Medical intensive care unit
Patients in the medical intensive care unit (MICU) are seriously
ill for medical reasons. Some examples include asthma, pneu-
monia, tuberculosis, and AIDS, but MICU patients also mayhave experienced trauma. The trauma a patient might have146 Introduction to Biomedical Instrumentation

experienced varies greatly depending on the institution and
its surrounding community. For example, gunshot woundsand drug overdoses may be common in an urban setting,
whereas snake bites and scorpion stings might be common in
another. Patients in this unit have a wide variety of complex
health issues related to envir onment and disease, but they
generally exclude speci fic and isolated issues with the cardiac
and nervous system.
Surgical intensive care unit
Generally, patients in the surgical intensive care unit (SICU) are
post-operative. Some may be critically ill as a result of surgery;others may be recovering from a surgical procedure and requirethe monitoring the unit provides. Hospitals may includeneurosurgical or cardiovascular surgical patients in this group,
and transplant patients may be included as well. Examples of
surgical procedures include amputations, gastrointestinal pro-cedures, peripheral vascular surgery, orthopedic procedures, andurologic surgery.
Many times, recovery from surgery is complex due to a
patient ’s preexisting conditions such as diabetes or heart disease.
Wound healing and closure is vital for patient recovery. Unfor-tunately, promoting healthy healing is not always easy, especiallyfor patients with multiple medical issues.
Other types of ICUs
Burn patients may be cared for in a burn ICU. Burn patients may
be treated with hyperbaric therapy. This approach to wound
healing uses chambers that enclose the patient to increase theamount of oxygen carried in the blood. This is accomplished byincreasing the pressure inside the chamber.The intensive care unit 147

Patients who have neurological issues may be treated in a
neuro ICU. Much of the equipment in this unit is described in
Chapter 9, which explores the brain.
Support common for many patients
Deep Vein Thrombosis Prevention: A patient’ s inability to move
may contribute to the development of deep vein thrombosis
(DVT). DVTs may become life threatening if the thrombus travels
to the lungs, causing pulmonary tissue death. The use ofsequential compression devices is widely accepted in the ICU patient
population to assist in the prevention of DVTs. These devicescompress the feet or legs in a rhythmic way.
Nutrition: Patients who are critically ill need to consume calories,
but they may be unable to do so because they are unconscious,
injured, or lack physical strength. There are two sources forproviding calories. Enteral nutrition provides calories through a
tube into either the stomach or the intestine. A naso-gastric tubeis often used to deliver the liquid nourishment. A tube passing
through the nose may be a temporary feeding pathway; however,
long-term support can be provided through a port in theabdominal skin, directly connected to the digestive tract.Nutrition may also be delivered via total parenteral nutrition(TPN). Parenteral nutrition (hyper-alimentation) bypasses the
digestive system. This delivers a glucose and fat emulsion with
other nutrients directly into the vascular system. An IV pump
(feeding pump) is usually used to deliver this fluid.
Renal Support: Kidney dialysis replaces the functions of a
normal kidney. Both water and waste products normally filtered148 Introduction to Biomedical Instrumentation

Figure 10.3. Dialysis machine.The intensive care unit 149

by the kidney can be removed from the patient’ s body. Kidney
dialysis machines filter blood using a semipermeable membrane.
(See Figure 10.3.)
Patient Care Beds: In the past, patient care beds were devices
with a mattress and a hand crank to raise/lower the head or foot.
Now, beds have microprocessor controls that can monitorpatient movement and inflate and de flate the mattress to alle-
viate pressure points. Hospital beds may have tiny holes in the
covering to circulate air around patients. In short, patient beds
are quite complex.
Telemetry
Patients who may be improving but still need constant monitor-ing may be allowed to get out of bed and walk around usingtelemetry. The physiological signals of the patient are transmittedover radio frequency waves (this technology was initially createdfor astronauts). The patient wears a transmitter, and the signalsare sent to a central monitoring station (often at the main desk of
a patient care area). The frequency that carries the signals has been
challenging in a world where speci ficb a n d sa r es e ta s i d ef o r
applications by the Federal Communications Commission (FCC).Recently, a Wireless Medical Telemetry Service (WMTS) frequencyband was designated. The FCC has designated the AmericanSociety for Healthcare Engineering as the medical telemetry fre-
quency coordinator. Visit http://www.ashe.org and view its telem-
etry links. Originally, hospitals used 450 –470 megahertz (MHz)
until a test of Digital TV (DTV) stations in Dallas, Texas, in 1998.There was interference, and this began a discussion of setting aside150 Introduction to Biomedical Instrumentation

as p e c i fic spectrum for medical telemetry. Now speci ficb a n d sh a v e
been dedicated to WMTS 608 –614 MHz, 1395 –1400 MHz, and
1427 –1432 MHz to limit interference.
STUDY QUESTIONS
1..Create a table where the rows are the different types of intensive
care units and the columns are patient characteristics and
specialized equipment. Briefly summarize information speci fic
to intensive care units to complete the table.
2..Make a list of typical equipment found in a typical, general ICU.
3..Identify and describe the technologies that can be used to assist
neonates with temperature regulation.
4..Describe and compare the pressure inside the chamber of an
iron lung (Chapter 8) and the pressure inside a chamber
designed to promote wound healing.
5..Compare and contrast the two methods of nutritional support.
6..Describe the bene fits of telemetry to the patient.
7..Describe the types of physiological information that might begathered over time and used by medical staff to support patient
care decisions.
FOR FURTHER EXPLORATION
1..The Society of Critical Care Medicine offers an excellent Website that provides a virtual tour of an ICU room. The site is
http://www.icu-usa.com/tour/icu_room_tour.html. Visit thisWeb site to see the components of an ICU room. Describeand summarize your tour.The intensive care unit 151

2..Continuous cardiac output (CCO) is a common CCU patient
technology. Research and describe this technique, which uses aSwan-Ganz catheter. Describe how this technique is able to
quantify the performance of the heart. Document typical
patient measurements obtained using this technique.
3..For neonates, gestational age identi fies how long the infant
spent in utero . Gestational age may be a predictor of health and
technological support needs. Use the Internet to research anddocument the relationship between viability and gestational
age. What is the current minimum pregnancy duration that
results in a live infant birth? Document how it has changedover time.
4..Birth weight can be a predictor of infant viability. Research anddocument the weight associated with very-low-birth-weight(VLBW) babies. Use the Internet to explore, research, and
document the speci fic technologies involved in the care of very-
low-birth-weight babies. Focus on equipment and devices
(avoiding lengthy and complicated medical interventions).
5..The treatment for hyperbilirubinemia involves the exposure tothe blue wavelengths of light. Use the Internet to research thismedical condition and the technology used to treat it. Why do
newborns have this condition? What does light shined through
the skin accomplish? What wavelength is therapeutic? Whattechnology is used to provide light therapy? Why do babies whoare receiving this treatment have their eyes covered?
6..For children age 4 and younger, abuse and neglect are theleading causes of death. Pediatric units must have equipment
to serve patients who have multiple system injuries (that is,
brain injuries, respiratory problems, broken bones, and burns).Research, document, and describe the types of equipmentrequired to support these patients. Discuss how these152 Introduction to Biomedical Instrumentation

multisystem injuries in fluence hospital care, equipment
purchase decisions, and hospital spending priorities. Re flect
briefly on the community pro file that is served by a particular
hospital and how the population of children might in fluence
equipment purchasing decisions.
7..Hyperbaric oxygenation is used to increase wound healing,
including burns. Use the Internet to research and documentthe many methods of exposing patients to high concentrationsof oxygen to improve healing. Summarize the therapy methods,
the equipment used, the bene fits to patients, and the type of
patients served.
8..Research and summarize th e interference to medical
telemetry caused by the DTV test in Dallas in 1998. Describe
what happened. Discuss the changes that occurred afterthis problem. De fine and describe WMTS. How will a dedicated
frequency spectrum (WMTS) avoid these types of problems?The intensive care unit 153

11
The operating room
LEARNING OBJECTIVES
1.list and describe the characteristics of surgical lights
2.list and describe the two functions of an anesthesiologist or
CRNA (monitor patient and deliver medications)
3.list and describe the four functions of anesthesia
4.list and describe the staff in an OR
5.list and describe the items that must be worn in the OR
6.list and describe the four types of surgical procedures
7.list and describe the many surgical specialties
8.list and describe the two common methods of equipmentsterilization
9.list and describe the stress related to the operating room
environment
10.list and describe where patients go immediately after surgery
11.list and describe the function of the following pieces of ORequipment: depth-of-anesthesia monitors, operating micro-scopes, robots, smoke evacuators, patient warmers, blood andfluid warmers, operating room tables
12.list and describe laparoscopic surgery and the devicesused in it
155

13.list and describe the functions and parts of an electrosurgical unit
14.define the term LASER and describe some common medical
LASERs
Introduction
The operating room (OR) in a hospital is a unique environment
that contains a great deal of equipment as well as many protocolsand rules that impact a BMET. Many types of surgery are per-formed here. Operating rooms may be located in a hospital, in afree-standing surgery center, or in a doctor’ so ffice. BMETs must
have a solid and accurate understanding of the operating room inorder to perform their job effectively. A typical operating room isshown in Figure 11.1; it bears little resemblance to the operatingrooms depicted in the media.
Figure 11.1. Typical operating room.156 Introduction to Biomedical Instrumentation

PART I –THE ENVIRONMENT
Prior to surgery
Before surgery, patients are often placed in a pre-op area ,a l s o
called the surgery prep. Here, patients are often asked to
remove their clothes and put on a hospital gown, socks, hairnet, and other specialized items. Questions are asked about the
person’ s medical history, allergies, and other information.
Some preliminary testing (blood work and urinalysis, for
example) may be done. A meeting with the anesthesiologist
(the doctor who controls the anesthesia delivered to thepatient, which make the procedure possible) often occurs at this
time.
The operating room
A patient is brought to the operating room by wheelchair orportable bed before being moved onto the operating table. The
operating table is at the center of most operating rooms and may
be surrounded by various other small tables and carts. Thesehold the equipment and tools needed for the operation.Mounted on the ceiling are bright, specialized lights called sur-
gical lights. An example of one type of surgical light is shown in
Figure 11.2. These are sometimes controlled by foot pedals so
they can be positioned during procedures (also called surgical
cases ). The handle that sticks out of the middle of the bank of
lights is usually covered with a plastic hand piece that is sterilizedso the staff can move the light during the case.The operating room 157

Anesthesiology
Theanesthesia and monitoring equipment are kept at the head
of the OR table. This is where the anesthesiologist or Certifi ed
Registered Nurse Anesthetist (CRNA) delivers medications for
anesthesia and monitors the patient during the surgical pro-cedure. Most of the equipment they use is on a cart (sometimescalled a workstation). Draeger is one of the main producers ofanesthesia equipment.
Once the patient is correctly positioned on the table (there are
standard positions used for speci fic surgeries), medications are used
to perform four major functions (not all will be used all the time):
1..Analgesia –pain relief
2..Paralysis (are flexia) –immobilization (blockage of
reflexes like breathing)
3..Amnesia –memory loss of events that take place in the OR
4..Sedation –deep sleep
Figure 11.2. Operating room lights.158 Introduction to Biomedical Instrumentation

Types of anesthetic agents (medicines) include gases like nitrous
oxide, sevo flurane, des flurane, isofl urane, and halothane. Other
drugs (liquid) are also typically given to patients in the intravenous
(IV) lines to accomplish some of the four functions previously
described. Different anesthetic agents have different actions on thebody and are useful in different procedures. Ether gas was acommon anesthetic in the past. It is now banned in the UnitedStates because of its flammability. Older operating rooms may still
contain vestiges of equipment used to prevent explosions.
There are three types of anesthesia:
1..General anesthesia –patients are dependent on a
ventilator in this situation, this is “going to sleep ”
2..Local anesthesia (often uses novocaine)
3..Regional anesthesia –spinal or epidural
Staff in the OR
Nurses: Two types of nurses work in the operating room: cir-
culating nurses and scrub nurses. Circulating nurses prepare the
patient for surgery by setting up the IV, attaching the monitoringdevices, and helping the anesthesiologist. It is the responsibilityof the circulating nurse to prepare the operating room for sur-gery, set up equipment, and help the scrub nurse place theinstruments on the table. During surgery, the circulating nursesometimes passes items to the surgical team and will also be the
one to leave the room if something else is needed or if lab tests
need to be performed. Because this nurse is not part of the sterile
field(the area where the procedure is performed that needs to
remain as germ free as possible), she or he takes precautions notThe operating room 159

to contaminate it. The scrub nurse prepares the sterile field,
surgical supplies, and equipment. During surgery, the scrub
nurse assists the surgeon by passing instruments, suctioning
blood, and maintaining the sterile field. Scrub nurses work
closely with the operating room team, making sure that every-
thing goes smoothly. After surgery, the scrub nurse or technicianwashes the “specials ,”which are instruments that personally
belong to the surgeon. Some scrub nurses work with only speci fic
surgeons and may be employed by them.
CRNAs: Certified Registered Nurse Anesthetists are specialized
nurses who deliver anesthesia. Many BMETs work closely with
the CRNAs in a hospital in relation to the equipment in theoperating rooms.
Surgical technicians : Also known as surgical or operating room
technicians, surgical technicians assist in procedures under the
supervision of surgeons, registered nurses, or other surgicalpersonnel. They usually have about one year of specializedtraining from which they earn a certi ficate.
The sterile environment
The operating room staff wear special out fits called scrubs (a
shirt and pants) supplied by the hospital. These clothes are notsterile, but they have been washed under strict guidelines and are
presumed to be cleaner than an individual ’s“street ”clothes.
(Underclothes and perhaps a T- shirt may be left on, but, for most
situations, all other clothes are removed.) Everyone in the room(including BMETs) wears caps, masks, and booties (shoe covers).Facial hair must be covered using a beard cover or sideburn cover.160 Introduction to Biomedical Instrumentation

Workers who are in the sterile field wear additional gowns
(like a long dress) and rubber gloves. These garments help protect
both the person having surgery and the operating room staff
against infection and disease. Remember, some diseases (like
AIDS) are assumed to be present since a patient cannot beinvoluntarily tested. Always assume that items in the OR have
been contaminated with bodily fluids.
BMETs are not usually in the sterile field.U n l e s st h e r ei s
a particular reason, BMETs must avoid entering the sterile
field, touching it, or compromising it. ( Note: The sterile field
includes sterile staff. BMETs should never break the sterile field
by touching a sterile item or staff member.) BMETs always
remain in the nonsterile field (everywhere else in the room).
Regulations regarding the sterile and nonsterile fields vary from
hospital to hospital and are usually well de fined and commu-
nicated. Ask questions when unsure of protocol. Following theguidelines of the institution is important for patient andpersonal safety.
Types of surgery
The four different types of surgery are:
▶Diagnostic –This surgery can be for a biopsy or to “see”
what an organ or system looks like.
▶Preventative –These procedures may prevent a problem
before it happens.
▶Curative –Patients undergo this type of surgery when a
situation can be corrected with a procedure (removing atumor or repairing a broken bone, for example).
▶Palliative –This surgery will enhance the quality of life and
can be purely cosmetic or restorative.The operating room 161

Surgical specialties: There are many specialties and subspecialties.
For example, a surgeon could operate on pediatric patients with
cardiac issues.
▶Oncology –cancer treatment
▶Orthopedics –bone problems
▶Pediatric –young patients, usually under 18
▶Neurology –issues of the brain and spinal cord
▶Urology –reproductive functions of men, urinary tract in
both men and women (kidney and bladder)
▶Obstetrics –pregnancy and childbirth
▶Gynecology –reproductive system of women
▶Plastic/cosmetic –correction to the form of the human
body; cosmetic surgery relates to enhancement, andreconstructive surgery is used to correct function
▶Cardiac/thoracic –the heart
▶Ophthalmology –the eyes
▶Otolaryngology –related to the ear, nose, and throat
(sometimes called ENTs)
Equipment sterilization
Surgical equipment that is reused must be cleaned and sterilized
between uses. Items that need to be sterilized include surgicalinstruments like clamps as well as tools like electric drills. Thisprocess can be time consuming and detrimental to the electronicscontained inside equipment. Some devices have been carefully
designed to be one-time use (disposable) and therefore are not
sterilized again.
The most common methods used to sterilize equipment and
instruments are162 Introduction to Biomedical Instrumentation

▶Autoclave –uses saturated steam at high pressure to kill
germs (some are dry heat).
▶EtO (ethylene oxide), Sterris is the main manufacturer –uses
a gas (harmful to humans) to destroy germs. It does not use
high heat and pressure like the autoclave and therefore can
be better for some equipment. An example of a sterilizer isshown in Figure 11.3.
Many hospitals designate an area of the hospital in which toprocess equipment for cleaning and sterilization. Often this areais called Central Sterile, Central Stores, or Central Supply and isabbreviated CS. Staff who work in this area use the sterilization
methods described here as well as disinfecting solutions to clean
equipment.
Operating room stress and customer service
The operating room is probably the area of the hospital that isthe most stressful for the staff. Patients undergo procedures that,even when simple, can have life-threatening complications. Cer-tainly, it is possible that patients who undergo surgery thatexposes the heart could have dif ficulties, but even simple pro-
cedures carry risk. As a result, staff depend on the proper andpredictable functioning of all equipment all the time. Whendevices fail to perform as expected, the stress can become visible. Itis understandable. BMETs need to provide customer service to thestaff with an understanding of the concerns and focus on thepatient. Prompt and calm response to a malfunction is critical.
Remember that some issues (procedural problems, for example)
should be dealt with after the surgical case is completed.The operating room 163

Figure 11.3. Sterilizer.164 Introduction to Biomedical Instrumentation

The fast-paced, high-stress environment of the operating
room can cause equipment to fail frequently. Fluids, both from
the patient as well as from the procedures, are a constant
problem for electronic equipment. Equipment can be acciden-
tally dropped and roughly handled simply because of thefocus on the condition of the patient. Also, the cleaning ofequipment after procedures, while essential, adds opportunitiesfor damage.
PACU
After surgery, patients are taken to an area called post-op, the
recovery room, or post-anesthesia care unit (PACU). Here,
careful monitoring takes place as the patients recover fromanesthesia. Nurses and other staff check vital signs, assist withpain relief as the patient wakes up, address surgical site issues
(incision care), and generally provide close supervision. Patients
eventually are sent to a regular patient room, an ICU bed, or home.
PART II –EQUIPMENT IN THE OR
There are many unique types of equipment used in an OR.Recognize that a BMET ’s list does not include surgical instru-
ments (clamps and retractors, for example). Most of these are theresponsibility of the surgery department. In orthopedics, how-ever, there are some electric devices, such as drills, that might fallinto the BMET domain. In addition, many devices found in anoperating room are commonly found elsewhere in the clinicalsetting. Common equipment includes monitors, IV pumps, andThe operating room 165

defibrillators. Some other types of equipment that may be more
specific to the operating room include:
▶Depth-of-anesthesia monitors –Sometimes called BIS
monitors (BIS is a brand name), these devices are able to
quantify (on a scale of 0 –100) the consciousness of the
patient using the EEG. They are discussed in Chapter 9.
▶Anesthesia machines –These devices deliver anesthetic
gases (discussed in Chapter 8). Even though anesthesiamachines are fundamentally ventilators, they have somespecial features. One important function prevents thedelivery of more than one anesthetic gas at a time (often
there are three or four available). An example of an
anesthesia machine is shown in Figure 11.4. You can tellthat this machine can deliver three different gases becausethere are three sets of pressure gauges and three cylinders onthe right-hand side of the device.
▶Operating microscopes –These devices are used to better
visualize the surgical field. They are usually binocular and
are typically mechanical in nature.
▶Robotics –These complex devices hold and move
laparoscopic instruments. An example of robotics is calledthe da Vinci System. Surgeons use computer-controlled
equipment to have finer control of instruments. However,
robotics are not found in many ORs because they are usefulfor only a few specifi c types of surgical cases, require special
training, and are very costly.
▶Smoke evacuators –These devices are used to remove the
material (sometimes called smoke or plume) created byelectrosurgical units and LASERs. These common devices
may also be called plume evacuators.166 Introduction to Biomedical Instrumentation

▶Patient warmers –These devices usually contain warm air
that circulates in plastic “blankets. ”These may also be found
in emergency rooms and other parts of the hospital. (The
Bair Hugger is a common brand.) Similar devices may alsocool patients.
▶Blood and fluid warmers –These devices, which quickly
heat blood to body temperature, often use heated metal
Figure 11.4. Anesthesia machine.The operating room 167

plates or warm water baths. They may also be found in the
emergency room.
▶Operating room tables –Patients lie on special tables that
can be moved up and down and tilt. These tables are oftencontrolled by foot pedals.
▶Operating room lights –These devices need to be very
bright and present white light that will not influence theappearance of the patient (shown in Figure 11.2).
▶Saws and drills –These tools are used to work with bones in
orthopedic surgery. They come in many shapes and sizesand are carefully designed for the hospital environment.
Equipment used in laparoscopic surgery
Since the early 1990s, there has been an increase and improve-ment in the use of minimally invasive surgery. Laparoscopic
procedures involve the use of a video camera and a light source,
which is put into a patient through a small opening. The surgicalinstruments are passed through other holes. The Web site http://www.laparoscopy.com contains a great deal of information aboutthese procedures. This site contains many details that are notimportant to BMETs. The equipment should be the focus of this
information.
Scopes : Scopes, which are essentially video cameras, can be either
rigid or flexible. Rigid scopes are used for joint surgery and are
often called arthroscopes.
▶Scopes almost always use fiber optics for the light conductor
with a xenon lamp as the source.168 Introduction to Biomedical Instrumentation

▶The image is almost always seen through a video camera, but
it can be viewed through an eyepiece at the end of the shaft.
▶Most scopes also have a channel through which fluids,
instruments, and gas can be sent into the patient. Manyprocedures, though, use other incision points to passinstruments into the patient.
Flexible scopes may be called endoscopes, gastroscopes, procto-
scopes, duodenoscopes, bronchoscopes, and cystoscopes .T h e
part of the body on which these are used is re flected in the name.
Because flexible scopes generally enter the body through a natural
opening (mouth, nose, urethra), all of the instruments and fluids
must be passed through the scope. These devices may also be usedoutside of surgical cases to examine areas of the body such as thenose or throat.
Trochars: These pointed devices are used to make the hole in the
skin to penetrate into the body cavity. They may be spring loaded.Insuf flators: These devices, which are used during laparoscopic
procedures, create a gas- filled space within the abdomen in order
to move the internal organs out of the way.
Electrosurgical units (ESUs)
These devices are very common in surgery because they are used
to assist the surgeon with cutting –that is, making an incision
into the tissue (cauterization ) and limiting bleeding (coagulation).
ESUs often have two settings, labeled CUT and COAG . Origin-
ally, these devices were very basic AC-powered sources that pro-duced waveforms in the RF range 300– 3,000 kHz. Today, these
ESUs are very complex, microprocessor-driven devices. AnThe operating room 169

example is shown in Figure 11.5. These devices are sometimes
referred to as “Bovies ”because this is the name of the original
inventor, as well as the first brand of units.
The alternative to the use of an ESU is very time consuming, with
a less-than-optimal outcome. Wi thout an ESU, all incisions would
have to be made with knives, and all bleeding would have to be
stopped with sutures to tie blood vessels closed. ESUs are a
wonderful technology, b ut there can be problems –occasionally
there are unintended burns to both patients and hospital staff.
Electrosurgical units offer complex and varied waveforms
controlled by microprocessors. ESUs operate using one of twoenergy waveforms. Monopolar waveforms use one source of elec-
trical energy. Monopolar devices are often called pencils. A pencil isshown in Figure 11.6. Notice that the pencil has two buttons, onefor
CUT and one for COAG. This energy travels from the pencil
through the patient to the “return electrode ”pad. This disposable
and sticky pad is filled with electrically conductive gel and returns
the energy to the ESU generator. The return electrode is placed on
Figure 11.5. Electrosurgical unit (ESU).170 Introduction to Biomedical Instrumentation

the patient in a location that is away from the surgical field. Good
contact is important because it is likely that the area used will be
covered in sterile drapes and not visible to the staff. Many ESUsmaintain a circuit to check the integrity of the return electrode
pad –called the return electrode monitor or REM. Should the
return electrode become dislodged, the ESU will not work (which
can be frustrating to the surgeon during a case).
The second type of ESU energy waveform is bipolar. This
process passes electrical energy between the two tips of a probe,which looks like tweezers. An example is shown in Figure 11.7. In
this form, the electrical energy is very concentrated. The bipolar form
is very useful when both ends of the tissue are accessible (such as ablood vessel). However, bipolar cannot be used to create an incision.
Technology used in the cutting and coagulation efforts
of surgery have expanded to include the use of LASER light(typically argon) to effect tissue. Also, there are speci fically
designed waveforms that have very speci fic effects on tissue. For
example, Ligasure fuses tissue or vessels without burning.
Figure 11.6. ESU pencil (one button is for CUT and one button is for COAG).The operating room 171

As the electrical energy is passed through the tissue, gaseous
material (plume) is typically generated. It may be removed from
the surgical area by a smoke/plume evacuator.
LASERs
The acronym LASER stands for Light Ampli fication by the
Stimulated Emission of Radiation. This device uses speciallytreated light to alter tissues in a speci fic way. LASERs typically
coagulate or vaporize (cut) tissue.
In general, LASER light waves are:
▶Coherent –All of the light waves are in a single phase.
▶Monochromatic –All of the light waves are of a single color
(frequency).
Figure 11.7. Bipolar electrosurgical tool.172 Introduction to Biomedical Instrumentation

▶Collimated –The light waves are capable of staying together
in a tight beam over long distances.
Some LASERs are capable of producing more than one color and
produce different tissue effects. LASER light can be made fromfour different sources (mediums): solid, liquid, gas, or electronic.
Some common types of medical LASERs are:
▶CO 2(carbon dioxide) –very common surgical LASER for
cutting and coagulation
▶Nd:YAG (neodymium yttrium aluminum garnet)
▶Tunable dye
▶Argon
▶Ruby
Some functions of LASERs include corrective eye surgery, removalof tumors, removal of tattoos, and skin resurfacing.
STUDY QUESTIONS
1..Describe the responsibilities of anesthesiologists. Include
the technologies used by anesthesiologists to support patients.
2..Describe what a BMET would wear to enter an operating room.
3..What are the types of surgical specialties? Create a list of each
type. Flash cards may assist in this effort.
4..Identify and describe some of the customer service qualities
that are important for BMETs in the OR.
5..Identify and describe some of the environmental pressures onequipment that are speci fic to OR equipment.
6..Make a list of common equipment you would find for a typical
case (not laparoscopic or robotic) in an operating room.The operating room 173

7..Identify the type of electrosurgical technique that requires a
return electrode. Sketch the electrical path (from the ESU –
back to the ESU) through the patient.
FOR FURTHER EXPLORATION
1..Use the Internet to research OR patient tables. Document theircharacteristics. Describe the features that make them different
from the beds used in patient care rooms. Identify and describe
some of the types of OR patient tables that are designed forspecific types of surgery.
2..Use the Internet to research the use of irrigation duringsurgical procedures. Discuss how this impacts the surgical field.
There has been a great deal of debate as to whether ORs should
be de fined as wet locations by NFPA (currently, they are not). In
addition, Cesarean sections, which deliver infants, release a
great deal of amniotic fluid. Discuss how this too contributes
to the wetness of the surgical area. Discuss how technology andstaff within this area must be aware of the impact of the fluids.
3..Research and document some standard patient positions with
names such as Sims, Fowlers, prone, supine, lithotomy, and
Trendelenburg.
4..Research and describe the steps required in the EtO (mostcommon) sterilization process for equipment reuse.
5..Research and summarize the characteristics of orthopedicequipment such as drills used in surgery. How do they differ
from the kind of tools found in a hardware store?
6..Robotic surgery is very popular in the media. Research the
components of robotic surgery and summarize them. Describesome advantages and disadvantages of robotic use in surgery.174 Introduction to Biomedical Instrumentation

7..Explosions were a constant threat with the use of ether.
Define and describe ether as an anesthetic gas. Explore and
summarize historical information to find out what precautions
were taken to avoid dangers in operating rooms that used ether.Be sure to discuss such precautions as flooring restrictions and
electrical plug con figurations. If possible, include the testing
required of BMETs to ensure safety in operating rooms thatused ether.
8..List and describe the equipment needed for a laparoscopic
appendectomy. Describe the advantages to the patient of a
laparoscopic appendectomy instead of a traditional procedurewith an abdominal incision.
9..When patient illustrations are viewed at http://www.laparoscopy.com, patients often appear very large and bloated. Why is that?Specifically identify the equipment that causes this condition.
Explain why this in flation is necessary.
10..Valley Lab (a major manufacturer) produces good referencematerials. Use the following site as a useful resource: http://www.valleylab.com/education/poes/index.html (Review thePrinciples of Electrosurgery link on the left). De fine and
describe the following concepts:
▷bipolar and monopolar mode
▷patient return electrode use and placement
▷REM (return electrode monitoring)
▷basic setup and function of the use of an ESU
11..Identify and describe the potential life-threatening medicalcomplications that could compromise patients undergoing
even the most simple and short surgical procedure. ( Hint:
Search the Internet for surgical complications. ) Identify and
describe potential equipment-related hazards for patients
(include hazards from LASERs and ESU devices).The operating room 175

12..Cardiac surgery often involves specialized equipment not described
in this chapter. Examples include bypass machines and pacemakerprogramming devices. Research, identify, and describe these
devices. Identify other devices used in cardiac surgery.
13..Visit this Web site, http://www.streamor.com/orintro/
orintroindex.html, to view streaming video of an OR. TheWeb site contains a great deal of information about the staff inan OR as well as what scrubbing means. Prepare a summary of:
▷people in the OR
▷equipment in the OR
▷scrubbing for the OR
▷sterile techniques176 Introduction to Biomedical Instrumentation

12
Imaging
LEARNING OBJECTIVES
1.describe ultrasound imaging
2.describe basic x-ray imaging
3.describe CT scanners and identify how they differ from basic
x-ray devices
4.describe DICOM and PACS
5.describe and characterize MRI
6.describe and characterize nuclear medicine –both imaging and
treatment
7.describe and characterize PET scans
177

Introduction
The technology involved in imaging the inside of the human body
is tremendous and amazingly broad. There are a vast array of
unique devices, but this chapter will deal with general categories(based on the technique or source of image) of imaging devices.
Ultrasound
Ultrasound uses sound waves to image anatomy and anatomicalfunction. Ultrasound can also be used to detect blood flow,
anatomic movement (heart valves, for example), and, mostcommonly, anatomical structures. It is frequently chosen as animaging modality because it does not use radiation and carries
less risk to the patient. Ultrasound uses high-frequency sound
waves (1 –20 MHz) that are projected into the body. The waves hit
an object, bounce back, and are detected with a piezoelectriccrystal sensor. The distance from the transmitter probe and theanatomical structure can be calculated, and this data is used toproduce an image. Computers can manipulate the transducer
data to present three-dimensional or moving images.
Transducer probes, which contain both the transmitter and
the sensor, come in many shapes and sizes. Some are designed to
enter body cavities such as the esophagus and the vagina for betterimaging quality. Most commonly, probes are placed on top of theskin and transmit into soft tissues. Ultrasound waves are blocked
by air and bone. This can be a problem since air is contained in the
lungs and there are bones surrounding some organs like the brainand heart. A gel is often used to help block any air between theprobe and the skin. This ensures effective transmission of the178 Introduction to Biomedical Instrumentation

waves and unobstructed images. An example of a probe used for a
trans-thoracic (cardiac) ultrasound is shown in Figure 12.1.
Because of the inherent safety of this type of imaging, women
often undergo ultrasound imaging to evaluate the progress ofpregnancy. Many infant abnormalities can be detected early and,in some cases, perinatal treatment can take place. Another com-
mon application of ultrasound is echocardiography. The anatomy
and function of the heart can be examined. The data from thetransducer is paired with ECG information to provide the cardi-ologist a great deal of heart performance information. A portableultrasound machine is shown in Figure 12.2.
X-rays
Radiation comes in many wavelengths, a common one is thex-ray. The x-ray wavelength evolved to become the name of a
Figure 12.1. Trans-thoracic ultrasound probe.Imaging 179

Figure 12.2. Ultrasound machine.

device, a machine that uses this wavelength of radiation. A basic
x-ray machine, used to check on a broken ankle or arm, has along history and serves a useful purpose. X-rays are blocked by
different materials at different levels, including the calcium in
bones and teeth. An image can be created in a fairly basic way.The machine uses a source of x-rays (in a carefully controlledhousing) and a type of film that is altered by x-rays. The patient
(who is a source of x-ray blocking materials such as bone) isplaced in between the source of x-rays and the film. Conse-
quently, the image formed shows exposed film surrounded by a
shadow of the bone of the patient. This type of imaging iscommonly used in dentist of fices and hospitals and can simply
diagnose many diseases and injuries. X-ray imaging can beadapted for more specialized medical uses. For example, mam-
mography is simply a specialized x-ray for the breast. X-rays are
also used in CT devices and fluoroscopy machines.
Computed tomography or computerized axialtomographyThe computed tomography (CT) or computerized axial tomog-r a p h y( C A T )m a c h i n ei ss h a p e dl i k eal a r g ed o n u t .A st h ep a t i e n tl i e s
in the center of the CT unit, an x-ray tube circles the patient,
sending x-rays into the patient at many locations. Multipledetectors pick up the radiation. A computer combines the manyindividual x-ray images into cross-sectional pictures, or “slices” of
the body. The absorption characteristics of the radiated tissues(especially with the use of contra st agents injected into the body)
and the intensity of the x-ray beam produce images showinginternal structures such as blood clots, skull fractures, tumors, andinfections. The ability to image soft tissues (compared with thebasic x-ray system) was a tremendous advancement in medicalImaging 181

imaging. Basic CT images are typically cross-sectional views of the
body (similar to a slice of bread as if the loaf were the human body).As CT technology has integrated more techniques, the imagesgenerated from the many sources and detectors can be manipulatedto create rotatable, three-dimens ional images or three-dimensional
plastic models. A common CT scanner is shown in Figure 12.3.
Fluoroscopy
This real-time x-ray imaging system produces images on a videocamera (either analog or digital). Essentially, the x-ray images are
Figure 12.3. CT scanner.182 Introduction to Biomedical Instrumentation

able to continuously change as the patient (or something inside
the patient) moves. Fluoroscopy, for example, can track themovement of a chemical through the digestive tract as a patient
swallows. Fluoroscopy got its name from the use of fluorescent
screens that previously displayed the moving image before the
use of cameras. Angiography, a speci fic use of fluoroscopy, allows
physicians the ability to look at blood flow through the blood
vessels using fluoroscopy. Cardiac catheterization and angio-
plasty use the real-time images to view coronary blood flow and
treat blockages. C-arm devices are fluoroscopic x-ray machines,
which can be portable or fixed. Many times these are digital
devices (producing a digital image rather than using film) and are
useful in many applications including during surgical cases. A c-arm is shown in Figure 12.4.
Common applications of x-ray imaging
Cardiac catheterization: In this procedure, a doctor guides a
catheter through an artery or vein in the arm or leg, into theheart, and then into the coronary arteries in the heart. Thecatheter is visible to x-rays to guide the insertion. Using spe-cialized chemicals, the procedure can measure blood pressure
and how much oxygen is in the blood and can provide other
information about the pumping ability of the heart muscle orfor treatment. The process is guided using moving x-ray images.When a catheter is used to inject dye into the coronary arteries,this is termed coronary angiography or coronary arteriography.If a catheter has a balloon on the tip, the procedure is known as
percutaneous transluminal coronary angioplasty (PTCA).
Angioplasty: PTCA is a procedure used to dilate (widen) nar-
rowed arteries. Using the guidance of x-rays and a fluoroscopicImaging 183

camera, a doctor inserts a catheter with a defl ated balloon at its
tip into the narrowed part of the artery. Then the balloon is
inflated, compressing the plaque and enlarging the inner diam-
eter of the blood vessel so blood can flow more easily. Then the
balloon is de flated and the catheter removed. LASERs are often
used to assist in the widening of arteries, and stents are fre-quently placed in the artery during this procedure.
Figure 12.4. C-arm portable fluoroscopy unit.184 Introduction to Biomedical Instrumentation

Contrast medium , or, more simply, “contrast ”may be added to
specific areas of a patient (soft tissue structures such as blood
vessels or parts of the urinary or digestive system) to enhance the
x-ray images. The solution changes the way some tissues and
organs appear to x-rays. Sometimes contrast agents may be called“dye ”but contrast medium is not a colored dye. To enter the
body, contrast may be swallowed or injected (through a catheter),inhaled, or inserted into a body cavity.
Magnetic resonance imaging
Magnetic resonance imaging (MRI) uses magnets and radio waves(not radiation). First, the subject is placed inside a tremendouslyhigh-powered electromagnet (0.2 –3 tesla (T), although this is
constantly changing as research and design expand MRI applica-tions). This causes the hydrogen atoms inside the human to alignwith the north and south poles of the magnet. Then pulses ofradio waves (at a wavelength designed to excite just hydrogen) aredelivered to the patient. This causes the hydrogen atoms to spin.As they come to realign with the magnets, they give off radio
waves. The radio waves can be picked up by a detector and the
information about the hydrogen atoms can be processed bycomputers. Molecules such as glucose are made up of hydrogenatoms. The processing of this data provides information abouthow organs use the glucose, for example. Uniquely, MRI allowsimages of not just the liver but how the liver is functioning.
Fundamentally, MRI images the chemistry of the body. This is very
different from other imaging devices. Normal and abnormal tis-sues of the same organ appear different to this imaging device. Inaddition, MRI imaging is able to see some parts of the body thatImaging 185

Figure 12.5. GE MRI machine. (Photo courtesy of GE Healthcare.)
are not clearly visible to CT scans. An example of an MRI device is
shown in Figure 12.5.
Safety and MRI
Safety must be a top priority when in the presence of an MRImachine because of the extreme power of the magnet used. Thereare interesting precautions that must be taken both in the roomthat houses the MRI as well as for the patients. No metallic objects
can go near the magnet. Screwdrivers can be ripped from the pocket
of a BMET if the magnet is activated. Patients cannot have pace-makers or many kinds of implants (although some embedded inbone may be allowed), and even some metallic inks used in tattooscan be a problem. In addition, patients often need to be monitored186 Introduction to Biomedical Instrumentation

and connected to ventilators and IV pumps while an MRI is per-
formed. Devices must be carefully constructed to shield the metalliccomponents from the powerful magnet and radio waves.
Nuclear medicine
Nuclear medicine uses very small am ounts of radioactive chemicals
to view (and treat) the human body. The use of these materials canbe helpful to image parts of the body (check for tumors, forexample) or to target known areas of disease. Gamma radiation (aspecific wavelength radiation) is used, for example, to scan the
bones. The patient is injected with a very speci ficc h e m i c a l ,w h i c hi s
attracted to the bone and emits radiation. A specialized gamma
camera detects the radiation emitted from the patient. The radio-active chemicals are excreted from the body quickly.
Positron emission tomography
PET is an imaging modality that is able to image organ and tissuefunction with great clarity, and PET scans are able to image tissue
metabolism. A compound, usually sugar, is specially altered to
release positrons (an isotope). This special sugar (FDG) isinjected into the patient. The sugar is transported around thepatient ’s body. The isotope reacts with sugar inside the patient to
produce two gamma rays 180 degrees apart. Inside the scanner, aring of detectors look for the gamma rays and can determine the
location of this special compound in the body. Computers can
correlate all the emission data to map tissues in the body. PETscans have relatively common use in cancer diagnosis becausecancer cells use sugar in high quantities. Currently, PET scans arecombined with CT scanners to produce an anatomical image inImaging 187

combination with the sugar metabolism information. An image
is shown in Figure 12.6.
The isotope is produced using a cyclotron and has a half-life
(amount of time during which half of its radioactivity isdiminished) that limits the distance that the isotope can betransported (essentially restricted to the distance between thescanner and the cyclotron). Commonly used FDG has a half-lifeof about 2 hours, so a careful transportation network is in place
to deliver the compound to the scanner site at the right time.
Other compounds can be used for speci fic applications like
cardiac studies and bone examinations, but these compounds,such as carbon and nitrogen, have such short half-lives that thepracticality of the scans is currently a challenge.
Figure 12.6. PET scan image.188 Introduction to Biomedical Instrumentation

Picture archiving and communication systems
The software and technical speci fications used to store digital
images and, more importantly, access the images on a variety of
devices is vital to the effective use of digital images. Tradition-ally, images were saved on plastic film. A shift in “film”storage
is occurring as images are being c reated in digital form. These
images can then be networked, emailed, and transmitted tomany locations without the plastic sheet being carried from one
place to another. This storage is called PACS, which stands for
picture archiving and communication systems. There is a vital
interrelationship between devices, image access, medical devicemanufacturers, and network computer technology.
DICOM
Digital imaging and computing in medicine (DICOM) is the
standard (the rules) that allows connectivity between the devices,
which acquire the image, and the computers, networks, printers,and servers, which share them. This is the agreed-upon file for-
mat and communication protocols that enables all equipment towork together.
STUDY QUESTIONS
1..Name the two types of imaging modalities most commonly
used to observe organ motion.
2..Identify the main differences between a traditional x-ray deviceand a CT scanner.
3..Define a contrast agent and describe how they are used to
enhance images.Imaging 189

4..A small permanent magnet (such as a decorative magnet) has
the strength of about 0.01 T. Compare this to the magnet usedin MRI devices.
5..Describe some of the practical safety concerns required forwork in MRI rooms.
6..Identify which devices can image organ function.
7..List and describe imaging modalities that use radiation.
FOR FURTHER EXPLORATION
1..Research, list, and describe five measurements taken during a
fetal ultrasound procedure that can indicate abnormalities. Forexample, the distance between the eyes can indicate Downsyndrome. Explore and document what conditions can be
detected during fetal ultrasound.
2..Research, defi ne, and describe ejection fraction and
cardiac output, two numerical values that can be
determined from echocardiography. Identify normal values.Describe abnormal values and t he disease conditions they
may indicate.
3..Real-time videos taken using echocardiography are vital to thecardiologist. Visit http://www.echobasics.de to view real-timevideos of various parts of the heart. Select the section labeled“transthoracic examination. ”Research and defi ne a
transthoracic ultrasound. Describe how the test isperformed. When exploring the Web site, observe the valves
opening and closing.
4..Basic x-ray machines use a Bucky to guide the x-rays. Research,
define, and describe this device. Document its function within
an x-ray machine.190 Introduction to Biomedical Instrumentation

5..Research, document, and explain at least five types of diseases
and conditions that can be detected simply with a basic x-ray
machine. Include both injuries and diseases.
6..Explore the Web site http://www.ptca.org/devices2.html, whichcontains interesting photos of fluoroscopy imaging equipment.
Identify and document the overall purpose of the proceduredescribed. De fine and describe “balloon ”and “stent ”as
described on this Web site.
7..http://www.sprawls.org is an online textbook about medical
imaging. The text is called Physics and Technology of Medical
Imaging. Click on Physical Principles of Medical Imaging to view the
Table of Contents. In the first module, General Medical Imaging
Topics , read the Medical Image Characteristics and Quality Factors
section. De fine image quality. Identify the five image quality
characteristics and de fine and describe each of them.
8..Research, de fine, and describe the ratings that are used on
equipment for use in the MRI room –MRI safe vs.MRI
compatible. How do the ratings differ?
9..Physical size of a patient is a problem for some imaging devices
that must encircle the patient. CT scans and, more commonly,MRI machines do have a limitation in the opening size through
which a patient must fit. Claustrophobia can also be an issue.
Research, document, and describe both physical size
limitations and claustrophobia. Describe the impact of thesesituations on patient care.
10..CT and MRI machines are very expensive. Document anddescribe how the community surrounding a hospital might
impact the number and type of devices of this cost a hospital
can purchase. Research local hospitals to determine how manyof these devices they own, and describe how these statisticsmight vary from rural to urban areas.Imaging 191

11..The journal Medical Imaging is available on the Internet at
http://www.medicalimagingmag.com/. Visit this Web site and
summarize an interesting article.
12..Research the amount of radiation exposure (measured inSieverts) typical for a chest x-ray, a CT scan of the chest, and adose of radioactive material such as PDG during a PET.Compare the dosages and discuss the impact of radiationexposure to patients for different imaging modalities.192 Introduction to Biomedical Instrumentation

13
Clinical laboratory equipment
LEARNING OBJECTIVES
1.describe and characterize the purpose of the clinical laboratory
2.describe Coulter ’s discovery
3.defineflow cytometry and describe why it is useful
4.describe and de fine a fluorochrome and identify why it is useful
5.describe potentiometry
6.define an ion selective electrode and describe its applications
7.define spectrophotometry and describe the application of this
technique
8.define osmolality and describe the application of this technique
9.define an osmometer and identify its basic principle
10.describe electrophoresis
11.describe the principles of operation of a centrifuge
12.identify and describe other types of laboratory equipment
13.describe point-of-care testing
193

Introduction
The clinical laboratory is vital to a hospital ’s ability to treat
patients. Bodily fluids from patients are analyzed for their
chemical makeup and evidence of disease. Many therapeutic and
treatment decisions are made based on the results of thisimportant analysis. Almost all testing is automated and mostdevices perform many tasks. BMET support is vital to the clinicallaboratory, as it is a very equipment-intensive department. The
high level of complex equipment does require some hospitals to
obtain service contracts for the support of clinical laboratoryequipment.
Some of the fluids from patients that are commonly analyzed
include blood, urine, and cerebral spinal fluid. A tremendous
number of tests are performed. This chapter focuses on the
principles that form the foundation for the complex equipment.
Most devices use multiple reagents, bar codes, robotics, andcomputers to perform the sample preparation and multiple tests.
In addition to automated fluid analysis, many laboratory
tests evaluate tissue and fluid samples for evidence of
abnormalities. Many of these tests are not automated and
require the expertise of a pathologist or clinical laboratory
technician.
It is worth noting that the terms “medical technology ”and
“clinical technology ”may be seen interchangeably, although
medical technology is an older label.
Clinical laboratories have their own speci fic regulations and
organizations that offer guidelines and best practices. Theseinclude the American Association of Blood Banks (AABB), Collegeof American Pathologists, and Clinical Laboratory ImprovementAmendments (CLIA). CLIA are federal requirements.194 Introduction to Biomedical Instrumentation

Blood analysis
Many tests are performed on blood. A common test is blood cell
count. The automation of this test was vital to improvement in
analysis speed. W. H. Coulter created an automated method of
particle counting using electrical impedance. As the blood cellspass between electrodes, the impedance increases in pulses. Thesepulses can be counted to determine the amount of cells (particles)in a sample. Since red blood cells and platelets have different sizes,
the pulses vary in size. This allows for very speci fic results.
Blood sample analyzers combine the Coulter technique with
other technologies to provide additional information and/or
faster speed. For example, to determine the amounts of each ofthefive different white blood cell types, flow cytometry and radio
frequency signals are used.
Flow cytometry uses laser beams and photodetectors to measure
the light that passes through cells as well as the light that is
reflected. Fluorescent dyes are commonly used to assist in the
specific cell analysis. Fluorochromes are chemicals used to
identify antigens or antibodies because they are able to absorb
and reemit light. Flow cytometry assists with the identi fication
and sorting of different types of cells in a moving liquid.
Another important quality of blood is the dissolved blood
gases (carbon dioxide and oxygen) and the pH of the blood (nor-
mal blood pH is 7.35 –7.45). Potentiometry is a technique that uses
electrodes to detect the quantity of these substances in a sample bymeasuring the voltage between the electrodes. This has become avery useful technique as ion selective electrodes (ISEs) have been
created. These electrodes are carefully designed to measure theClinical laboratory equipment 195

quantity of speci fic chemicals including glucose, potassium,
fluoride, lead, mercury, and calcium. This technique only requires
very small samples, on the order of microliters. Scienti fice x p e r i –
mentation that creates new ISEs is ongoing and expands the
substances that can be evaluated using this technique.
The use of light in laboratory tests: A majority of clinical lab
measurements use some type of photometry, which simply
means light measurements. Photometry plays an important role
in some of the techniques described earlier. Spectrophotometry
is a technique that exposes a fluid sample to a light beam and
measures the amount of light transmitted through the solution.
Urine tests
Osmolality is the measurement of the concentration (amount) of
particles in solution. The “solution ”is the urine sample. The
“particles ”to be measured are elements such as electrolytes
(sodium, potassium, calcium), glucose, drugs, and antibiotics.
The instrument used to do this is an osmometer. The science of
measuring osmolality is called osmometry .
Osmosis is the process of moving water across a semiperme-
able membrane (the cell wall) until there is an equal concentration
offluid on both sides of the membrane. This is an essential process
for moving nutrients, drugs, and antibiotics into a cell as well asallowing waste materials to pass out from the interior of the cell.
The osmometer is a laboratory device that measures the
osmolality of a solution. Virtually all osmometers in clinicallaboratories determine osmolality by measuring freezing pointdepression, which is a chemical property that is proportional to196 Introduction to Biomedical Instrumentation

the amount of compound in the sample (this principle states
that the freezing point of a liquid is lowered in proportion to theamount of chemical present).
The patient ’s specimen is poured into an analysis vial and a
thermistor probe is used to record temperatures of the sample.Then the sample is cooled and warmed several times duringwhich temperatures are recorded. This data is used in the elec-tronic calculation of the osmolality of the patient ’s specimen.
This data can be compared to known concentrations of com-
pounds to determine the make-up of the particular sample.
Electrophoresis
This technique is used to separate large molecules such as pro-
teins. Applying electrical charge causes molecules to separatebased on weight. Placing the sample in a gel can lock moleculesin place after they are moved by the electrical field. Stains may
also be used to assist in the visibility of molecules in the gel.Samples that contain DNA strands can be “decoded” to assist in
genetic identi fication. DNA pattern matching can be used to
determine tissue sample matches (in forensic investigations) andidentify familial relationships. The resulting patterns in the gelare often shown as visible representation of DNA patterns. Bands
are displayed in Figure 13.1.
Centrifuges
Many automated devices have centrifuges built into them;
nevertheless, stand-alone centrifuges are often found within theclinical lab and in many other locations throughout the hospital.Clinical laboratory equipment 197

Many medical facilities like doctors ’offices have centrifuges as
well. A centrifuge is a device that spins samples to separate the
particles from the solution according to their size, shape, anddensity. Centrifugal force separates the particles.
A centrifuge is basically an electric motor used for spinning
samples of fluid for further analysis. It often contains test-tube-
shaped wells for holding specimens. A typical centrifuge is shown
in Figure 13.2.
A centrifuge spins because of the principles that guide motor
action:
▶Current flows through the field coils (also called stator)
▶Which generates a stationary magnetic field
▶Which generates a magnetic field on the armature (also
called a rotor)
▶Current flows from the brushes onto the armature
commutator
Figure 13.1. DNA electrophoresis gel.198 Introduction to Biomedical Instrumentation

Figure 13.2. Centrifuge.Clinical laboratory equipment 199

▶Current flows through one of the armature coils, which
generates a magnetic field, which is 90 degrees out of phase
with the stationary field
▶Magnetic force tries to align the armature coil
▶As soon as the armature coil starts to move, contact with the
brushes is broken and there is no longer a magnetic field in
the armature coil
▶Meanwhile this process is repeating with another armaturesince it is now in contact with the brushes and that
armature is attracted to the stationary field
As the process of creating an electromagnet and movement(which destroys that electromagnet) is repeated, the armature
continues to rotate.
Speed can be controlled by varying the voltage sent to the field
coils and armature that adjusts the strength of the magnetic field.
Spin is dependent on a balance of samples placed inside the device
(one sample opposite to the other).
Very commonly, the brushes suffer mechanical wear and
must be replaced.
When working on centrifuges, recognize that there is an inher-
ent risk from contamination with bodily fluids that have spilled
or splashed when sample holders are not correctly sealed or break.
Other clinical laboratory equipment
Microscopes: These magni fication devices are often more com-
plicated than the typical light microscope many students haveused during their education. Laboratory microscopes may contain
a digital camera or computer interface.200 Introduction to Biomedical Instrumentation

Microtomes: These specialized tissue slicers “section ”(slice)
samples into very thin pieces for better viewing under a micro-
scope or for further testing. Some of these instruments are
mechanical, but others can be very complex.
Tissue stainers: In an effort to streamline laboratory tests,
automated tissue stainers not only apply stain to samples in
uniform amounts but also agitate the samples, heat them, orperform other actions.
Laboratory-grade refrigerators: Many samples (and blood in the
blood bank) must be kept at precise temperatures to ensure
accuracy and safety. Laboratory refrigerators are able to do this.They operate under the same principles as a household refriger-ator, simply with better temperature monitoring and control.
Refrigerators often have built-in alarms to notify personnel of
errant temperatures.
Point-of-care testing
To streamline patient care and speed up the time between samplecollection and treatment decisions, some common tests can beperformed at the patient bedside. Specialized devices or modulesare often integrated into patient monitors and can perform awide variety of tests. Blood gases, electrolytes, and hemoglobin,for example, can all be tested at the patient bedside. The dramatic
change in the time needed to obtain test results has greatly
enhanced patient care. Figure 13.3 shows a Philips monitor witha rack below that supports modules. Many of the modules arespecific for a type of bedside laboratory test.Clinical laboratory equipment 201

Figure 13.3. Philips IntelliVue Patient Care Monitor with modules for point-of-care
testing. (Photo courtesy of Philips Healthcare.)202 Introduction to Biomedical Instrumentation

STUDY QUESTIONS
1..Describe the role of blood work and urine analysis in patient
care. What are clinicians looking for? What types of informationdo they receive?
2..Describe the role of electrical measurements in automated
blood tests.
3..Identify some commonly performed lab tests on blood.
4..Describe the type of information that is used to determine
heredity (paternity, for example).
5..Identify the parts of a centrifuge. Describe their function.
6..Describe some of the specifi c precautions that must be taken by
BMETs who work on centrifuges in order to prevent disease trans-mission. Include information about PPE from previous chapters.
FOR FUTURE EXPLORATION
1..Search the Internet to research the types of ion selective
electrodes currently available. Document these types andidentify their purpose. How have these innovations improvedthe speed and availability of a wide variety of patient tests?
2..Search the Internet to research, de fine, and describe a
nephelometer. Identify the tests for which this device is used.
3..Research, de fine, and describe turbidimetry. How is this
technique important in the processing of patient samples?
4..Research, define, and describe argose gel. Identify anddescribe its applications.
5..Research, de fine, and describe polymerase chain
reaction (PCR). Describe how PCR is useful in DNAidenti fication.Clinical laboratory equipment 203

6..A common patient care monitor with point-of-care sample
analysis is the Philips IntelliVue. Examine the productdescriptions at http://www.medical.philips.com. Research,
define, and describe laboratory tests the IntelliVue can
perform at the bedside.
7..Barcoding technology is often used to process patient
samples in the clinical laboratory. Identify and describe themethod that is used to “read ”barcodes. Identify and
describe some common barcode formats.204 Introduction to Biomedical Instrumentation

14
Intravenous pumps and other pumps
LEARNING OBJECTIVES
1.identify and describe the function and purpose of an
intravenous pump
2.identify and describe the function and purpose of a syringepump
3.identify and describe the function and purpose of PCA devices
4.identify and describe the function and purpose of feedingpumps
205

Introduction
The use of technology to push fluids into a patient has evolved
and expanded over time. Bottles of fluids used gravity flow to
“drip ”fluids into a patient. As technology expanded into health
care, the bottles were replaced with plastic bags and gravity was
no longer medically adequate. Electromechnical pumps are morereliable and provide constant monitoring of fluid delivery. In
addition, the flexibility of some pumps has improved medication
dosing and caloric delivery. Hospitals have come to depend onthe use of technology to deliver fluids and medications to
patients.
Infusion pumps
One of the most common pieces of equipment in the hospital,the infusion pump (also called intravenous pump, IVAC, and IVpump) delivers medication, blood, or fluid into the patient over a
specific period of time at a particular rate. The name used may
reflect brand names from the past, including IVAC. Many
patients will be connected to several pumps delivering fluids to
the patient through a vein (hence, the term “intravenous ”). The
pump ensures an accurate rate and, therefore, an exact dose. Inaddition, should there be a problem with the fluid delivery, an
occlusion perhaps, or if the correct fluid amount has been
delivered, an alarm will sound to alert staff. The electronic
monitoring allows delivery of IV fluids with far less human
intervention.
IV bags, filled with fluid, are connected through tubing to the
pump, and then through the pump to the veins of the patient.206 Introduction to Biomedical Instrumentation

Settings on the device include delivery/ flow rate as well as alarms
to indicate blockages or empty fluid bags.
There are different techniques employed to pump in the
fluid. One of the most common is a peristaltic pump . Rollers (in
most cases) squeeze the tubing to push in the fluid. Traditional
tubing from the fluid- filled bag to the patient is used.
Another method requires some additional disposable cas-
settes that hold the liquid for a piston to push the liquid. This
Figure 14.1. Alaris pump.Intravenous pumps and other pumps 207

Figure 14.2. Syringe pump.208 Introduction to Biomedical Instrumentation

requires that the IV tubing be specifically chosen to work with the
type of pump the hospital owns.
In Figure 14.1, a pump that has some memory for dosages
of medications is shown. The blue screen in the center is the“brain, ”and the vertical unit on the left provides the pumping
action to deliver fluids into the patient.
As a BMET, you will have to deal with many different
manufacturers and models of pumps in your career. Many BMETsbegin their internships working on these devices, which often take
a great deal of abuse and are commonly in the BMET shop.
Syringe pumps
Syringe pumps deliver medication from a syringe by using a
piston to drive the back of a standard syringe. This device is
usually used for very small amounts of medication delivered veryaccurately. As with IV pumps, the medication is usually deliveredto patients through their veins. Dosing instructions (time andamount) are programmed by the clinical staff. There are manymanufacturers and models, but a typical syringe pump is shown
in Figure 14.2.
PCA pumps
Patient-controlled analgesia (PCA) pumps deliver pain relief to
the patient through an intravenous line, typically from a sealed
cartridge, when a patient requests relief. Usually, the patient isgiven a push button to trigger the delivery of medication.Obviously, the pump limits the maximum amount of medicationIntravenous pumps and other pumps 209

that a patient can receive. In addition, the pump can be pro-
grammed to limit the dose frequency. Generally, controls arelocated behind a panel inaccessible to the patient. Pumps with
patient control offer better pain management and more accurate
medication dosing.
Feeding pumps
Feeding pumps are used to feed patients suffering from chronic
conditions who must be fed using a feeding tube. The patient isoften connected to the feeding pump via a naso-gastric tube(discussed in Chapter 10). Because feeding liquids may be thick,gravity alone may not reliably deliver calories into the stomach.Feeding tubes are often connected to pumps that deliver enteral
nutrition. This is especially true for premature infants who do
not have a fully developed sucking re flex. A popular brand is the
Kangaroo Pump.
Implantable insulin pumps
Diabetes is a very common condition in today ’s population. To
deliver insulin, some patients use implantable insulin pumps .
The name is a bit confusing because the pump is not implantedinto the patient. However, the device does more closely match thepancreas by delivering insulin in a way that is much more con-
tinuous compared to injections that are typically self-delivered
several times throughout the day. The patient has a port throughthe skin and a catheter is connected to a device that deliversinsulin slowly. Some devices have the ability to monitor the210 Introduction to Biomedical Instrumentation

patient ’s blood glucose levels and adjust insulin amounts as
necessary.
STUDY QUESTIONS
1..Identify and describe the bene fits of the use of technology to
deliver medications and fluids.
2..Summarize the two methods of function of IV pumps.
3..Identify and describe the bene fits of the use of PCA.
4..Describe what part of an implantable insulin pump is actually
implanted.
FOR FURTHER EXPLORATION
1..Identify and describe why intravenous pumps are the mostnumerous device in hospitals. Why do many patients havemultiple pumps? How does this impact BMETs who areresponsible for technology support?
2..Intravenous pumps that use software to store medication
types and dosing guidelines are becoming more common.
Describe how these IV pumps can improve patient safety. Howcan these features dramatically increase the workload ofBMETs?
3..Identify and describe some common types of fluids delivered by
IV pumps.
4..IV pumps often stay with patients throughout their hospitalstays. For example, a patient may move from an ICU to aregular patient floor. Describe how this may complicate
equipment tracking. Research, de fine, and describe some assetIntravenous pumps and other pumps 211

management techniques that can be employed to improve IV
pump tracking.
5..“Smart ”IV pumps were a big media event when introduced.
They were seen as a signi ficant way to decrease medication
errors (one of the biggest problems in hospitals). However,there have been several large recalls with this type ofpump. Explore the Internet for media announcements fromthe early 2000s that hail patient safety improvements. Researchand document recalls from the FDA on Alaris pumps. Do the
benefits seem to outweigh the risks?212 Introduction to Biomedical Instrumentation

15
Miscellaneous devices and topics
LEARNING OBJECTIVES
1.describe the role of BMETs in play therapy
2.define and describe fetal monitoring
3.define and describe nurse call systems
4.define and describe infant tracking systems
5.describe the role of BMETs in rehabilitation efforts
6.describe the role of BMETs in long-term patient care
213

Introduction
Many facets of the hospital culture engage technology as part of
patient care, but they do not fit neatly into the traditional cat-
egories discussed so far. Children use technology (game consoles,
for example) in play therapy. Women in labor are monitored usingspecific equipment. In addition, therapists and specialists, such as
those involved in physical therapy and occupational therapy, alsouse technology. This chapter brie fly examines patients who have
long-term support needs.
Play therapy
Children ’s toys have increased in technological complexity over
time. The role of play in a patient ’s recovery is well documented,
and BMETs support this endeavor. BMETs ensure the devices aresafe to use in the clinical setting, are secure from theft, can be
cleaned appropriately, and are repaired when needed. In addition,
some devices need adaptation to suit the needs of a particularpatient. BMETs employed in children ’s hospitals face these
challenges, which may call for creativity and sensitivity.
Fetal monitoring
Fetal monitors usually track uterine contractions and fetal heartrate simultaneously, often printing the information on long
strips of paper. The medical team uses the two pieces of infor-
mation together to evaluate fetal health and labor progress. Afetal monitor is shown in Figure 15.1. Chapter 5 describes fetalheart monitoring that occurs during labor. This monitoring canuse indirect measurements (often using Doppler technology) or214 Introduction to Biomedical Instrumentation

direct, electrical measurements by the use of a scalp electrode,
which connects to the unborn fetus. Doppler ECG monitoringuses a transducer placed on the woman ’s abdomen, usually held
in place by an elastic band. Direct monitoring uses the scalp
electrode and a reference electrode on the mother ’s skin. This
monitoring method requires that the fetus be in a head-down
presentation for delivery. In addition, the amniotic membranesthat surround the fetus must not be intact.
Monitors used in labor can also measure the strength and
duration of contractions. A pressure sensor (strain gauge) is
placed on the mother ’s abdomen. The tightening movements of
the abdominal muscles with each contraction are detected with
the strain gauge. A medical term for contractions is “toco, ”and
these transducers are sometimes called “toco” transducers.
Some fetal monitors use telemetry, which can transmit the
physiological signals through the air wirelessly. This is very valu-
able for patients who may be encouraged to walk during labor. In
addition, some monitors have transducers that are immersible forwater births.
Figure 15.1. Fetal monitor. (Photo courtesy of GE Healthcare.)Miscellaneous devices and topics 215

Fetal monitors are also used for tests on pregnant women,
such as non-stress tests and stress tests. The results of these tests
can provide the medical team with information about the fetal
development and fetal stress. In non-stress tests, the heart rate of
the baby is examined when fetal movement is detected. It isconsidered normal if heart rates increase after movement.Patients are typically provided a push button to record when amovement is felt so that the medical team can evaluate the fetalheart rate. Stress tests involve the comparison of heart rate to
uterine contractions.
Using fetal ECG monitoring and contraction data together,
medical staff can make evaluations of the fetus and its condition
during labor. The collection of this data during labor can beprinted on paper as well as electronically stored and networked.Medical staff located elsewhere in the hospital or at another
location can have access to the electronic records to do “trend ”
analysis. These medical assessments compare the baby ’s heart rate
with the pattern of contractions over time to assess the condition
of both mother and baby. The ability to network data fromlaboring patients is a common hospital request.
There is a less-common method that can measure contraction
strength directly with an intrauterine pressure (IUP) transducer.This is placed inside the uterus.
Nurse call systems
The technology that assists patients calling for assistance is oftentermed “nurse call ”or one word “nursecall. ”What began as a
button that, when pushed by a patient, turned on a light in thehallway, has evolved to include complex wireless paging systems216 Introduction to Biomedical Instrumentation

linked to cell phones and pagers carried by medical staff. The
devices are used at virtually every patient care bed and thereforemany institutions employ one person (or a team) to focus only
on this technology. Fundamentally, a patient in a bed is provided
with a device that has one or more buttons that can be used tosummon assistance, communicate with the unit front desk, andalert staff when there is a problem.
Infant Tracking
Infant tracking systems are used by hospitals to reduce the incidence
of newborn abductions from the clinical setting. Tags worn by the
baby, and in some models, the mother as well, vary in sophisticationbut, in general, can track the baby ’s location and sound alarms if the
infant is removed from a designated area. Radio frequency identi-fication devices (RFID) are often used to tag the infants. Antennas
and portals are used to de fine the permitted areas and can trigger
alarms when necessary. These systems can also be used to avoidinfant switching, where a baby is sent home with the wrong parents.Generally, the tags sound an alarm if removed from the baby.
Rehabilitation
There are many staff involved in the treatments necessary to helppatients regain a level of activity similar to that prior to illness orinjury.
Occupational Therapist (OT): These staff members work to help
patients regain or re fine life skills such as tooth brushing or usingMiscellaneous devices and topics 217

an oven. Some people assume that OTs focus on employment
skills. While this is possible, it is not the most common clinicalapplication. BMETs are often asked to assist OTs to adapt every-
day devices to make them safe for the hospital setting (adding a
ground connection, for example) or appropriate for the needs of aparticular patient. Some of the most interesting equipmentrequests BMETs may receive can come from OTs.
Physical Therapists (PT): These staff members assist patients
with regaining or re fining physical skills such as walking, stand-
ing, and movement in general. Many of their devices are purely
mechanical in design. There are some devices used by PTs that canmeasure range of motion, some motorized exercise equipment,and ultrasound devices, which can soothe soft tissue injuries.
Speech/Audiology
Those involved in the evaluation of hearing use technology. Tonegenerators present audible information at speci fic frequencies
and amplitudes and in variable patterns. In addition to commontone generators, the integration of lights and toys for youngchildren is typical. For children who are too young to followinstructions, the combination of lights, sounds, and mechanical
toys that move (the technician controls the on/off action) allows
the evaluation of hearing.
Long-term care
Patients who have injuries or illness may be dependent ontechnology to support their organ functions. Some examples of218 Introduction to Biomedical Instrumentation

long-term care support include ventilators, feeding pumps,
pacemakers, and renal dialysis machines.
Renal dialysis machines replace the function of the kidneys
by pumping blood through filters that remove the impurities
that would normally be removed by the kidneys. Dialysismachines involve a great deal of mechanical devices and fluids
that might seem more like plumbing. Technicians who work ondialysis equipment must receive speci fic training to ensure the
work meets specifi c standards and ensures patient safety.
Prosthetics can be simple or complex, but they essentially replace
the function of a body part. Examples include arti ficial limbs and
Cochlear implants and could include arti ficial joints. While gener-
ally outside the scope of a BMET ’s responsibility, some technicians
are deeply involved in the creation and support of these devices.
Terminally ill patients
Every human dies. How this happens and what role technologywill play or not play becomes an ethical issue. Because there areseveral devices that can sustain life, “pulling the plug ”is not a
figure of speech. It is, however, a medical and ethical decisionbased on a number of factors, which have been identi fied as:
▶Life-sustaining treatment simply delays death.
▶Degree of physical or mental impairment is or will be
s og r e a tt h a ti ti su n r e a s o n a b l et oe x p e c tt h ep a t i e n tt o
bear it.
▶A particular treatment may be withdrawn or refused withoutregard to the medical opinion on its potential bene fit.Miscellaneous devices and topics 219

To clarify a patient ’s wishes, two documents may be prepared:
▶An advance directive contains instructions regarding
health care decisions, especially in the case of incapa-citation. It can include durable power of attorney and aliving will.
▶Do not resuscitate (DNR) order: A DNR is a patient ’s
instruction not to restart a failed heartbeat or respiration. Itdoes not mean that the patient will not be treated withmedications. Patients who are DNR may still receiveantibiotics and sedation or medications for pain. Do notresuscitate allows for a patient to die naturally if his or her
respiratory or cardiac systems stop working.
STUDY QUESTIONS
1..Identify some children ’s toys that may need BMET support.
Describe the support needed.
2..Discuss the prevalence of fetal monitors in hospitals that
commonly deliver babies.
3..Discuss the prevalence of nurse call systems in hospitals. Giventhis information, discuss why many institutions have adedicated person trained in the system.
4..Describe an example of a commonly used device that anoccupational therapist might ask to be adapted for hospitaluse. Describe the skill the patient would relearn using thisdevice.
5..List possible medical support devices needed by long-termdisabled patients.220 Introduction to Biomedical Instrumentation

FOR FURTHER EXPLORATION
1..Read the January 2008 cover story in 24×7 about BMETs and
play therapy at http://www.24x7mag.com/issues/articles/2008 –
01_01.asp. Summarize the relationship between the BMET,
children ’s toys, and the support of patient play.
2..Research, document, and describe RFID systems used in infantprotection systems (Hugs made by X-mark is a popular brand).How do the alarms or automatic door locks promote infantsafety? Describe the potential concerns of parents regardinginfant “tagging. ”
3..Research, de fine, and describe transcutaneous electrical nerve
stimulators (TENS). How do they work? How do they bene fit
patients?
4..Hyrdrocollator is a brand of device that heats moist pain-reliefpads. Describe and document how they work. How do theybenefit patients?
5..Research, identify, and describe at least five major causes of
permanent disabilities.
6..Google search “assistive devices disabled ”and you will see the
many, many devices available. Document how many aretechnically based (talking computers versus canes andwalkers)? Describe a few of the technical ones. How hasadvancing age of the population expanded the availability of
assistive devices?
7..Describe, document, and evaluate the ethics surrounding the
use of experimental devices in terminally ill patients.
8..Research the Uniform Determination of Death Act 1982,
which forms the legal basis for the recognition of brain deathMiscellaneous devices and topics 221

in the United States. Research, document, and describe how
brain death is determined.
9..Some court cases regarding end-of-life rights and technology
become quite famous. Research and describe the end-of-life
case of Karen Quinlan. How did the court eventually rule?What happened when her ventilator was disconnected?222 Introduction to Biomedical Instrumentation

Index
ACLS (advanced cardiac life support), 88
adult respiration rate, 115
advanced cardiac life support. SeeACLS
AEDs (automated external defibs), 90 –92
AIDS, 44, 146air, make up of, 114airborne precautions, 48
alpha waveform EEG, 129
alveoli, 114, 121American College of Clinical Engineering, 41American Society for Healthcare
Engineering, 27
analog to digital conversion, 63anesthesia monitoring, 130
anesthesiologists, 157
anesthesiology, 158– 59
anesthesia machines, 166
CRNAs and, 160
post-anesthesia care unit (PACU), 165
anesthetizing locations
definition of, 27extension cords and, 32
angioplasty, 183apnea, 116
arthroscopes, 168
artificial hearts, 88, 91. See also heart
Association for the Advancement of
Medical Instrumentation (AAMI),13, 14, 26
asthma, 146
asystole, 73atria, 71
P waves and, 71
atrioventricular node (AV) node, 71
audiology, 218
auscultatory method of measurement, 104
autoclave, 163automated external defibs. SeeAEDs
balloon pumps, 142beta waveform EEG, 129biomedical engineering (BME), 14
Biomedical Engineering Society, 14
Code of Ethics from, 40
biomedical equipment technician. See
BMET
Biomedtalk-L (email listserv), 14
biphasic waveforms, 89
BIS (bispectral index), 130
blood, 44, 167
Coulter technique and, 195
tests on, 195
blood pressure, 55, 82, 104. See also heart
automated equipment to measure, 106,
108
blood pressure cuffs, 104
diastolic pressure, 105errors in measurement, 106
invasive arterial pressure measurement,
109
Korotkoff sounds, 104, 108noninvasive, 104, 106, 108
223

blood pressure ( cont.)
oscillometric method of measuring, 108
sphygmomanometers and, 104
stethoscopes and, 104systolic pressure, 105
waveforms of, 61
BMET
associations, 13, 14, 26certification and, 11 –12
customer service skills needed by, 48 –50
customer service to staff and, 163
definitions of, 2
education requirements, 7
employers of, 3equipment testing and, 42 –43
ethics and, 40 –42
governing bodies, 13hospital employment of, 3 –7
job function categories of, 2magazines for, 13orthopedics and, 165OTs and, 218
patient care and, 2
safety boards and, 7safety precautions, 43 –48
sales, 7sterile fields and, 161telephone support, 7
training classes for, 6
versus biomedical engineering (BME), 14
body fluids, 44
brain. See also cerebellum and cerebrum;
EEG
brainstems, 128
cerebellum and cerebrum, 128
cerebral spinal fluid shunts, 133
EEGs and, 129– 30
lesions, 129
measuring function of, 128
responses to stimuli, 129, 130review of neuroanatomy and
physiology, 128
signals of, 128ventricles of, 128Bundle of His, 71burn ICUs, 147
cannulas, 109
capacitance, 54
capacitive leakage current, 25
capnography, 116carbon dioxide, 116
Cardiac care unit (CCU), 142
cardiac catheterization, 183cardiac/thoracic surgery, 162cardioversion, 90
C-arm devices, 183
CAT (computerized axial tomography),
181
CBET exam, 11, 12CBF (cerebral blood flow), 132CCU (cardiac care unit), 142
ceiling mounted receptacles,
in the operating room, 33
centrifuge, 197– 200
cerebellum and cerebrum, 128. See also
brain
cerebral blood flow (CBF), 132
cerebral perfusion pressure (CPP), 132
cerebral spinal fluid, 128
shunts, 133
certification, 11 –12
childbirth, fetal heart monitoring during,
79
clinical laboratory, 9, 10
electrical outlets in, 32
equipment in, 194
CMV. Seecontinuous mandatory
ventilation
code carts, 142College of American Pathology (CAP), 13Compressed Gas Association (CGA), 13
computed tomography (CT ), 181
computerized axial tomography (CAT), 181conduction abnormalities, 73
contact precautions, 48
continuous mandatory ventilation
(CMV), 119224 Index

continuous positive airway pressure
(CPAP), 119
contrast medium, 185
Coulter technique, 195CPAP. Seecontinuous positive airway
pressure
CPP (cerebral perfusion pressure),
132
CT (computed tomography), 181currents and current leakages, 24
capacitive, 25definitions, 24
earth leakage current, 24
enclosure leakage current, 24fault, 25, 27
grounding systems and, 27
leakage current defined, 24let go current, 21
line isolation monitor, 28
multiple device connections, 27pain current, 21paralysis current, 22
patient auxiliary current, 24
patient leakage current, 24ranges, 22
recommendations for limits, 26
resistive, 25sensors and, 55
threshold current, 21
customer service, 163
skills of, 48 –50
deep vein thrombosis (DVT), 148
defibrillators, 22, 88 –91
AEDs, 90 –92
biphasic waveforms and, 89connecting of, 89implantable, 94
Lown waveforms and, 88
resuscitation and, 142
Delta pressure (Delta-P), 121
delta waveform EEG, 129
diabetes, 210dialysiskidney, 148renal, 148, 219
diastolic pressure, 105DICOM, 185dicrotic notch, 109
digital to analog conversion, 63
Dinamaps, 106drop cords, in the operating room, 33
droplet precautions, 48
DVT. Seedeep vein thrombosis
earth leakage current, 24
fixed equipment and, 26portable equipment and, 26
ECG (electrocardiogram), 58, 59, 61, 71 –79
12-lead monitoring, 76cardioversion and, 90defibrillators and, 90
five-lead monitoring and, 76
long-term recording and, 78MAP and, 109P waves and, 71
patient connections, 76 –78
QRS complex and, 71, 72
T waves and, 71
three-lead monitoring and, 74 –76
use of versus EKG, 71
echocardiography, 179ECLS (extracorporeal life support), 123
ECMO (extracorporeal membrane
oxygenation), 98, 123
education requirements, 7EEG (electroencephologram), 58,
129– 30.See also brain
anesthesia monitoring and, 130
bispectral index (BIS) monitoring, 130
evoked potential testing and, 130intracranial pressure monitoring
(ICP), 130
monitoring problems, 132placement of leads, 130
sleep disorders and, 133
versus ECG, 129
EKG. SeeECGIndex 225

electrical outlets
in clinical lab, 32
emergency power and, 32
hospital grade, 30 –31
electrical shock, 20 –23
in the hospital, 20
electrocardiogram. SeeECG
electrodes, 58 –59
needle, 59scalp, 59surface, 58, 59
electromyograms. SeeEMG
Electronics Technicians Association –
International (ETA-I), 12
electrophoresis, 197
electrosurgical devices. SeeESUs
email listservs, 14
emergency power, 31, 32
emergency response, 88
EMG (electromylogram), 58, 63enclosure leakage current, 24endoscope, 169
endotracheal tube, 121
enteral nutrition, 148, 210epiglottitis, 48
epilepsy, 129
equipment
adaptations and modifications, 6
automated, 108
in clinical laboratory, 194connections, 26
design of, 7
electrosurgical units (ESUs),
169– 72
“fixed, ”26
incoming testing of, 6in laparoscopic surgery, 168 –69
malfunctions of, 6
in operating rooms, 165– 68
repair and troubleshooting, 3
safety board for, 7
sterilization of, 162
testing of, 42 –43
updates, 7ESUs (electrosurgical unit), 169– 72
bipolar, 171
monopolar, 170
ethics, 40 –42
EtO (ethylene oxide) sterilization, 163evoked potential, 130
extension cords
defined, 33
in hospitals, 32
in operating rooms, 32
external respiration, 114
adult respiration rate, 115
apnea, 116
capnography and, 116effectiveness of, 115
exchange of gas in, 114
extracorporeal membrane
oxygenation (ECMO), 123
flow rates in, 115high-frequency ventilation (HFV) and,
120– 23
hyperventilation, 115
hypoventilation, 115
make up of air and, 114make up of expired air and, 114
mechanical ventilation and, 117 –20
pulse oximetry, 116
tidal volume, 114
transthoracic (across the chest)
impedance measurements, 116
volumes of gasses in, 114
external temporary cardiac assist devices, 92
extracorporeal life support (ECLS), 123extracorporeal membrane oxygenation
(ECMO), 98, 123
fault currents, 25, 27
GFCIs and, 28
grounding systems and, 27
LIM alarms and, 28types of, 25
feeding pumps, 210fetal monitoring, 59, 79, 214– 16
fibrillation, 22, 72, 88226 Index

field service representatives. SeeFSRs
fixed equipment, 26
flammable anesthetics, 27
flow cytometry, 195flow rates, 115
fluid analysis, 194
fluid warmers, 167fluoroscopy, 181, 182, 183
Food and Drug Administration (FDA),
Safe Medical Device Act and, 36
FSRs (field service representative), 3, 7 –11
service contracts and, 9, 10travel of, 10
gamma radiation, 187
gasses
exchange of in lungs, 114
volumes of in lungs, 114
GFCIs, 28
gowns, 161
ground impedance, 32
ground pin retention force, 30ground to chassis resis tance measurement, 33
grounding system, 27gynecology, 162
Haemophilus in fluenzae type b disease, 48
Health Insurance Portability and
Accountability Act of, 1996, 36
patient privacy and, 42
heart. See also blood pressure
artificial, 88, 91
cardiac catheterization, 183
echocardiography and, 179electrical signals of, 70 –82
fibrillation and, 22heart rate, 72intraaortic balloon pumps (IABP), 99
microshock and, 23
pacemakers, 93 –94
surgery and, 163valve replacement, 98
heart-lung machines, 96hemoglobin, 79HFOV (high-frequency oscillator
ventilator), 120high-frequency ventilation,
cautions about, 121
high-frequency oscillator ventilator
(HFOV), 120
HIPAA
The Health Insurance Portability and
Accountability Act of, 1996, 36
Holter monitoring, 78
hospitals
BMET employment in, 3 –7
electrical injury in, 20
electrical outlets in, 30, 31
extension cords in, 32
intensive care units and, 140MDR filing, 36
regulation of, 13
sterilization areas, 163
human signals, 61 –65
instrumentation amplification and, 65isolation amplification and, 65periodic, 61random, 62
static, 61
humidifiers, 123
hyperventilation, 115
hypoventilation, 115
hysteresis, 57
IABP (intraaortic balloon pumps), 99
ICP (intracranial pressure monitoring),
130
imaging, 9, 10, 178
angioplasty, 183
cardiac catheterization and, 183C-arm devices and, 183
computed tomography (CT), 181
contrast medium, 185DICOM and, 185
fluoroscopy, 182
MRI (magnetic resonance imaging),
185, 186, 187
PET scans, 187– 88
picture archiving and communication
systems (PACS), 185
ultrasound and, 178– 79
x-rays, 179– 81Index 227

impedance matching, 61, 65
impedance plethysmography, 116
implantable defibrillators, 94
implantable devices, 88in vivo monitoring, 54
incident investigation, 6incoming testing, 6incubators, 143
independent service organization
(ISO), 3
inductance, 54
infants, 123
jaundice treatments, 144neonatal intensive care unit, 143tracking systems, 217
infusion pumps. SeeIV pump
instrumentation amplifier, 65insufflator, 169
insulin pump, 210
intensive care units (ICUs), 210
burn ICU, 147cardiac care units, 142
in hospitals, 140
main characteristics of, 140medical intensive care unit (MICU),
146
monitoring in, 141neonatal intensive care units, 143
neuro-ICUs, 148
pediatric intensive care unit, 146surgical intensive care unit, 147
International Society of Certified
Electronics Technicians (ISCET),12
invasive arterial pressure measurement,
109
ion selective electrodes (ISEs), 195iron lungs, 117
ISEs (ion selective electrodes), 195
isolated power, 28isolation amplifier, 65
isolation transformer, 28
isolation types, 48IV pump, 43, 148, 165, 187, 206 –9jaundice, 144jet ventilator, 120
Joint Commission, 13
Kangaroo Pump, 210
kidney dialysis. Seedialysis
Korotkoff sounds, 104, 108
labor, fetal heart monitoring during,
79
laboratory refrigerators, 201
laparoscopic surgery, 166
equipment used in, 168– 69
laryngoscopes, 121Laser Safety Institute (LSA), 13
LASERs, 9, 172– 73, 184
LDDs (light-detecting diodes), 56
lead placement, ECG, 76 –78
leakage current. Seecurrents and current
leakages
LEDs, 56
colors emitted by, 56
left ventricle assist devices (LVAD), 92let go current, 21life safety code, 34 –36
light-detecting diodes. SeeLDDs
light-emitting diode. SeeLEDs
LIMs, 28
testing of, 28
line isolation monitor. SeeLIMs
linear variable differential transformers.
SeeLVDTs
Lown waveform, 88lungs
exchange of gas in, 114
LVAD (left ventricle assist devices), 92LVDTs, 55
machine/human connection, 54
macroshock, 23magnetic resonance imaging. SeeMRI
make-up of air, 114make-up of expired air, 114mammography, 181228 Index

manuals
vendor supply of, 33 –34
MAP (mean airway pressure), 121
MAP (mean arterial blood pressure),
108
Masimo SET, 82MDR (medical device reporting),
hospitals and, 36
mean airway pressure (MAP), 121mean arterial blood pressure (MAP),
108
measles, 48
mechanical ventilators, 117 –20
alarms and backup systems for, 120
continuous mandatory ventilation,
119
continuous positive airway pressure,
119
Delta pressure (Delta-P), 121high-frequency ventilation (HFV),
120– 23
MAP (mean airway pressure), 121
oxygen concentrations, 120
positive end expiratory pressure, 120respiratory rate and, 119
sensitivity, 120
settings related to, 119synchronized intermittent mandatory
ventilation, 119
Medicaid, 13medical air, 29
Medical Dealer (magazine), 13
medical device reporting. SeeMDR
medical intensive care unit (MICU),
146
Medicare, 13
meningitis, 48mental disorders, 129
mercury gauges, 104
META (Medical Equipment and
Technology Association), 14
microscope
operating, 166
microshock, 23MRI (magnetic resonance imaging), 185
safety of, 186, 187
National Fire Protection Association. See
NFPA
nebulizers, 123needle electrodes, 59, 79Neisseria meningitidis disease, 48
neonatal intensive care unit (NICU), 143
phototherapy and, 144
neonates, 59, 123neuroanatomy and physiology, 128
neuro-ICU, 148
neurology, 162neurons, 128
NFPA (National Fire Protection
Association), 13, 30, 32
Code, 19, 27life safety code, 34 –36
manuals, 33 –34
NIBP. Seenoninvasive blood pressure
NICU. Seeneonatal intensive care unit
nonflammable inhalation anesthetic
agents, 27
noninvasive blood pressure (NIBP), 104,
106, 108
nuclear medicine, 187
nurse call systems, 216
nurses, operating room, 159– 60
circulating, 159
CRNA, 160
scrub, 159
nursing shortage, 106
nutritional support, 148
enteral, 148, 210
parenteral nutrition (hyper-
alimentation), 148
obstetrics, 162
Occupational Health and Safety
Association (OSHA), 13
occupational therapy (OT), 214, 217oncology, 162operating microscopes, 166Index 229

operating rooms, 156
anaesthesiologists and, 157
ceiling mounted receptacles in, 33
drop cords in, 33equipment used in, 165 –68
lights in, 168nurses in, 159– 60
outfit policies, 160
outlet strips in, 33
power cords in, 33pre-op procedures and areas, 157sterile field in, 160– 61
stress of, 163surgical lights, 157surgical technicians in, 160
tables in, 157, 168
ophthalmology, 162
orthopedics, 162
saws and drills used in, 168
oscillator ventilator, 120oscillometric method, 108osmolality, 196– 97
osmometry, 196OT (occupational therapy), 214, 217otolaryngology, 162
outlets
emergency power, red, 31, 32
holding power and, 30
in the operating room, 33
wiring, 30
outside service organization (OSA), 3
oxygen concentrations, 120
oxygen tents, 122
P wave, 71
pacemakers, 93 –94, 143
MRIs and, 186
PACS (picture archiving and
communication systems), 185
pain current, 21
paralysis current, 22
parenteral nutrition (hyper-
alimentation), 148
patient auxiliary current, 24patient care
BMETs and, 2equipment involved in, 2
patient care beds, 150
patient care locations, 29
wet areas and, 30
patient connection, 29patient-controlled analgesia (PCA), 209
patient death
MDR filing and, 36
patient leakage current, 24
patient monitoring, 54
patient privacy, 42
patient safety, 20, 42
electrical shock, 20 –23
PCA (patient-controlled analgesia), 209pediatric intensive care unit (PICU), 146pediatrics, 162
PEEP (positive end expiratory pressure),
120
performance assurance, 4
periodic signals, 61
periodic waveforms, 61
personal protective equipment (PPE), 46PET scans, 132, 187– 88
photo detectors, 56photoemissive devices, 56photocells, 56
photodiode. SeeLDDs
photometry, 196
photoresistors, 55
phototherapy, 144
physical therapy (PT), 218physiological monitor, 106physiological signals. Seehuman signals
picture archiving and communication
systems (PACS), 185
PICU (pediatric intensive care unit), 146
piezoelectric crystals, 55
plastic surgery, 162play therapy, 214
plethysmography. Seeimpedance
plethysmography
plugged-in devices, 26230 Index

PMs (preventative maintenance), 3
pneumonia, 48, 146
point-of-care testing, 201
portable equipment
earth leakage current, 26
positive end expirator y pressure (PEEP), 120
post-anesthesia care unit (PACU), 165potentiometers, 54
potentiometry, 195
power cord ground conductors
ground impedance and, 32wire gauge requirement for, 31
power cords
in the operating room, 33three-wire cords and, 32
PPE. Seepersonal protective equipment
precautions
airborne, 48
contact, 48
droplet, 48transmission-based, 47
pregnancy, 179
pre-op
anaesthesiologists and, 157
areas and procedures, 157
pre-purchase evaluation, 6preventative maintenance. SeePMs
prosthetics, 219
PT (physical therapy), 218
pulse oximetry, 79 –82, 116, 141
apnea and, 116
Masimo SET and, 82
patient movement and, 82readings lower than 90% in, 81
Purkinje network, 71
QRS complex, 71, 72random signals and waveforms, 62, 63
receptacle. Seeoutlet
red electrical outlets, 31, 32
regulatory definitions, 27
renal dialysis. Seedialysis
resistance, 54resistive leakage current, 25respiration. See also external respiration
adult respiration rate, 115
apnea, 116
effectiveness of, 115hyperventilation, 115
pulse oximetry, 116
respiratory rate, 119
respiratory therapists, 115, 119
respiratory therapy
devices used in, 122
resuscitation, 142
retention force, ground pin, 30
return electrode monitor, 170, 171
rhythm disturbances, 73robotics, operating room, 166
SA node, 88
Safe Medical Device Act (1990), 36
safety. Seepatient safety
safety analyzers, 43
safety board, 7safety precautions, 43 –48.See also patient
safety
salaries, 10, 12sales, 7
saws and drills, 168
scalp electrodes, 59scopes, 168
scrub nurses, 159, 160
scrubs, 160sensors, 54 –55, 82
error and unreliability in, 57, 58errors in hospitals, 57hysteresis, 57insertion errors, 57
LVDTs, 55
output changes and, 54photoresistors, 55
piezoelectric crystals, 55
potentiometers, 54strain gauges, 54
temperature and, 60
thermistors, 55thermocouples, 55voltage/current production and, 55Index 231

sepsis, 48
service contracts, 9, 10
SICU (surgical intensive care unit), 147
signal noise, 64SIMV (synchronized intermittent
mandatory ventilation), 119
single photoemission computer
tomography (SPECT), 132
sinoatrial (SA) Node, 71sleep, 130, 159
disorders of, 133lab room, 133
patterns, 129
smoke evacuators, 166
spectrophotometry, 56, 196
sphygmomanometers, 104
spinal cord, 128spirometers, 115
staff support, 6
standard precautions 46. See also
precautions
static signals, 61
sterile field, 160 –61
nurses and, 159
sterilization, 162
in hospitals, 163
strain gauges, 54
surface electrodes, 58, 59
difficulties with, 59
surgery
heart, 163
laparoscopic, 168 –69
post-anesthesia care unit (PACU), 165
specialties and subspecialties in, 162sterilization of surgical equipment, 162
surgical lights, 157
types of, 161
surgical intensive care unit (SICU), 147
surgical technicians, 160
Swan-Ganz catheter, 109synchronized intermittent mandatory
ventilation (SIMV), 119
syringe pumps, 209systolic pressure, 105T wave, 71telemetry. Seewireless medical telemetry
telephone support, 7temperature, 82
patient ranges in, 60
sensors for, 60
terminally ill, 219– 20
thermal dye-dilution, 132thermistors, 55, 60
thermocouples, 55, 60theta waveform EEG, 129threshold current, 21
tidal volume, 114
tissue stainers, 201tracheostomy tube, 122
training classes, 6
transducers. Seesensors
transmission-based precautions, 47
transthoracic (across the chest)
impedance measurements, 116
trochars, 169
tuberculosis, 48, 146
ultrasound, 79, 178 –79
urology, 162VAD. Seeventricular assist devices
valve replacements, 98
varicella (chicken pox), 48
ventilation
endotracheal tubes and, 121
high-frequency ventilation (HFV),
120– 23
in intensive care units, 141
laryngoscopes and, 121
MAP (mean airway pressure), 121
mechanical, 117– 20
patient connection to, 121
settings related to, 119
tracheostomy tubes and, 122
ventricles, 71
intracranial pressure monitoring
(ICP) and, 130
ventricles of the brain, 128232 Index

ventricular assist devices (VAD), 92,
143
vital signs, 70, 106
assumptions about, 70
volumes of gasses, 114
warmers, 123
infant, 143
operating room, 167
Wheatstone bridge circuitry, 54
whirlpool baths, 30white dust, 3wireless medical telemetry, 150, 215
wiring
gauge requirement for power cord
ground conductors, 31
standard colors for, 32
xenon-enhanced computer tomography
(XeCT), 132
x-rays, 179– 81, 183– 85
applications for, 183– 85Index 233