the gale encyclopedia of nursing and allied health.pdf

The GALEENCYCLOPEDIA of

Nursing &Allied Health

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General Index


The GALE ENCYCLOPEDIA of NURSING AND ALLIED HEALTH

STAFF

Kristine Krapp, Coordinating Senior EditorChristine B. Jeryan, Managing EditorDeirdre S. Blanchfield, Associate Editor (Manuscript

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Library of Congress Cataloging-in-Publication DataThe Gale encyclopedia of nursing and allied health / KristineKrapp, editor.p. cm.Includes bibliographical references and index.ISBN 0-7876-4934-1 (set : hardcover : alk. paper)

ISBN 0-7876-4935-X (v. 1 : alk. paper) —ISBN 0-7876-4936-8 (v.2 : alk. paper) —

ISBN 0-7876-4937-6 (v. 3 : alk. paper) — ISBN0-7876-4938-4 (v. 4 : alk. paper) — ISBN 0-7876-4939-2 (v. 5 : alk. paper)

1. Nursing Care—Encyclopedias—English. 2. Allied HealthPersonnel—Encyclopedias—English.3. Nursing—Encyclopedias—English. WY 13 G151 2002]RT21 .G353 2002610.73'03—dc21

2001040910

CONTENTS

GALE ENCYCLOPEDIA OF NURSING AND ALLIED HEALTH V

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vii

Advisory Board. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xi

EntriesVolume 1: A-C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Volume 2: D-H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .641Volume 3: I-O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1237Volume 4: P-S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1797Volume 5: T-Z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2383

Appendix of Nursing and Allied Health

Organizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2663

General Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2669

PLEASE READ—IMPORTANT INFORMATION

The Gale Encyclopedia of Nursing and Allied Healthis a medical reference product designed to inform andeducate readers about a wide variety of diseases, treat-ments, tests and procedures, health issues, human biolo-gy, and nursing and allied health professions. The GaleGroup believes the product to be comprehensive, but notnecessarily definitive. While the Gale Group has madesubstantial efforts to provide information that is accurate,comprehensive, and up-to-date, the Gale Group makes no

representations or warranties of any kind, including with-out limitation, warranties of merchantability or fitness fora particular purpose, nor does it guarantee the accuracy,comprehensiveness, or timeliness of the information con-tained in this product. Readers should be aware that theuniverse of medical knowledge is constantly growingand changing, and that differences of medical opinionexist among authorities.

INTRODUCTION

GALE ENCYCLOPEDIA OF NURSING AND ALLIED HEALTH VII

The Gale Encyclopedia of Nursing and Allied Healthis a unique and invaluable source of information for thenursing or allied health student. This collection of over850 entries provides in-depth coverage of specific dis-eases and disorders, tests and procedures, equipment andtools, body systems, nursing and allied health profes-sions, and current health issues. This book is designed tofill a gap between health information designed forlaypeople and that provided for medical professionals,which may be too complicated for the beginning studentto understand. The encyclopedia does use medical termi-nology, but explains it in a way that students can under-stand.

SCOPE

The Gale Encyclopedia of Nursing and Allied Healthcovers a wide variety of topics relevant to the nursing orallied health student. Subjects covered include thoseimportant to students intending to become biomedicalequipment technologists, dental hygienists, dieteticians,health care administrators, medical technologists/clinicallaboratory sciencists, registered and licensed practicalnurses, nurse anesthetists, nurse practitioners, nurse mid-wives, occupational therapists, optometrists, pharmacytechnicians, physical therapists, radiologic technologists,and speech-language therapists. The encyclopedia alsocovers information on related general medical topics,classes of medication, mental health, public health, andhuman biology. Entries follow a standardized format thatprovides information at a glance. Rubrics include:

Diseases/Disorders

Definition Description Causes and symptoms Diagnosis Treatment Prognosis

Health care team rolesPreventionResourcesKey terms

Tests/Procedures

DefinitionPurposePrecautionsDescriptionPreparationAftercareComplicationsResults Health care team rolesResourcesKey terms

Equipment/Tools

DefinitionPurposeDescriptionOperationMaintenanceHealth care team rolesTrainingResourcesKey terms

Human biology/Body systems

DefinitionDescriptionFunctionRole in human healthCommon diseases and disordersResourcesKey terms

GALE ENCYCLOPEDIA OF NURSING AND ALLIED HEALTHVII I

Nursing and allied health professions

DefinitionDescriptionWork settingsEducation and trainingAdvanced education and trainingFuture outlookResourcesKey terms

Current health issues

DefinitionDescriptionViewpointsProfessional implicationsResourcesKey terms

INCLUSION CRITERIA

A preliminary list of topics was compiled from awide variety of sources, including nursing and alliedhealth textbooks, general medical encyclopedias, andconsumer health guides. The advisory board, composedof advanced practice nurses, allied health professionals,health educators, and medical doctors, evaluated the top-ics and made suggestions for inclusion. Final selection oftopics to include was made by the advisory board in con-junction with the Gale editor.

ABOUT THE CONTRIBUTORS

The essays were compiled by experienced medicalwriters, including physicians, pharmacists, nurses, andallied health care professionals. The advisers reviewedthe completed essays to ensure that they are appropriate,up-to-date, and medically accurate.

HOW TO USE THIS BOOK

The Gale Encyclopedia of Nursing and Allied Healthhas been designed with ready reference in mind.

• Straight alphabetical arrangement of topics allowsusers to locate information quickly.

• Bold-faced terms within entries direct the reader torelated articles.

• Cross-references placed throughout the encyclopediadirect readers from alternate names and related topicsto entries.

• A list of Key terms is provided where appropriate todefine terms or concepts that may be unfamiliar to thestudent.

• The Resources section directs readers to additionalsources of medical information on a topic.

• Valuable contact information for medical, nursing,and allied health organizations is included with eachentry. An Appendix of Nursing and Allied Healthorganizations in the back matter contains an extensivelist of organizations arranged by subject.

• A comprehensive general index guides readers to sig-nificant topics mentioned in the text.

GRAPHICS

The Gale Encyclopedia of Nursing and Allied Healthis enhanced by over 400 black and white photos and illus-trations, as well as over 50 tables.

ACKNOWLEDGMENTS

The editor would like to express appreciation to allof the nursing and allied health professionals who wrote,reviewed, and copyedited entries for the GaleEncyclopedia of Nursing and Allied Health.

Cover photos were reproduced by the permission ofDelmar Publishers, Inc., Custom Medical Photos, and theGale Group.

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ADVISORY BOARD

GALE ENCYCLOPEDIA OF NURSING AND ALLIED HEALTH IX

Dr. Isaac Bankman Principal Scientist Imaging and Laser Systems Section Johns Hopkins Applied Physics Laboratory Laurel, Maryland

Martha G. Bountress, M.S., CCC-SLP/AClinical InstructorSpeech-Language Pathology and AudiologyOld Dominion UniversityNorfolk, Virginia

Michele Leonardi DarbyEminent Scholar, University ProfessorGraduate Program DirectorSchool of Dental HygieneOld Dominion UniversityNorfolk, Virginia

Dr. Susan J. GromackiLecturer in Ophthalmology and Visual SciencesUniversity of Michigan Medical SchoolAnn Arbor, Michigan

Dr. John E. HallGuyton Professor and ChairDepartment of Physiology and BiophysicsUniversity of Mississippi Medical CenterJackson, Mississippi

Lisa F. Harper, B.S.D.H., M.P.H., R.D., L.D.Assistant Professor Baylor College of DentistryDallas, Texas

Robert Harr, M.S. MT (ASCP)Associate Professor and ChairDepartment of Public and Allied HealthBowling Green State UniversityBowling Green, Ohio

Dr. Gregory M. Karst Associate Professor Division of Physical Therapy EducationUniversity of Nebraska Medical Center Omaha, Nebraska

Debra A. Kosko, R.N., M.N., FNP-CInstructor, Faculty PracticeSchool of Nursing, Department of MedicineJohns Hopkins UniversityBaltimore, Maryland

Timothy E. Moore, Ph.D., C PsychProfessor of PsychologyGlendon CollegeYork UniversityToronto, Ontario, Canada

Anne Nichols, C.R.N.P.Coordinator, Family Nurse Practitioner ProgramSchool of NursingWidener UniversityChester, Pennsylvania

Judith B. Paquet, R.N.Medical Communications SpecialistPaquet AssociatesClementon, New Jersey

Lee A. Shratter, M.D.RadiologistHealthcare Safety and Medical ConsultantKentfield, California

Linda Wheeler, C.N.M., Ed.D.Associate ProfessorSchool of NursingOregon Health and Science UniversityPortland, Oregon

A number of experts in the nursing and allied health communities provided invaluable assistance in the formulation of thisencyclopedia. The advisory board performed a myriad of duties, from defining the scope of coverage to reviewing individ-ual entries for accuracy and accessibility. The editor would like to express appreciation to them for their time and their expertcontributions.

CONTRIBUTORS

GALE ENCYCLOPEDIA OF NURSING AND ALLIED HEALTH XI

Lisa Maria Andres, M.S., C.G.CSan Jose, California

Greg AnnussekNew York, New York

Maia ApplebyBoynton Beach, Florida

Bill Asenjo, M.S., C.R.C.Iowa City, Iowa

Lori Ann Beck, R.N., M.S.N., F.N.P.-C.Berkley, Michigan

Mary BekkerWillow Grove, Pennsylvania

Linda K. Bennington, R.N.C., M.S.N., C.N.S.Virginia Beach, Virginia

Kenneth J. Berniker, M.D.El Cerrio, California

Mark A. BestCleveland Heights, Ohio

Dean Andrew Bielanowski, R.N., B.Nurs.(QUT)Rochedale S., Brisbane, Australia

Carole Birdsall, R.N. A.N.P. Ed.D.New York, New York

Bethanne BlackBuford, Georgia

Maggie Boleyn, R.N., B.S.N.Oak Park, Michigan

Barbara BoughtonEl Cerrito, California

Patricia L. Bounds, Ph.D.Zurich, Switzerland

Mary Boyle, Ph.D., C.C.C.-S.L.P., B.C.-N.C.D.Lincoln Park, New Jersey

Rachael Tripi Brandt, M.S.Gettysburg, Pennsylvania

Peggy Elaine BrowningOlney, Texas

Susan Joanne CadwalladerCedarburg, Wisconsin

Barbara M. ChandlerSacramento, California

Linda ChrismanOakland, California

Rhonda Cloos, R.N.Austin, Texas

L. Lee CulvertAlna, Massachusetts

Tish DavidsonFremont, California

Lori De MiltoSicklerville, New Jersey

Victoria E. DeMoranvilleLakeville, Massachusetts

Janine Diebel, R.N.Gaylord, Michigan

Stéphanie Islane DionneAnn Arbor, Michigan

J. Paul Dow, Jr.Kansas City, Missouri

Douglas DuplerBoulder, Colorado

Lorraine K. EhresmanNorthfield, Quebec, Canada

L. Fleming Fallon, Jr., M.D., Dr.P.H.Bowling Green, Ohio

GALE ENCYCLOPEDIA OF NURSING AND ALLIED HEALTHXII

Diane Fanucchi-Faulkner, C.M.T., C.C.R.A.Oceano, California

Janis O. FloresSebastopol, Florida

Paula Ford-MartinChaplin, Minnesota

Janie F. FranzGrand Forks, North Dakota

Sallie Boineau Freeman, Ph.D.Atlanta, Georgia

Rebecca Frey, Ph.D.New Haven, Connecticut

Lisa M. GourleyBowling Green, Ohio

Meghan M. GourleyGermantown, Maryland

Jill Ilene Granger, M.S.Ann Arbor, Michigan

Elliot Greene, M.A.Silver Spring, Maryland

Stephen John Hage, A.A.A.S., R.T.(R), F.A.H.R.A.Chatsworth, California

Clare HanrahanAsheville, North Carolina

Robert HarrBowling Green, Ohio

Daniel J. HarveyWilmington, Delaware

Katherine Hauswirth, A.P.R.N.Deep River, Connecticut

David L. HelwigLondon, Ontario, Canada

Lisette HiltonBoca Raton, Florida

René A. Jackson, R.N.Port Charlotte, Florida

Nadine M. Jacobson, R.N.Takoma Park, Maryland

Randi B. JenkinsNew York, New York

Michelle L. Johnson, M.S., J.D.Portland, Oregon

Paul A. JohnsonSan Marcos, California

Linda D. Jones, B.A., P.B.T.(A.S.C.P.)Asheboro, New York

Crystal Heather Kaczkowski, M.Sc.Dorval, Quebec, Canada

Beth KapesBay Village, Ohio

Monique Laberge, Ph.D.Philadelphia, Pennsylvania

Aliene S. Linwood, B.S.N., R.N., D.P.A., F.A.C.H.E.Athens, Ohio

Jennifer Lee Losey, R.N.Madison Heights, Michigan

Liz MarshallColumbus, Ohio

Mary Elizabeth Martelli, R.N., B.S.Sebastian, Florida

Jacqueline N. Martin, M.S.Albrightsville, Pennsylvania

Sally C. McFarlane-ParrottMason, Michigan

Beverly G. Miller, M.T.(A.S.C.P.)Charlotte, North Carolina

Christine Miner Minderovic, B.S., R.T., R.D.M.S.Ann Arbor, Michigan

Mark A. Mitchell, M.D.Bothell, Washington

Susan M. Mockus, Ph.D.Seattle, Washington

Timothy E. Moore, Ph.D.Toronto, Ontario, Canada

Nancy J. NordensonMinneapolis, Minnesota

Erika J. NorrisOak Harbor, Washington

Debra Novograd, B.S., R.T.(R)(M)Royal Oak, Michigan

Marianne F. O’Connor, M.T., M.P.H.Farmington Hills, Michigan

Carole Osborne-SheetsPoway, California

Con

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GALE ENCYCLOPEDIA OF NURSING AND ALLIED HEALTH XII I

Cindy F. Ovard, R.D.ASpring Valley, California

Patience ParadoxBainbridge Island, Washington

Deborah Eileen Parker, R.N.Lakewood, Washington

Genevieve Pham-KanterChicago, Illinois

Jane E. Phillips, Ph.D.Chapel Hill, North Carolina

Pamella A. PhillipsBowling Green, Ohio

Elaine R. Proseus, M.B.A./T.M., B.S.R.T., R.T.(R)Farmington Hills, Michigan

Ann QuigleyNew York, New York

Esther Csapo Rastegari, R.N., B.S.N., Ed.M.Holbrook, Massachusetts

Anastasia Marie Raymer, Ph.D.Norfolk, Virginia

Martha S. Reilly, O.D.Madison, Wisconsin

Linda Richards, R.D., C.H.E.S.Flagstaff, Arizona

Toni RizzoSalt Lake City, Utah

Nancy Ross-FlaniganBelleville, Michigan

Mark Damian Rossi, Ph.D, P.T., C.S.C.S.Pembroke Pines, Florida

Kausalya SanthanamBranford, Connecticut

Denise L. Schmutte, Ph.D.Shoreline, Washington

Joan M. SchonbeckMarlborough, Massachusetts

Kathleen ScognaBaltimore, Maryland

Cathy Hester Seckman, R.D.H.Calcutta, Ohio

Jennifer E. Sisk, M.A.Havertown, Pennsylvania

Patricia SkinnerAmman, Jordan

Genevieve SlomskiNew Britain, Connecticut

Bryan Ronain SmithCincinnati, Ohio

Allison Joan Spiwak, B.S., C.C.P.Gahanna, Ohio

Lorraine T. SteefelMorganville, New Jersey

Margaret A. Stockley, R.G.N.Boxborough, Massachusetts

Amy Loerch StrumoloBloomfield Hills, Michigan

Liz SwainSan Diego, California

Deanna M. Swartout-Corbeil, R.N.Thompsons Station, Tennessee

Peggy Campbell Torpey, M.P.T.Royal Oak, Michigan

Mai Tran, Pharm.D.Troy, Michigan

Carol A. TurkingtonLancaster, Pennsylvania

Judith Turner, D.V.M.Sandy, Utah

Samuel D. Uretsky, Pharm.D.Wantagh, New York

Michele R. WebbOverland Park, Kansas

Ken R. WellsLaguna Hills, California

Barbara Wexler, M.P.H.Chatsworth, California

Gayle G. Wilkins, R.N., B.S.N., O.C.N.Willow Park, Texas

Jennifer F. WilsonHaddonfield, New Jersey

Angela WoodwardMadison, Wisconsin

Jennifer WurgesRochester Hills, Michigan

Contributors

A

GALE ENCYCLOPEDIA OF NURSING AND ALLIED HEALTH 1

Abdominal thrust see Heimlich maneuver

Abdominal ultrasoundDefinition

Abdominal ultrasound uses high frequency soundwaves to produce two-dimensional images of the body’ssoft tissues, which are used for a variety of clinical appli-cations, including diagnosis and guidance of treatmentprocedures. Ultrasound does not use ionizing radiation to produce images, and in comparison to other diag-nostic imaging modalities, it is low cost, safe, fast, andversatile.

Purpose

Abdominal ultrasound is used in the hospital radiol-ogy department and emergency department, as well as inphysician offices for a number of clinical applications.Ultrasound has a great advantage over x-ray imagingtechnologies in that it does not damage tissues with ion-izing radiation. Ultrasound is also generally far betterthan plain x-rays at distinguishing the subtle variations ofsoft tissue structures, and can be used in any of severalmodes, depending on the area of interest.

As an imaging tool, abdominal ultrasound generallyis indicated for patients afflicted with chronic or acuteabdominal pain; abdominal trauma; an obvious or sus-pected abdominal mass; symptoms of liver disease, pan-creatic disease, gallstones, spleen disease, kidney diseaseand urinary blockage; or symptoms of an abdominal aor-tic aneurysm.

Specifically:

• Abdominal pain. Whether acute or chronic, pain cansignal a serious problem—from organ malfunction orinjury to the presence of malignant growths.

Ultrasound scanning can help doctors quickly sortthrough potential causes when presented with generalor ambiguous symptoms. All of the major abdominalorgans can be studied for signs of disease that appear aschanges in size, shape, and internal structure.

• Abdominal trauma. After a serious accident, such as acar crash or a fall, internal bleeding from injuredabdominal organs is often the most serious threat tosurvival. Neither the injuries nor the bleeding may beimmediately apparent. Ultrasound is very useful as aninitial scan when abdominal trauma is suspected, and itcan be used to pinpoint the location, cause, and severi-ty of hemorrhaging. In the case of puncture wounds,from a bullet for example, ultrasound can locate the foreign object and provide a preliminary survey of the damage. (CT scans are sometimes used in traumasettings.)

• Abdominal mass. Abnormal growths—tumors, cysts,abscesses, scar tissue, and accessory organs—can belocated and tentatively identified with ultrasound. Inparticular, potentially malignant solid tumors can bedistinguished from benign fluid-filled cysts. Massesand malformations in any organ or part of the abdomencan be found.

• Liver disease. The types and underlying causes of liverdisease are numerous, though jaundice tends to be ageneral symptom. Ultrasound can differentiate betweenmany of the types and causes of liver malfunction, andis particularly good at identifying obstruction of thebile ducts and cirrhosis, which is characterized byabnormal fibrous growths and reduced blood flow.

• Pancreatic disease. Inflammation and malformation ofthe pancreas are readily identified by ultrasound, asare pancreatic stones (calculi), which can disrupt prop-er functioning.

• Gallstones. Gallstones are an extremely common causeof hospital admissions. These calculi can cause painfulinflammation of the gallbladder and also obstruct thebile ducts that carry digestive enzymes from the gall-

GALE ENCYCLOPEDIA OF NURSING AND ALLIED HEALTH2

bladder and liver to the intestines. Gallstones are read-ily identifiable with ultrasound.

• Spleen disease. The spleen is particularly prone toinjury during abdominal trauma. It may also becomepainfully inflamed when infected or cancerous.

• Kidney disease. The kidneys are also prone to traumat-ic injury and are the organs most likely to form calculi,which can block the flow of urine and cause furthersystemic problems. A variety of diseases causing dis-tinct changes in kidney morphology can also lead tocomplete kidney failure. Ultrasound imaging hasproven extremely useful in diagnosing kidney disor-ders, including blockage or obstruction.

• Abdominal aortic aneurysm. This is a bulging weakspot in the abdominal aorta, which supplies blooddirectly from the heart to the entire lower body. A rup-tured aortic aneurysm is imminently life-threatening.However, it can be readily identified and monitoredwith ultrasound before acute complications result.

• Appendicitis. Ultrasound is useful in diagnosingappendicitis, which causes abdominal pain.

Ultrasound technology can also be used for treat-ment purposes, most frequently as a visual aid duringsurgical procedures—such as guiding needle placementto drain fluid from a cyst, or to guide biopsies.

Precautions

Ultrasound waves of appropriate frequency andintensity are not known to cause or aggravate any med-ical condition.

The value of ultrasound imaging as a medical tool,however, depends greatly on the quality of the equipmentused and the skill of the medical personnel operating it.More accurate results are obtained when ultrasound isperformed by a clinician skilled in sonography. Basicultrasound equipment is relatively inexpensive to obtain,and any physician with the equipment can perform theprocedure whether specifically trained in ultrasoundscanning and interpretation or not. Patients should nothesitate to verify the credentials of technologists andphysicians performing ultrasound scanning, as well asthe quality of the equipment used and the benefits of theproposed procedure.

In cases where ultrasound is used as a treatment tool,patients should educate themselves about the proposedprocedure with the help of their doctors—as is appropri-ate before any surgical procedure. Also, any abdominalultrasound procedure, diagnostic or therapeutic, may behampered by a patient’s body type or other factors, suchas the presence of excessive bowel gas (which is opaque

to ultrasound). In particular, very obese people are oftennot good candidates for abdominal ultrasound.

Description

Ultrasound includes all sound waves above the fre-quency of human hearing—about 20 thousand hertz, orcycles per second. Medical ultrasound generally uses fre-quencies between one and 10 megahertz (1-10 MHz).Higher frequency ultrasound waves produce moredetailed images, but are also more readily absorbed andso cannot penetrate as deeply into the body. Abdominalultrasound imaging is generally performed at frequenciesbetween 2-5 MHz.

An ultrasound scanner consists of two parts: the trans-ducer and the data processing unit. The transducer bothproduces the sound waves that penetrate the body andreceives the reflected echoes. Transducers are built aroundpiezoelectric ceramic chips. (Piezoelectric refers to elec-tricity that is produced when you put pressure on certaincrystals such as quartz.) These ceramic chips react to elec-tric pulses by producing sound waves (they are transmit-ting waves) and react to sound waves by producing elec-tric pulses (receiving). Bursts of high-frequency electricpulses supplied to the transducer cause it to produce thescanning sound waves. The transducer then receives thereturning echoes, translates them back into electric pulses,and sends them to the data processing unit—a computerthat organizes the data into an image on a television screen.

Because sound waves travel through all the body’stissues at nearly the same speed—about 3,400 miles perhour—the microseconds it takes for each echo to bereceived can be plotted on the screen as a distance intothe body. The relative strength of each echo, a function ofthe specific tissue or organ boundary that produced it, canbe plotted as a point of varying brightness. In this way,the echoes are translated into an image.

Four different modes of ultrasound are used in med-ical imaging:

• A-mode. This is the simplest type of ultrasound inwhich a single transducer scans a line through the bodywith the echoes plotted on screen as a function of depth.This method is used to measure distances within thebody and the size of internal organs.

• B-mode. In B-mode ultrasound, a linear array of trans-ducers simultaneously scans a plane through the body thatcan be viewed as a two-dimensional image on screen.

• M-Mode. The M stands for motion. A rapid sequence ofB-mode scans whose images follow each other insequence on screen enables doctors to see and measurerange of motion, as the organ boundaries that producereflections move relative to the probe. M-mode ultra-

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sound has been put to particular use in studying heartmotion.

• Doppler mode. Doppler ultrasonography includes thecapability of accurately measuring velocities of moving

material, such as blood in arteries and veins. The prin-

ciple is the same as that used in radar guns that measure

the speed of a car on the highway. Doppler capability is

most often combined with B-mode scanning to produce

Abdom

inal ultrasound

Doppler—The Doppler effect refers to the apparentchange in frequency of sound wave echoes return-ing to a stationary source from a moving target. Ifthe object is moving toward the source, the fre-quency increases; if the object is moving away, thefrequency decreases. The size of this frequencyshift can be used to compute the object’s speed—be it a car on the road or blood in an artery. TheDoppler effect holds true for all types of radiation,not just sound.

Frequency—Sound, whether traveling through airor the human body, produces vibrations—mole-cules bouncing into each other—as the shock wavetravels along. The frequency of a sound is the num-ber of vibrations per second. Within the audiblerange, frequency means pitch—the higher the fre-quency, the higher a sound’s pitch.

Ionizing radiation—Radiation that can damage liv-ing tissue by disrupting and destroying individualcells at the molecular level. All types of nuclearradiation—x rays, gamma rays and beta rays—arepotentially ionizing. Sound waves physicallyvibrate the material through which they pass, butdo not ionize it.

Jaundice—A condition that results in a yellow tintto the skin, eyes and body fluids. Bile retention inthe liver, gallbladder and pancreas is the immediatecause, but the underlying cause could be as simpleas obstruction of the common bile duct by a gall-stone or as serious as pancreatic cancer. Ultra-sound can distinguish between these conditions.

Malignant—The term literally means growingworse and resisting treatment. It is used as a syn-onym for cancerous and connotes a harmful condi-tion that generally is life-threatening.

Morphology—Literally, the study of form. In medi-cine, morphology refers to the size, shape, andstructure rather than the function of a given organ.As a diagnostic imaging technique, ultrasoundfacilitates the recognition of abnormal morpholo-gies as symptoms of underlying conditions.

Accessory organ—A lump of tissue adjacent to anorgan that is similar to it, but which serves noimportant purpose, if functional at all. While notnecessarily harmful, such organs can cause prob-lems if they grow too large or become cancerous.

Benign—In medical usage, benign is the oppositeof malignant. It describes an abnormal growth that is stable, treatable, and generally not life-threatening.

Biopsy—The surgical removal and analysis of a tis-sue sample for diagnostic purposes. Usually, theterm refers to the collection and analysis of tissuefrom a suspected tumor to establish malignancy.

Calculus—Any type of hard concretion (stone) inthe body, but usually found in the gallbladder, pan-creas, and kidneys. Calculi (pl.) are formed by theaccumulation of excess mineral salts and otherorganic material such as blood or mucous. Theycan cause problems by lodging in and obstructingthe proper flow of fluids, such as bile to the intes-tines or urine to the bladder.

Cirrhosis—A chronic liver disease characterized bythe degeneration of proper functioning—jaundiceis often an accompanying symptom. Causes of cir-rhosis include alcoholism, metabolic diseases,syphilis, and congestive heart disease.

Common bile duct—The branching passagethrough which bile—a necessary digestiveenzyme—travels from the liver and gallbladder intothe small intestine. Digestive enzymes from thepancreas also enter the intestines through the com-mon bile duct.

Computed tomography scan (CT scan)—A special-ized type of x-ray imaging that uses highly focusedand relatively low energy radiation to producedetailed two-dimensional images of soft tissuestructures, particularly the brain. CT scans are thechief competitor to ultrasound and can yield high-er quality images not disrupted by bone or gas.They are, however, more cumbersome, time con-suming and expensive to perform, and they useionizing radiation.

KEY TERMS


images of blood vessels from which blood flow can bedirectly measured. This technique is used extensively toinvestigate valve defects, arteriosclerosis, and hyper-tension, particularly in the heart, but also in the abdom-inal aorta and the portal vein of the liver.

The actual procedure for a patient undergoing anabdominal ultrasound is relatively simple, regardless ofthe type of scan or its purpose. Fasting for at least eighthours prior to the procedure ensures that the stomach isempty and as small as possible, and that the intestinesand bowels are relatively inactive. This also helps thegallbladder become more visible. Prior to scanning, anacoustic gel is applied to the skin of the patient’sabdomen to allow the ultrasound probe to glide easilyacross the skin and also to better transmit and receiveultrasonic pulses. The probe is moved around theabdomen’s surface to obtain different views of the targetareas. The patient will likely be asked to change posi-tions from side to side and to hold the breath as necessaryto obtain the desired views. Usually, a scan will takefrom 20 to 45 minutes, depending on the patient’s condi-tion and anatomical area being scanned.

Ultrasound scanners are available in different con-figurations, with different scanning features. Portableunits, which weigh only a few pounds and can be carriedby hand, are available for bedside use, office use, or useoutside the hospital, such as at sporting events and inambulances. Portable scanners range in cost from$10,000 to $50,000. Mobile ultrasound scanners, whichcan be pushed to the patient bedside and between hospi-tal departments, are the most common comfiguration andrange in cost from $100,000 to over $250,000, depend-ing on the scanning features purchased.

Preparation

A patient undergoing abdominal ultrasound will beadvised by the physician about what to expect and how toprepare. As mentioned above, preparations generallyinclude fasting.

Aftercare

In general, no aftercare related to the abdominalultrasound procedure itself is required. Discomfort dur-ing the procedure is minimal.

Complications

Properly performed, ultrasound imaging is virtuallywithout risk or side effects. Some patients report feelinga slight tingling and/or warmth while being scanned, butmost feel nothing at all.

Results

As a diagnostic imaging technique, a normal abdom-inal ultrasound is one that indicates the absence of the sus-pected condition that prompted the scan. For example,symptoms such as abdominal pain radiating to the backsuggest the possibility of, among other things, an abdom-inal aortic aneurysm. An ultrasound scan that indicates theabsence of an aneurysm would rule out this life-threaten-ing condition and point to other, less serious causes.

Because abdominal ultrasound imaging is generallyundertaken to confirm a suspected condition, the resultsof a scan often will confirm the diagnosis, be it kidneystones, cirrhosis of the liver, or an aortic aneurysm. Atthat point, appropriate medical treatment as prescribed bya patient’s physician is in order.

Health care team roles

Ultrasound scanning should be performed by a reg-istered and trained ultrasonographer, either a technologistand/or a physician (radiologist, obstetrician/gynecolo-gist). Ultrasound scanning in the emergency departmentmay be performed by an emergency medicine physician,who should have appropriate training and experience inultrasonography.

Resources

BOOKS

Dendy, P.P., Heaton, B. Physics for Diagnostic Radiology. 2nded. Philadelphia: Institute of Physics Publishing, 1999.

Hall, Rebecca. The Ultrasonic Handbook: Clinical, etiologicand pathologic implications of sonographic findings.Philadelphia: Lippincott, 1993.

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An ultrasound screen shows a patient’s kidney.(Photograph by Brownie Harris. The Stock Market.Reproduced by permission.)


Kevles, Bettyann Holtzmann. Naked to the Bone: Medicalimaging in the twentieth century. New Brunswick, NewJersey: Rutgers University Press, 1997.

Zaret, Barry L., ed. The Patient’s Guide to Medical Tests.Boston: Houghton Mifflin Company, 1997.

PERIODICALS

Freundlich, Naomi. “Ultrasound: What’s Wrong with thisPicture?” Business Week (15 September 1997): 84-85.

Kuhn, M., Bonnin, R.L.L., Davey, M.J., Rowland, J.L.,Langlois, S. “Emergency Department UltrasoundScanning for Abdodminal Aortic Aneurysm: Accessible,Accurate, Advantageous. Annals of Emergency Medicine.(September 2000) 36(3):219-223.

Sisk, Jennifer. “Ultrasound in the Emergency Department:Toward a Standard of Care.” Radiology Today (June 4,2001) 2(1):8-10.

ORGANIZATIONS

American College of Radiology. 1891 Preston White Drive,Reston, VA 20191-4397. (800)227-5463..

American Institute of Ultrasound in Medicine. 14750 SweitzerLane, Suite 100, Laurel, MD 20707-5906. (301) 498-4100. .

American Registry of Diagnostic Medical Sonographers. 600Jefferson Plaza, Suite 360, Rockville, MD 20852-1150.(800) 541-9754. .

American Society of Radiologic Technologists (ASRT). 15000Central Avenue SE, Albuquerque, NM 87123-2778. (800)444-2778. .

Radiological Society of North America. 820 Jorie Boulevard,Oak Brook, IL 60523-2251. (630) 571-2670..

Society of Diagnostic Medical Sonography. 12770 Coit Road,Suite 708, Dallas, TX 75251-1319. (972) 239-7367..

Jennifer E. Sisk, M.A.

ABO blood typing see Type and screen

Abrasions see Wounds

Abruptio placentae see Placental abruption

AbscessDefinition

An abscess is an enclosed collection of liquefied tis-sue, known as pus, somewhere in the body. It is the resultof the body’s defensive reaction to foreign material.

Description

There are two types of abscesses, septic and sterile.Most abscesses are septic, which means that they are theresult of an infection. Septic abscesses can occur any-where in the body. Only bacteria and the body’simmune response are required. In response to the invad-ing bacteria, white blood cells gather at the infected siteand begin producing chemicals called enzymes thatattack the bacteria by first marking and then digesting it.These enzymes kill the bacteria and break them downinto small pieces that can travel in the circulatory systemprior to being eliminated from the body. Unfortunately,these chemicals also digest body tissues. In most cases,bacteria produce similar chemicals. The result is a thick,yellow liquid—pus—containing dead bacteria, digestedtissue, white blood cells, and enzymes.

An abscess is the last stage of a tissue infection thatbegins with a process called inflammation. Initially, asinvading bacteria activate the body’s immune system,several events occur:

• Blood flow to the area increases.

• The temperature of the area increases due to theincreased blood supply.

• The area swells due to the accumulation of water,blood, and other liquids.

• It turns red.

• It hurts, due to irritation from the swelling and thechemical activity.

These four signs—heat, swelling, redness, andpain—characterize inflammation.

As the process progresses, the tissue begins to turn toliquid, and an abscess forms. It is the nature of an abscessto spread as the chemical digestion liquefies more andmore tissue. Furthermore, the spreading follows the pathof least resistance, commonly, the tissue that is most eas-ily digested. A good example is an abscess just beneaththe skin. It most easily continues along immediatelybeneath the surface rather than traveling up through theoutermost layer or down through deeper structures whereit could drain its toxic contents. The contents of anabscess can also leak into the general circulation and pro-duce symptoms just like any other infection. Theseinclude chills, fever, aching, and general discomfort.

Sterile abscesses are sometimes a milder form of thesame process caused not by bacteria but by non-livingirritants such as drugs. If an injected drug such as peni-cillin is not absorbed, it stays where it is injected and maycause enough irritation to generate a sterile abscess. Suchan abscess is sterile because there is no infectioninvolved. Sterile abscesses are quite likely to turn into

Abscess


hard, solid lumps as they scar, rather than remainingpockets of pus.

Causes and symptoms

Many different agents cause abscesses. The mostcommon are the pus-forming (pyogenic) bacteria such asStaphylococcus aureus, which is a very common cause ofabscesses under the skin. Abscesses near the large bowel,particularly around the anus, may be caused by any of thenumerous bacteria found within the large bowel. Brainabscesses and liver abscesses can be caused by anyorganism that can travel there through the blood stream.Bacteria, amoebae, and certain fungi can travel in thisfashion. Abscesses in other parts of the body are causedby organisms that normally inhabit nearby structures orthat infect them. Some common causes of specificabscesses are:

• skin abscesses by normal skin flora

• dental and throat abscesses by mouth flora

• lung abscesses by normal airway flora, bacteria thatcause pneumonia or tuberculosis

• abdominal and anal abscesses by normal bowel flora

Specific types of abscesses

Listed below are some of the more common andimportant abscesses.

• Carbuncles and other boils. Skin oil glands (sebaceousglands) on the back or the back of the neck are the onesusually infected. The most commonly involved bacteriais Staphylococcus aureus. Acne is a similar conditioninvolving sebaceous glands on the face and back.

• Pilonidal cyst. Many people have as a birth defect a tinyopening in the skin just above the anus. Fecal bacteriacan enter this opening, causing an infection and subse-quent abscess.

• Retropharyngeal, parapharyngeal, peritonsillar abscess.As a result of throat infections such as strep throat andtonsillitis, bacteria can invade the deeper tissues of thethroat and cause an abscess. These abscesses can com-promise swallowing and even breathing.

• Lung abscess. During or after pneumonia, whether it’sdue to bacteria [common pneumonia], tuberculosis,fungi, parasites, or other bacteria, abscesses can devel-op as a complication.

• Liver abscess. Bacteria or amoeba from the intestinescan spread through the blood to the liver and causeabscesses.

• Psoas abscess. Deep in the back of the abdomen, oneither side of the lumbar spine, lie the psoas muscles.They flex the hips. An abscess can develop in one ofthese muscles, usually when it spreads from the appen-dix, the large bowel, or the fallopian tubes.

Diagnosis

The common findings of inflammation—heat, red-ness, swelling, and pain—easily identify superficialabscesses. Abscesses in other places may produce onlygeneralized symptoms such as fever and discomfort. Ifan individual’s symptoms and the results of a physicalexamination do not help, a physician may have to resortto a battery of tests to locate the site of an abscess.Usually something in the initial evaluation directs thesearch. Recent or chronic disease in an organ suggests itmay be the site of an abscess. Dysfunction of an organ orsystem, for instance seizures or altered bowel function,may provide the clue. Pain and tenderness on physicalexamination are common findings. Sometimes a deepabscess will eat a small channel (sinus) to the surfaceand begin leaking pus. A sterile abscess may cause onlya painful lump deep in the buttock where a shot wasgiven.

Abs

cess

KEY TERMS

Cellulitis—Inflammation of tissue due to infection.

Enzyme—Any of a number of protein chemicalsthat can initiate chemical reactions at body tem-perature.

Fallopian tubes—Part of the internal femaleanatomy that carries eggs from the ovaries to theuterus.

Flora—Living inhabitants of a region or area.

Pyogenic—Capable of generating pus. Strep-tococcus, Staphocococcus, and bowel bacteriaare the primary pyogenic organisms.

Sebaceous glands—Tiny structures in the skin thatproduce oil (sebum). If they become plugged,sebum collects inside and forms a nurturing placefor germs to grow.

Septicemia—The spread of an infectious agentthroughout the body by means of the bloodstream.

Sinus—A tubular channel connecting one bodypart with another or with the outside.


Treatment

Since skin is very resistant to the spread of infection,it acts as a barrier, often keeping the toxic chemicals ofan abscess from escaping the body on their own. Thus,the pus must be drained from the abscess by a physician.The surgeon determines when the abscess is ready fordrainage and opens a path to the outside, allowing thepus to escape. Ordinarily, the body handles the remaininginfection, sometimes with the help of antibiotics orother drugs. The surgeon may leave a drain (a piece ofcloth or rubber) in the abscess cavity to prevent it fromclosing before all the pus has drained out.

Alternative treatment

If an abscess is directly beneath the skin, it will beslowly working its way through the skin as it is more rap-idly working its way elsewhere. Since chemicals workfaster at higher temperatures, applications of hot com-presses to the skin over the abscess will hasten the diges-tion of the skin and eventually result in its break downand spontaneous release of pus. This treatment is bestreserved for smaller abscesses in less sensitive areas ofthe body such as limbs, trunk, and back of the neck. It isalso useful for all superficial abscesses in their very earlystages. It will “ripen” them.

Contrast hydrotherapy, alternating hot and coldcompresses, can also help assist the body in resorption ofthe abscess. There are two homeopathic remedies thatwork to rebalance the body in relation to abscess forma-tion, Silica and Hepar sulphuris. In cases of septicabscesses, bentonite clay packs (bentonite clay and asmall amount of Hydrastis powder) can be used to drawan infection from the area.

Prognosis

Once an abscess is properly drained, the prognosis isexcellent for the condition itself. The reason for theabscess (other diseases an individual has) will determinethe overall outcome. If, on the other hand, an abscessruptures into neighboring areas or permits the infectiousagent to spill into the bloodstream, serious or fatal con-sequences are likely. Abscesses in and around the nasalsinuses, face, ears, and scalp may work their way into thebrain. Abscesses within an abdominal organ such as theliver may rupture into the abdominal cavity. In eithercase, the result is life threatening. Blood poisoning is aterm commonly used to describe an infection that hasspilled into the blood stream and spread throughout thebody from a localized origin. Blood poisoning, known tophysicians as septicemia, is also life threatening.

Of special note, abscesses in the hand are more seri-ous than they might appear. Due to the intricate structureand the overriding importance of the hand, any handinfection must be treated promptly and competently.

Health care team roles

First aid providers may unknowingly initiate anabscess by using inappropriate or incorrect techniques. Aphysician, surgeon, physician’s assistant, or nurse practi-tioner usually diagnoses the presence of an abscess.Radiologists and laboratory personnel may assist in theprocess of establishing a diagnosis. A physician, surgeon,physician’s assistant, or nurse practitioner usually drainsan abscess. Nurses provide supportive care, dress thewound, and educate patients about caring for the result-ing wound. Occasionally, a physical therapist may beneeded to recover lost function.

Prevention

Infections that are treated early with heat (if superfi-cial) or antibiotics will often resolve without the forma-tion of an abscess. It is even better to avoid infectionsaltogether by taking prompt care of open injuries, partic-ularly puncture wounds. Bites are the most dangerous ofall, even more so because they often occur on the hand.

Resources

BOOKS

Balistreri, William. “Liver abscess.” In Nelson Textbook ofPediatrics, 16th ed., edited by Richard E. Behrman et al.,Philadelphia, Saunders, 2000, 1212.

Chesney, Russell W. “Brain abscess.” In Nelson Textbook ofPediatrics, 16th ed., edited by Richard E. Behrman et al.,Philadelphia, Saunders, 2000, 1857-1858.

Abscess

An amoebic abscess caused by Entameoba histolytica.(Phototake NYC. Reproduced by permission.)


Finegold, Sydney M. “Lung abscess.” In Cecil Textbook ofMedicine, 21st ed., edited by Goldman, Lee and Bennett,J. Claude. Philadelphia: W.B. Saunders, 2000, 439-442.

Herendeen, Neil E and Szilagy, Peter G. “Peritonsillarabscess.” In Nelson Textbook of Pediatrics, 16th ed., edit-ed by Richard E. Behrman et al., Philadelphia, Saunders,2000, 1266-1267.

Scheld, W. Michael. “Bacterial meningitis, brain abscess, andother suppurative intracranial infections.” In Harrison’sPrinciples of Internal Medicine, 14th ed., edited byAnthony S. Fauci, et al. New York: McGraw-Hill, 1998,2419-2434.

Schwartz, Seymour, Shires, Tom and Spencer, FrankC.Principles of Surgery, 7th ed. New York, McGraw Hill,1998.

Stern, Robert C. “Pulmonary abscess.” In Nelson Textbook ofPediatrics, 16th ed., edited by Richard E. Behrman et al.,Philadelphia, Saunders, 2000, 1309-1310.

Townsend, Courtney M. Sabiston Textbook of Surgery: TheBiological Basis of Modern Surgical Practice, 16th ed.Philadelphia, Saunders, 2001.

PERIODICALSBalatsouras DG, Kloutsos GM, Protopapas D, Korres S,

Economou C. “Submasseteric abscess.” Journal ofLaryngology and Otology 115, no. 1 (2001): 68-70.

Chua, F. “Clinical picture: paravertebral abscess.” Lancet 357,no. 9251 (2001): 168-70.

Rockwell PG. “Acute and chronic paronychia.” AmericanFamily Physician 63, no. 6 (2001): 1113-6.

Struk DW, Munk PL, Lee MJ, Ho SG, Worsley DF. “Imagingof soft tissue infections.” Radiology Clinics of NorthAmerica 39, no. 2 (2001): 277-303.

Taiwo B. “Psoas abscess: a primer for the internist.” SouthernMedical Journal 94, no. 1 (2001): 2-5.

ORGANIZATIONSAmerican Academy of Family Physicians, 11400 Tomahawk

Creek Parkway, Leawood, KS 66211-2672. (913) 906-6000. . [email protected].

American Society of Clinical Pathologists, 2100 WestHarrison Street, Chicago IL 60612. (312) 738-1336.. [email protected].

College of American Pathologists, 325 Waukegan Road,Northfield, IL 60093. (800) 323-4040..

OTHERAmerican Society of Colon and Rectal Surgeons.

.Merck Manual. .South Bank University. .Tuberculosis.Net. .University of Bristol. .

University of California-San Diego:.

University of Kansas Medical Center..

L. Fleming Fallon, Jr., MD, DrPH

Achromatopsia see Color blindness

Acid-base balanceDefinition

Acid-base balance can be defined as homeostasis ofthe body fluids at a normal arterial blood pH rangingbetween 7.37 and 7.43.

Description

An acid is a substance that acts as a proton donor. Incontrast, a base, also known as an alkali, is frequentlydefined as a substance that combines with a proton toform a chemical bond. Acid solutions have a sour tasteand produce a burning sensation with skin contact. A baseis any chemical compound that produces hydroxide ionswhen dissolved in water. Base solutions have a bittertaste and a slippery feel. Despite variations in metabo-lism, diet, and environmental factors, the body’s acid-base balance, fluid volume, and electrolyte concentrationare maintained within a narrow range.

Function

Many naturally occurring acids are necessary forlife. For example, hydrochloric acid is secreted by thestomach to assist with digestion. The chemical composi-tion of food in the diet can have an effect on the body’sacid-base production. Components that affect acid-basebalance include protein, chloride, phosphorus, sodium,potassium, calcium, and magnesium. In addition, therate at which nutrients are absorbed in the intestine willalter acid-base balance.

Cells and body fluids contain acid-base buffers,which help prevent rapid changes in body fluid pH overshort periods of time, until the kidneys pulmonary sys-tems can make appropriate adjustments. The kidneys andpulmonary system then work to maintain acid-base bal-ance through excretion in the urine or respiration. Thepartial pressure of carbon dioxide gas (PCO2) in the pul-monary system can be measured with a blood sample and

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correlates with blood carbon dioxide (CO2) levels. PCO2can then be used as an indicator of the concentration ofacid in the body. The concentration of base in the bodycan be determined by measuring plasma bicarbonate(HCO3-) concentration. When the acid-base balance isdisturbed, the respiratory system can alter PCO2 quick-ly, thus changing the blood pH and correcting imbal-ances. Excess acid or base is then excreted in the urine bythe renal system to control plasma bicarbonate concen-tration. Changes in respiration occur primarily in minutesto hours, while renal function works to alter blood pHwithin several days.

Role in human health

Production of CO2 is a result of normal body metab-olism. Exercise or serious infections will increase theproduction of CO2 through increased respiration in thelungs. When oxygen (O2) is inhaled and CO2 is exhaled,the blood transports these gases to the lungs and body tis-sues. The body’s metabolism produces acids that arebuffered and then excreted by the lungs and kidneys tomaintain body fluids at a neutral pH. Disruptions in CO2levels and HCO3- create acid-base imbalances. Whenacid-base imbalances occur, the disturbances can bebroadly divided into either acidosis (excess acid) or alka-losis (excess base/alkali).

Common diseases and disorders

Acid-base metabolism imbalances are often charac-terized in terms of the HCO3-/CO2 buffer system. Acid-base imbalances result primarily from metabolic or res-piratory failures. An increase in HCO3- is called meta-bolic alkalosis, while a decrease in the same substance iscalled metabolic acidosis. An increase in PCO2, on theother hand, is known as respiratory acidosis, and adecrease in the same substance is called respiratory alka-losis.

Acidosis

Acidosis is a condition resulting from higher thannormal acid levels in the body fluids. It is not a disease,but may be an indicator of disease. Metabolic acidosis isrelated to processes that transform food into energy andbody tissues. Conditions such as diabetes, kidney failure,severe diarrhea, and poisoning can result in metabolicacidosis. Mild acidosis is often compensated by the bodyin a number of ways. However, prolonged acidosis canresult in heavy or rapid breathing, weakness, andheadache. Acidemia (arterial pH < 7.35) is an accumula-tion of acids in the bloodstream that may occur withsevere acidosis when the acid load exceeds respiratorycapacity. This condition can sometimes result in coma

and, if the pH falls below 6.80, it will lead to death.Diabetic ketoacidosis is a condition where excessiveglucagon and a lack of insulin contribute to the produc-tion of ketoacids in the liver. This condition can becaused by chronic alcoholism and poor carbohydrateutilization.

Respiratory acidosis is caused by the lungs’s failureto remove excess carbon dioxide from the body, reducing

Acid-base balance

KEY TERMS

Acid—(a) Any ionic or molecular substance thatcan act as a proton donor; (b) A sour-tasting sub-stance, like vinegar; (c) A chemical compoundthat can react with a base to form a salt.

Acidosis—A dangerous condition where theblood and body tissues are less alkaline (or moreacidic) than normal.

Alkalosis—Excessive alkalinity of the blood andbody tissue.

Alkalemia—Abnormal blood alkalinity.

Base—(a) Any ionic or molecular substance thatcan act as a proton acceptor; (b) A bitter-tastingsubstance which has a soapy feel; (c) A chemicalcompound that can react with an acid to form asalt. A base can also be called an alkali.

Bicarbonate—A salt of carbonic acid produced byneutralizing a hydrogen ion.

Diabetic ketoacidosis—A condition characterizedby excessive thirst and urination. Other symptomsmay include appetite loss, nausea, vomiting, andrapid deep breathing.

Diuretic—An agent or drug that eliminates exces-sive water in the body by increasing the flow ofurine.

Electrolyte—A substance such as an acid, bases,or salt. An electrolyte’s water solution will con-duct an electric current and ionizes. Acids, bases,and salts are electrolytes.

Homeostasis—An organism’s regulation of bodyprocesses to maintain internal equilibrium in tem-perature and fluid content.

Hypochloremic alkalosis—A large loss of chloride.

Hypokalemic alkalosis—Low plasma potassium.

pH—The negative logarithm of H+ (hydrogen)concentration.


the pH in the body. Several conditions, including chestinjury, blockage of the upper air passages, and severelung disease, may lead to respiratory acidosis. Blockageof the air passages may be caused by bronchitis, asthma,or airway obstruction, resulting in mild or severe acido-sis. Regular, consistent retention of carbon dioxide in thelungs is referred to as chronic respiratory acidosis. Thisdisorder results in only mild acidosis because it is bal-anced by increased bicarbonate production.

The predominant symptoms of acidosis are some-times difficult to distinguish from symptoms of an under-lying disease or disorder. Mild conditions of acidosis maybe asymptomatic or may be accompanied by weakness orlistlessness, nausea, and vomiting. Most often, severemetabolic acidosis (pH < 7.20) is associated withincreased respiration to compensate for a shortage ofHCO3-. This is followed by a secondary decrease in PCO2that occurs as part of respiratory compensation process.Treatment options for acidosis typically require correc-tion of the underlying condition by venous administrationof sodium bicarbonate or another alkaline substance.

Alkalosis

Alkalosis is a condition resulting from a higher thannormal level of base/alkali in the body fluids. An exces-sive loss of HCO3- in the blood causes metabolic alkalo-sis. The body can compensate for mild alkalinity, butprolonged alkalosis can result in convulsions, muscularweakness, and even death if the pH rises above 7.80.Alkalosis can be caused by drugs or disorders that upsetthe normal acid-base balance. Prolonged vomiting andhyperventilation (abnormally fast, deep breathing) canresult in alkalosis.

The predominant symptoms of alkalosis are neuro-muscular hyperexcitability and irritability. Alkalemia(abnormal blood alkalinity) increases protein binding ofionized calcium even though plasma total calcium doesnot change. Severe cases may induce hypocalcemia (a

low level of plasma calcium). Low plasma potassiumleads to a condition called hypokalemic alkalosis. It isfrequently accompanied by metabolic alkalosis, resultingin cramping, muscle weakness, polyuria, and ileus(obstruction of the intestines). Diuretic medications maycause hypokalemic alkalosis. Prolonged vomiting mayinduce hypochloremic alkalosis (a large loss of chloride).The kidneys may conserve bicarbonate in order to com-pensate for the chloride reduction. Compensated alkalo-sis results when the body has partially compensated foralkalosis, and has restored normal acid-base balances.However, in compensated alkalosis, abnormal bicarbon-ate and carbon dioxide levels persist.

Alkalosis requires correction of the underlying con-dition and may involve venous administration of a weakacid to restore normal balance. If the source of alkalosisis excessive drug intake, it may be appropriate to reduceintake to restore the normal acid-base balance.

Respiratory alkalosis results from decreased CO2levels caused by conditions such as hyperventilation (afaster breathing rate), anxiety, and fever. The pH is ele-vated in the body. Hyperventilation causes the body tolose excess carbon dioxide in expired air and can be trig-gered by altitude or a disease that reduces the amount ofoxygen in the blood. Symptoms of respiratory alkalosismay include dizziness, lightheadedness, and numbing ofthe hands and feet. Treatments include breathing into apaper bag or a mask that induces rebreathing of carbondioxide.

Resources

BOOKS

Shaw, Patricia, ed. Fluids & Electrolytes Made IncrediblyEasy! Springhouse, PA: Springhouse Publishing Co.,1997.

PERIODICALS

Remer, T. “Influence of diet on acid-base balance.” Seminarsin Dialysis 13, no. 4 (2000): 221–226.

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Respiratory acidosis Respiratory depression (drugs, central nervous systemtrauma)

Pulmonary disease (pneumonia, chronic obstructive pul-monary disease, respiratory underventilation)

Kidneys will retain increased amounts of HCO3– to increase pH

Acid-base disturbances, causes, and compensatory mechanisms

Acid-base disturbance Common cause Mode of compensation

Respiratory alkalosis Hyperventilation (emotions, pain, respirator overventilation)

Kidneys will excrete increased amounts of HCO3– to lower pH

Metabolic acidosis Diabetes, shock, renal failure, intestinal fistula Lungs “blow off” CO2 to raise pH

Metabolic alkalosis Sodium bicarbonate overdose, prolonged vomiting,nasogastric drainage

Lungs retain CO2 to lower pH

SOURCE: Pagana, K.D. and T.J. Pagana. Mosby’s Diagnostic and Laboratory Test Reference. 3rd ed. St. Louis: Mosby, 1997.


OTHER

Bookallil, Michael. “pH of the blood: acid-base balance.”.

Grogono, Alan. “Acid-base tutorial.” .

Crystal Heather Kaczkowski, MSc.

Acid-fast cultureDefinition

The term acid-fast refers to a type of organism notreadily decolorized by acid after staining. An acid-fastculture is the microbiological analysis of such an organ-ism. An acid-fast culture refers to the process of detec-tion, growth, isolation, identification, and antibiotic sus-ceptibility testing of mycobacteria that cause pulmonarytuberculosis and other infections such as skin, abdomi-nal, and disseminated (widely spread throughout manyorgans).

Purpose

The acid-fast culture is used to isolate Mycobacteri-um tuberculosis when tuberculosis (TB) is suspected.More recently the test has become important for the iden-tification of other acid-fast organisms includingMycobacterium avium complex (MAC), Mycobacteriumbovis, and Mycobacterium africanum responsible forcausing tuberculosis in AIDS patients and other immuno-suppressed persons. Antibiotic sensitivity testing per-formed when cultures are positive or when patients areknown to have tuberculosis determines the appropriatedrugs for treatment. This is essential because of theemergence of tuberculosis strains that are resistant tomany of the antibiotics that were once effective in treat-ing this disease. The test is also used to differentiatetuberculosis from carcinoma and bronchiectasis that mayappear similar on x ray.

Precautions

Antibiotics and some sulfonamides may interferewith test results, causing the results to be falsely nega-tive. Sufficient organisms may not be recovered to diag-nose infection when a single culture sample is collected.Therefore, sputum cultures should be collected on threeconsecutive mornings.

Special safety precautions

Health care workers involved with collection andhandling of specimens from patients suspected of havingtuberculosis or other mycobacterial infections shouldobserve universal precautions for the prevention oftransmission of bloodborne pathogens. In addition,health care personnel working with patients and handlingspecimens from patients suspected of having tuberculosismust be given a skin test (e.g. Mantoux or PPD test) on aregular basis. Precautions must be followed closely whenhandling mycobacterial specimens. The laboratory per-sonnel who process and handle the infectious materialfrom the patient are at greatest risk (about three timeshigher than other laboratory personnel) for tuberculosisinfection or skin test positivity. The hazard of working ina laboratory that handles mycobacterial specimens isgreatly reduced if the personnel follow proper procedureswhen handling and processing the specimens. All pro-cessing should take place in a biologic safety cabinet(BSC). The biologic safety cabinets used in the clinicalmycobacterial laboratory are of two types: Class I, ornegative-pressure cabinets, and Class II, or vertical-lam-inar-flow cabinets. Correct operation of these safetydevices along with proper maintenance and testing of theair flow are essential to their performance. Yearly inspec-tion of the cabinets by trained individuals is required.

Processing specimens, testing organisms, and trans-ferring viable cultures must be carried out within theBSC. After processing specimens or working under theBSC, the area inside the cabinet is disinfected and a UV(ultraviolet) light located within the cabinet is turned onto kill any organisms on the surface of the work area aswell as any airborne bacteria. After performing a proce-dure, the work area must be decontaminated with a dis-infectant solution (e.g., the use of a phenol-soap mixturecontaining orthophenol or phenolic derivitives with aneffective contact time of 10-30 minutes).

Protective clothing including gloves, fluid-proofgowns, goggles, and face mask or respirator is recom-mended for laboratory personnel working in the mycobac-terial laboratory. Incinerators (no bunsen burners) are usedwithin the BSC to reduce aerosoling of bacteria frominfectious material while processing and culturing.

Description

Tuberculosis is an infection caused by Mycobac-terium tuberculosis, a disease which is a major healthproblem worldwide. Mycobacterium tuberculosis is arod-shaped bacterium characterized by acid-fastness. It iscommonly transmitted via the air to the lungs, where itthrives, causing fever, cough, and hemoptysis (coughingup blood-tainted secretions). Tuberculosis is highly con-

Acid-fast culture


tagious. Disease is spread when persons cough, releasingan aerosol of organisms that are easily inhaled by others.Although deaths from tuberculosis in the United Stateshad declined since the 1950s, recently there has been aresurgence of the disease, with the higher incidence ofinfection seen in certain races, in poor socioeconomicconditions, among new immigrants, in prison inmates,and in persons infected with the human immunodefi-ciency virus.

Because it takes several weeks for most Mycobac-teria to grow in a culture, the laboratory performs anacid-fast smear first to aid in early diagnosis; however,the acid-fast smear should not be used in place of culture,as a culture is far more sensitive. An acid-fast culture candetect as few as 10 to 100 CFU/mL of sputum. The smearcan provide a presumptive diagnosis of mycobacterialdisease; confirm that cultures growing on media are acid-fast; and demonstrate that antibiotic treatment is effectivepending follow-up culture results.

The genus Mycobacterium includes organisms thatare obligate parasites, saprophytes (i.e., organisms thatlive off dead tissue), and opportunistic pathogens.Mycobacteria cause tuberculosis as well as non-tubercu-lous clinical conditions; therefore, mycobacteria aredivided into two major groups based upon whether theycause tuberculosis (M. tuberculosis complex) or non-tuberculous infections (NTM). The principle pathogencausing tuberculosis in humans is Mycobacterium tuber-culosis. It is estimated that about one third of the world’spopulation is infected with M. tuberculosis. The WorldHealth Organization reports an estimated eight millionnew cases and three million deaths attributable to tuber-culosis each year. Tuberculosis is a leading cause of deathin developing countries.

Other organisms causing human tuberculosis that areincluded in the M. tuberculosis complex are: M. bovis(the cause of tuberculosis in cattle and humans, as well asother carnivores); M. bovis BCG (a strain used as a vac-cine against tuberculosis in many parts of the world); and

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KEY TERMS

Bronchiectasis—The formation of dilated, enlargedbronchi that results from lower respiratory tractinfection.

Granuloma—Encapsulation of infected tissuecaused by phagocytic cells that surround the fociof infection.

Nosocomial—An infection acquired in a hospitalsetting.

M. africanum (the cause of human tuberculosis in tropi-cal Africa). Mycobacterium tuberculosis causes an infec-tion that may mimic other diseases such as pneumonia,neoplasm, or fungal infections. Patients may be sympto-matic or asymptomatic with signs of pulmonary andother organ involvement. Symptoms include nightsweats, low-grade fever, anorexia, fatigue, weight loss,and a productive cough or coughing of blood in pul-monary tuberculosis infections. Patients with HIV aremore likely to develop active tuberculosis.

It is necessary to identify the tuberculosis-causingmycobacteria by species and determine the antibioticsensitivity or resistance-pattern for epidemiologic andpublic health information as well as for the effectivetreatment of infected persons. As stated earlier, aboutone-third of the world’s population (1.7 billion persons)are infected with M. tuberculosis. Therefore, it is of greatconcern that the emergence of epidemic multidrug-resist-ant strains of M. tuberculosis has increased at the sametime as the increase in HIV infections in the UnitedStates.

The primary routes of transmission for the M. tuber-culosis complex are via inhalation of airborne dropletsfrom an infected person; through infectious aerosols pro-duced when processing clinical specimens for the recov-ery of Mycobacteria spp.; and by ingestion of contami-nated milk from cows (or goats) infected with M. bovis.M. africanum is also transmitted by the inhalation ofdroplets containing infecting organisms. In all cases,close contact with infected individuals leads to the acqui-sition of tuberculosis infection.

The nontuberculous mycobacteria (NTM) group,which are not transmitted by person to person contact asis the M. tuberculosis complex, are differentiated by rateof growth (slow-growing or rapid-growing) as well ascolor pigmentation (the ability or inability of the coloniesto change color when exposed to light). Growth patternsare divided into two main groups: slow-growers andrapid growers. Slow growers take more than seven daysto grow and form colonies on solid media; rapid-growersproduce colonies on solid media within three to five days.This method of classification for the NTM, by growthpatterns and exposure to light, is referred to as theRunyon Classification. Some organisms in this group areconsidered pathogenic, and others are potentially patho-genic or non-pathogenic.

One of the most often recovered mycobacteriumspecies in the United States belongs to the NTM groupand is referred to as the Mycobacterium avium complex(MAC). The MAC group consists of two main species,M. avium and M. intracellulare. These two mycobacteriaare very similar and are differentiated by DNA tests. The


MAC organisms are frequently isolated from immuno-compromised patients, such as patients infected withHIV and patients with pre-existing pulmonary disease.MAC infections have been found to be the most commoncause of NTM (nontuberculous mycobacteria) infectionsin humans. The NTM organisms are found in the envi-ronment (frequently recovered from water, soil, housedust, and plants) and are sometimes found colonized inthe respiratory or gastrointestinal tract of healthy indi-viduals. In AIDS patients, MAC infections may be focalor disseminated. It is theorized that the MAC organisms,acquired from the environment, colonize the respiratorytract or gastrointestinal tract before disseminating in anHIV-positive patient. Sputum and stool samples fromHIV infected patients often contain MAC organisms.

Pulmonary disease in AIDS patients due to MACcannot be distinguished clinically or by x ray from thosecaused by M. tuberculosis. Infections caused by dissem-inated MAC organisms in AIDS patients usually occurabout one year after the diagnosis of AIDS. Also, non-AIDS patients who are white males, 45-60 years of age,typically heavy smokers, or alcohol abusers with pre-existing lung disease are good candidates for a tubercu-losis-like disease also caused by MAC organisms.

An NTM, which will not grow in vitro (non-culti-vatable), is M. leprae. Mycobacterium leprae is the causeof leprosy, or Hansen’s disease. This organism causes achronic, debilitating, and disfiguring disease involvingthe skin, mucous membranes, and nerve tissue. There isoften extensive damage to the skin (lesions) and nerves.Infectivity is low and transmission can occur from per-son to person through contact with infected skin; howev-er, inhalation of nasal secretions from the infected person(close contact) appears to be the predominant mode oftransmission. Leprosy in North America is rare, and mostof the cases are acquired from exposure to the organismwhile in a tropical country. Mycobacterium leprae cannotbe cultured on solid or liquid media in vitro; therefore, itis diagnosed by DNA amplification tests such as thepolymerase chain reaction (PCR) using infected tissue,or mucous membrane secretions, and by observing acid-fast bacilli (using acid-fast staining procedures) in thetissue preps or skin biopsies of infected patients.

Several other NTM (non-tuberculous mycobacteria)organisms are considered potential pathogens forhumans while others are rarely implicated in disease. Thefollowing NTM are considered potential pathogens andshould be identified especially if recovered fromimmunocompromised patients:

• Mycobacterium kansasii: A slow grower, causing achronic pulmonary disease resembling classic tubercu-

losis as well as cervical lymphadenitis and cutaneousdiseases; tap water is the main reservoir for humans.

• Mycobacterium haemophilum: A slow grower, causingskin nodules and disseminated disease in immunosup-pressed patients with AIDS, Hodgkins’s disease, andkidney and bone marrow transplants, as well as cervi-cal lymphadenitis in children.

• Mycobacterium marinum: A slow grower, causing cuta-neous infections such as “swimming pool granuloma”and “fish tank granuloma” with its natural reservoirbeing fresh and salt water from infected fish and othermarine life.

• Mycobacterium ulcerans: A slow grower, infecting theskin (usually after some trauma) causing nodules andulcers to form; infection occurs mainly in tropical andtemperate climates (Africa and Australia) and is rare inthe United States.

• Mycobacterium xenopi: A slow grower, causing pul-monary infections in adults (resembling MTB complexand MAC complex). The infection is considered noso-comial, since it is recovered from hospital water stor-age systems and hot and cold taps quite often.

• Mycobacterium scrofulaceum: A slow grower responsi-ble for cervical adenitis in children, recovered from rawmilk, soil, water, and dairy products.

• Mycobacterium szulgai: A slow grower causing pul-monary disease similar to M. tuberculosis.

• Mycobacterium fortuitum complex: Rapid growingmicroorganisms which include M. fortuitum, M.abscessus, and M. chelonae causing infections involv-ing surgical wounds, post-traumatic wound infection,otitis media, and chronic pulmonary disease.

Mycobacterium gordonae is the non-pathogenicmycobacterium most commonly recovered from patientspecimens. It is found in the environment and is calledthe “tap water bacillus.” It is only rarely implicated as acause of human infection.

Specimen collection

Specimens to be processed for the recovery ofmycobacteria are obtained and handled using specificguidelines to ensure successful growth, isolation, andidentification of the causative organism. Containers mustbe sterile, leak-proof, and labeled properly. After collec-tion, if the specimen cannot be processed within onehour, refrigeration is required but no longer thanovernight. However, blood samples must be placed in theproper media and incubated immediately at 35-37°C.

The most often requested specimens are pulmonaryspecimens (secretions) which must be obtained before

Acid-fast culture


any treatment (antibiotic therapy) is given. Pulmonaryspecimens may be obtained in several ways: sponta-neously produced (expectorated) sputum; aerosol-induced sputum; bronchioscopic aspirations, washingsand brushings; gastric aspirates, and lavages (washings)from patients who have swallowed sputum through thenight. Saliva is not acceptable as a specimen for therecovery of mycobacteria and is usually rejected as acontaminated specimen. A series of early morning spu-tum specimens are recommended over a three-day peri-od. The ideal amount of sputum specimen for processingand recovery of mycobacteria is 5-10 mL of sputum.Upon rising in the morning, the patient is instructed tocough deeply to produce sputum (expectorated sputum).A patient who is unable to bring up any sputum is givenan aerosol treatment (aerosol-induced sputum) by a res-piratory therapist in order to recover a sufficient amountof sputum for culture.

Other specimens requested for culture and recoveryof mycobacteria are early morning, voided urine speci-mens; fecal specimens; tissue and body fluids (pleural,pericardial and peritoneal fluids), cerebrospinal fluid(CSF), bone marrow aspirates, and blood. Blood andstool specimens are usually cultured from AIDS patients.These specimens reveal numerous mycobacteria wheninfection is present in these patients. Wound or skinlesions (abscesses) require a technique using aspirationof the specimen into a syringe rather than the use of aswab to obtain the specimen.

Specimens not suitable for culture and usuallyrejected are 24-hour urine specimens, pooled sputum,saliva, and swabs containing pulmonary secretions. Thehigh rate of contamination as well as the reduced rate ofmycobacteria recovery in these specimens renders themunsuitable.

Specimen processing

Decontamination and digestion of sputum speci-mens is necessary to recover mycobacteria for cultureand identification. The process of decontamination(removing unwanted bacteria) and digestion (breakingdown mucous and protein) of sputum specimens is nec-essary to release the mycobacteria that may be presentbut are trapped in the mucous, and also to kill theunwanted bacteria (normal flora). Specimens from ster-ile body sites (blood, tissue, and body fluids, etc.) do notneed the process of decontamination and digestion as dosputum samples. If the process of decontamination anddigestion is not done or done improperly, recovery ofmycobacteria from sputum samples is inhibited causinga false-negative report. Mucous, cells, and normal bacte-rial flora (from the oral cavity) entrap and enmesh the

mycobacteria in sputum. A common decontaminant issodium hydroxide (4%) which is also used as a mucolyt-ic agent (for liquifaction or digestion of mucous). Acombination is often used which consists of N-acetyl-L-cysteine (NALC) and a lower concentration (2%) ofsodium hydroxide. This combination gives a betterrecovery rate when used together as a mucolytic-decont-aminant. Liquifaction of the thick mucous in sputum isnecessary to free the mycobateria trapped in it withoutharming the mycobacteria, and decontamination kills thenormal flora (bacteria from the mouth, throat and oralcavity) which interfere with the recovery of mycobacte-ria. The final product is reduced (concentrated) from theoriginal 5-10 mL volume, and a portion of the resultingspecimen is transferred by sterile technique to either ster-ile solid, tube or plate media, and liquid media, whileanother portion is used to make several smears on glassslides for staining.

Acid fast and fluorescent staining

The smears made after the process of decontamina-tion and digestion of sputum are stained using either anacid-fast staining procedure or a fluorochrome stain.Mycobacteria do not stain well with the Gram stainingprocedure used routinely in the microbiology laboratory.Specimens obtained from sterile sites (bone marrow, tis-sue, etc.) do not need processing and smears are madedirectly from the specimen onto glass microscopeslides. Mycobacteria are slightly curved or straight bacil-li, about 0.2 to 0.6 by 1.0 to 10 micrometers in size. Thecell wall of mycobacteria contains a high lipid content,and is made up of long-chain, multiply cross-linked fattyacids (mycolic acids). In the acid-fast staining procedure,a basic dye, carbolfuchsin stain, is used to stain the cellwall. The long-chain mycolic acids and waxes in themycbacteria cell wall serve to complex the carbol-fuchsin. The Ziehl-Neelsen acid fast stain for mycobac-teria uses heat to fix the dye in the cell wall, while theKinyoun staining method uses an increased concentra-tion of basic fuchsin and phenol eliminating the heatrequirement. In the Ziehl-Neelsen procedure, the carbol-fuchsin stain is left on the smear for five minutes whileheat is applied under the slide by a bunsen burner or a hotplate. The carbolfuchsin dye penetrates the cell wall andthe excess stain is washed off with a 3% acid-alcoholmixture (95% ethanol and 3% hydrochloric acid). Themycobacteria cell wall retains the dye (a red-purplecolor) and will not be decolorized (washed out) by theacid-alcohol, thus the term acid-fast. A second dye,methylene blue, is used to stain any background materi-al including any other bacteria that may be present. Thisdye results in a light background providing good contrastto the red-purple stain of the carbolfuchsin dye, thus aid-

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ing in the detection of acid-fast bacilli. If mycobacteriaare present in the smear, the appearance of red-purpleshort or long bacilli are observed at 1000 X magnifica-tion. Some species of mycobacteria appear “beaded”while others may appear pleomorphic (a mixture of coc-coid and rod shapes), or filamentous (branching of thebacillus).

Another staining method used for the detection ofmycobacteria is the auramine-rhodamine fluorochromestain. This method requires a fluorescent microscope.Smears are scanned at a lower magnification (250 X to400 X). The fluorochrome dyes used in this procedurecomplex to the mycolic acids in acid-fast cell walls. Thefluorescing mycobacteria are seen as bright yellow-orange bacilli against a dark background. Fluorescentstained smears can be read more rapidly than acid-faststains, but there are drawbacks. Mycobacteria spp. thatare rapid-growers may not appear fluorescent with thesestains; artifacts may fluoresce; material on the oil objec-tive may have floated off a previous positive smear caus-ing a false-positive reading for the next smear examined.All positive smears from the auramine-rhodamine fluo-rochrome method should be confirmed using the Ziehl-Neelsen method for acid-fast bacilli.

Acid-fast bacillus (AFB) smear report

Laboratories performing staining procedures andreporting smear results must adhere to guidelines fromthe U.S. Department of Health and Human Services(Public Health Service, Centers for Disease Control,Atlanta). The rule for reporting acid-fast smears formycobacteria requires scanning the smear for a mini-mum of 15 minutes (at least 300 oil immersion fields)before calling the slide negative for acid-fast bacilli or“No AFB seen.” The following are recommended inter-pretations and ways to report smear results:

• A request for another specimen or a doubtful report isthe result of seeing AFB of 1-2/300 fields for the Ziehl-Neelsen (Z-N) stain and AFB of 1-2/70 fields for theauramine-rhodamine (fluorochrome) stain.

• A “1+” report for AFB seen = 1-9/100 fields for the Z-N method and 2-18/50 fields for the fluorochromestain.

• A “2+” report for AFB seen = 1-9/10 fields for the Z-Nmethod and 4-36/10 fields for the fluorochrome stain.

• A “3+” report for AFB seen = 1-9/field for the Z-Nmethod and 4-36/field for the fluorochrome stain.

• A “4+” report for AFB seen = less than 9/field for theZ-N method and less than 36/field for the fluorochromestain.

Culture media and isolation methods

Several types of media are used for the cultivation ofmycobacteria, and each facility determines which onesare most appropriate for use. A combination of culturemedia is often used to optimize recovery of mycobacteriaas well as inhibit the growth of contaminants. Mycobac-teria require a pH of 6.5-6.8 for growth and grow best athigher humidity. Commercially prepared solid culturemedia (in tubes with screw-top caps) consist of bovineserum albumin agar-based media (Middle-brook 7H10and 7H11) and egg-based media (Lowenstein-Jensen).Liquid media (Middlebrook 7H9) is used to subculturestock strains or as part of a system (e.g., BACTEC 12Bmedium, Septi-Chek AFB) to cultivate and detect growthof acid-fast bacilli. Mycobacterium spp. grow more rapid-ly in liquid media; solid media takes approximately 17days for the isolation of acid-fast bacilli whereas liquidmedia takes only about 10 days. The following aredescriptions of three general types of media that are mostoften used.

• Lowenstein-Jensen media (L-J) is an egg-potato basesolid media containing malachite green (an inhibitoryagent). The use of L-J media is excellent for the recov-ery of M. tuberculosis from sterile-site specimens aswell as decontaminated-digested sputum specimens.

• Petragnani media is an egg-milk-potato solid mediumalso containing malachite green. It is primarily used forspecimens from highly contaminated areas (e.g., fecalmaterial).

• Middlebrook 7H10 media is a liquid based media con-taining salts, vitamins, cofactors, oleic acid, albumin,catalase, glycerol, and glucose. This media enhancesthe recovery of MAC organisms (Mycobacteria aviumcomplex).

Each culture medium described above represents anonselective formulation, but selective formulations arealso used which contain antibiotics to enhance the growthof mycobacteria and suppress the growth of contaminat-ing bacteria. The enhanced formulas are used for speci-mens that are highly contaminated.

All culture tubes are incubated in an atmosphere of5-10% CO2 (for growth enhancement) even thoughmycobacteria are strict aerobes. The tubed media are keptin a high humidity incubator at 35°C in the dark in aslanted

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