Equine Anesthesia. Monitoring and Emergency Therapy

481 Pages·2008·37.618 MB·English

by  William W. Muir, DVM, MSc, PhD, DACVA, DACVECC, and John A.E. Hubbell, DVM, MS, DACVA (Eds.)

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EQUINE ANESTHESIA: MONITORING AND EMERGENCY THERAPY, ISBN: 978-1-4160-2326-5
SECOND EDITION
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Copyright © 1991 by Mosby, Inc., an affiliate of Elsevier Inc.
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Notice
Knowledge and best practice in this field are constantly changing. As new research and experience broaden
our knowledge, changes in practice, treatment and drug therapy may become necessary or appropriate.
Readers are advised to check the most current information provided (i) on procedures featured or (ii) by the
manufacturer of each product to be administered, to verify the recommended dose or formula, the method
and duration of administration, and contraindications. It is the responsibility of the practitioner, relying on
their own experience and knowledge of the patient, to make diagnoses, to determine dosages and the best
treatment for each individual patient, and to take all appropriate safety precautions. To the fullest extent of
the law, neither the Publisher nor the Authors assumes any liability for any injury and/or damage to persons
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Library of Congress Cataloging-in-Publication Data
Equine anesthesia : monitoring and emergency therapy / [edited by]
William W. Muir, John A. E. Hubbell.—2nd ed.
p. ; cm.
Includes bibliographical references and index.
ISBN 978-1-4160-2326-5 (hardcover : alk. paper)
1. Horses—Surgery. 2. Veterinary anesthesia. I. Muir, William,
1946- II. Hubbell, John A. E.
[DNLM: 1. Anesthesia—veterinary. 2. Horses—surgery. SF 951
M9455e 2009]
SF951.E54 2009
636.1’089796—dc22
2008042056
Vice President and Publisher: Linda Duncan
Senior Acquisitions Editor: Anthony Winkel
Developmental Editor: Maureen Slaten
Publishing Services Manager: Patricia Joiner-Myers
Senior Project Manager: Joy Moore
Design Direction: Mark Oberkrom
Printed in the United States of America
Last digit is the print number: 9 8 7 6 5 4 3 2
Contributors
Richard M. Bednarski, DVM, MS, DACVA Phillip Lerche, BVSc, DAVCA
Associate Professor Assistant Professor – Clinical
Department of Veterinary Clinical Sciences Department of Veterinary Clinical Sciences
College of Veterinary Medicine The Ohio State University
The Ohio State University Columbus, Ohio
Columbus, Ohio Perioperative Pain Management
Tracheal and Nasal Intubation
Anesthetic Equipment Nora S. Matthews, DVM, DACVA
Professor and Co-Chief of Surgical Sciences
Lori A. Bidwell, DVM, DACVA Department of Small Animal Clinical Sciences
Head of Anesthesia College of Veterinary Medicine & Biomedical Sciences
Rood & Riddle Equine Hospital Texas A&M University
Lexington, Kentucky College Station, Texas
Anesthetic Risk and Euthanasia Anesthesia and Analgesia for Donkeys and Mules
John D. Bonagura, DVM, MS, DACVIM Wayne N. McDonell, DVM, MSc, PhD, DACVA
(Cardiology, Internal Medicine) Professor Emeritus, Anesthesiology
Professor and Head of Clinical Cardiology Services Department of Clinical Studies
Member, Davis Heart & Lung Research Institute Ontario Veterinary College
Department of Veterinary Clinical Sciences University of Guelph
College of Veterinary Medicine Guelph, Ontario, Canada
The Ohio State University Oxygen Supplementation and Ventilatory Support
Columbus, Ohio
The Cardiovascular System William W. Muir, DVM, MSc, PhD, DACVA,
DACVECC
Joanne Hardy, DVM, MSc, PhD, DACVS, DACVECC Regional Director, American Academy
Clinical Associate Professor of Surgery of Pain Management
Department of Large Animal Clinical Sciences Veterinary Clinical Pharmacology Consulting Services
College of Veterinary Medicine & Biomedical Sciences Columbus, Ohio
Texas A&M University History of Equine Anesthesia
College Station, Texas The Cardiovascular System
Venous and Arterial Catheterization and Fluid Therapy Physical Restraint
Monitoring Anesthesia
John A.E. Hubbell, DVM, MS, DACVA Principles of Drug Disposition and Drug Interaction
Professor of Anesthesia in Horses
Department of Veterinary Clinical Science Anxiolytics, Nonopioid Sedative-Analgesics, and Opioid
College of Veterinary Medicine Analgesics
The Ohio State University Local Anesthetic Drugs and Techniques
Columbus, Ohio Intravenous Anesthetic Drugs
History of Equine Anesthesia Intravenous Anesthetic and Analgesic Adjuncts to
Monitoring Anesthesia Inhalation Anesthesia
Local Anesthetic Drugs and Techniques Peripheral Muscle Relaxants
Peripheral Muscle Relaxants Perioperative Pain Management
Considerations for Induction, Maintenance, and Recovery Considerations for Induction, Maintenance, and Recovery
Anesthetic-Associated Complications Anesthetic-Associated Complications
Cardiopulmonary Resuscitation Cardiopulmonary Resuscitation
Anesthetic Protocols and Techniques for Specific Procedures Anesthetic Protocols and Techniques for Specific
Anesthetic Risk and Euthanasia Procedures
Anesthetic Risk and Euthanasia
Carolyn L. Kerr, DVM, DVSc, PhD, DACVA
Associate Professor of Anesthesiology James T. Robertson, DVM, DACVS
Department of Clinical Studies Equine Surgical Consultant
Ontario Veterinary College Woodland Run Equine Veterinary Facility
University of Guelph Grove City, Ohio
Guelph, Ontario, Canada Physical Restraint
Oxygen Supplementation and Ventilatory Support Preoperative Evaluation: General Considerations
v
vi Contributors
N. Edward Robinson, BVetMed, MRCVS, PhD Eugene P. Steffey, VMD, PhD, DACVA
Honorary Diplomate, ACVIM Professor Emeritus
Matilda R. Wilson Professor Department of Surgical and Radiological Sciences;
Department of Large Animal Clinical Sciences Pharmacologist
College of Veterinary Medicine K.L. Maddy Equine Analytical Chemistry Laboratory
Michigan State University California Animal Health and Food Safety Laboratory
East Lansing, Michigan University of California, Davis
The Respiratory System Davis, California
Inhalation Anesthetics and Gases
Richard A. Sams, PhD
Professor and Program Director Ann E. Wagner, DVM, MS, DACVA, DACVP
Florida Racing Laboratory Professor, Anesthesia
College of Veterinary Medicine Department of Clinical Sciences
University of Florida College of Veterinary Medicine & Biomedical Sciences
Gainesville, Florida Colorado State University
Principles of Drug Disposition and Fort Collins, Colorado
Drug Interaction in Horses Stress Associated with Anesthesia and Surgery
Colin C. Schwarzwald, Dr.med.vet., PhD, DACVIM Kazuto Yamashita, DVM, PhD
Assistant Professor Professor
Section of Internal Medicine Department of Small Animal Clinical Sciences
Equine Department School of Veterinary Medicine
Vetsuisse Faculty of the University of Zurich Rakuno Gakuen University
Zurich, Switzerland Ebetsu, Hokkaido, Japan
The Cardiovascular System Intravenous Anesthetic and Analgesic Adjuncts to Inhalation
Anesthesia
Claire Scicluna, DVM
Clinique Vétérinaire du Plessis
Chamant, France
Preoperative Evaluation: General Considerations
Roman T. Skarda, DVM, PhD, DACVA (Deceased)
Professor
Department of Veterinary Clinical Sciences
College of Veterinary Medicine
The Ohio State University
Columbus, Ohio
Local Anesthetic Drugs and Techniques
Dedication
This edition is dedicated to our friend, the late Dr. Roman ature, book chapters, and teaching materials contributed
T. Skarda. Romi Skarda was a colleague and friend for immeasurably to the advancement of equine medicine and
over 30 years. A Diplomate of the American College of surgery. A consummate entertainer, magician, and always
Veterinary Anesthesiologists, Romi was recognized as the the life of any party, Romi will be remembered as the most
world’s expert on local and regional anesthesia of animals, compassionate, gentlest, and strongest man either one of
especially horses. His contributions to the scientific liter- us has known.
vii
Preface
The first edition of this book, published in 1991, was writ- recovery from anesthesia. Surely we can do better. The cardio-
ten “to provide the specialist interested in equine surgery and pulmonary effects of all current anesthetic drugs have been
anesthesia, the veterinary surgeon, technical support staff, determined, and dependable monitoring techniques have
and veterinary students with a thorough and in-depth dis- evolved and been investigated in horses. In our experience
cussion of equine anesthesiology.” The preface to that edition there are few complications that are “new”; and most compli-
noted that the evolution of the practice of equine anesthesia cations, if discovered promptly, can be averted. Another one
had been slow but that the incidence of postoperative myo- third of anesthetic-associated deaths in horses are attributed
pathy had dropped dramatically because of the adoption of to fractures or myopathy in the postoperative period. The goal
improved monitoring techniques and methods for cardio- of recovery from anesthesia should be the calm, coordinated
pulmonary support, including the use of vasopressors and resumption of a standing posture on the first attempt within
mechanical ventilation. Much has been learned from the writ- a time frame that does not exacerbate the consequences of
ings and research of those interested in equine anesthesia (see recumbency. Multiple methods have been proposed to attain
Chapter 1; “Those who don’t know history are destined to this goal, but none has emerged as universally acceptable.
repeat it.” Edmund Burke) and the 17 years that have passed Clearly the horse is unique among the commonly
since the first publication of this text. Most of the original anesthetized domestic species, and some level of stress
contributors have agreed to rewrite, update, and expand their accompanies every anesthesia. Procedures designed to
original contributions to further define the art and science of reduce pain and stress and improve the horse’s quality of
equine anesthesia. New chapters on pain management; anes- life throughout the anesthetic experience require greater
thetic adjuncts; and techniques for induction, maintenance, focus. Toward this end the education of all involved in the
and recovery from anesthesia focus on areas of increased con- practice of equine anesthesia cannot be overemphasized.
cern and a need for improvement. They provide a relatively Furthermore, the employment of educated, trained, expe-
succinct presentation of what is known and offer suggestions rienced, and ultimately certified personnel should be a
for future direction. A new chapter on anesthesia of donkeys prerequisite to the practice of equine anesthesia. The first
and mules broadens the text to include other members of the edition of this text was dedicated to two pioneers in equine
genus Equus encountered by the equine veterinarian. surgery and anesthesia: Drs. Albert Gabel and Robert
Anesthetic risk in horses is greater than that in dogs, cats, Copelan. They epitomize the foundation upon which the
or humans. Mortality data suggest that the risk of death science and art of equine practice was built: Dr. Gabel’s
from anesthesia in otherwise normal horses ranges from passion and inquisitiveness and Dr. Copelan’s persistence
0.1% to 1%. Factors known to contribute to this risk include (still practicing at 82 years of age) and emphasis on perfec-
youth or old age; longer durations of anesthesia; stress; tion. In addition, we recognize Dr. Peter Rossdale whose
and emergency procedures, particularly colic. Anesthetic dedicated service as chief editor of the Equine Veterinary
risk is greater at night than during the day, but even the Journal has become synonymous with a persistence for
simplest anesthetic procedure in horses carries an increased excellence in equine veterinary science. The future for
risk of complications. At least one third of the deaths equine anesthesia is clear and will be enhanced by the
associated with equine anesthesia have been attributed to car- attributes of passion, perseverance, persistence, and pur-
diac arrest. It is important to note that approximately 25% suit of excellence and realized by the efforts of dedicated,
of all horses that die do so from injuries occurring during vigilant equine anesthetists.
William W. Muir John A.E. Hubbell
ix
Acknowledgments
We would like to extend our sincerest thanks to the past and Dr. Tokiko Kushiro
current veterinary technicians, interns, residents, and fac- Dr. Deborah Grosenbaugh
ulty members of the Equine Medicine and Surgery Section Dr. Lindsay Culp
of the Department of Veterinary Clinical Sciences at The Dr. Juliana Figueiredo
Ohio State University. Special recognition to: Dr. Turi Aarnes
Anesthesia Technical Support and Advice Graphics, Illustrations, and Photographs
Amanda English Marc Hardman
Carl O’Brien Jerry Harvey
Renee Calvin Tim Vojt
Deana Vonschantz (New England Equine, Dover, NH)
Library and Editorial Assistance and Typing
Barbara Lang
Review, Critique, Editing
Dr. Jay Harrington
Dr. Anja Waselau
Susan Kelley
Dr. Martin Waselau
Robin Bennett
Dr. Ashley Wiese
Dr. Yukie Ueyama
xi
1
History of Equine Anesthesia
William W. Muir
John A.E. Hubbell
In comparison with the ancients, we stand like dwarfs on the destitute because of attempts to patent his new invention.
shoulders of giants. This paradigm shift (crystallization of thought) fostered the
Bernard of Chartres secularization of pain, and a moral transformation that nei-
ther humans nor animals should be subjected to or allowed
Those who don’t know history are destined to repeat it. to suffer pain.
The word anesthesia became synonymous with uncon-
edmund Burke sciousness that provided insensibility to pain, a viewpoint
that persisted for the next 50 years. As the clinical use of
Reports that say that something hasn’t happened are always
neuromuscular blocking drugs, opioids, barbiturates, and
interesting to me, because as we know, there are known knowns;
diethyl ether became more commonplace, the term was
there are things we know we know. We also know there are known
redefined in 1957 by Woodbridge to include four specific
unknowns; that is to say we know there are some things we do not
components: sensory blockade (analgesia); motor blockade
know. But there are also unknown unknowns — the ones we don’t
(muscle relaxation); loss of consciousness or mental block-
know we don’t know. And if one looks throughout the history of
ade (unconsciousness); and blockade of undesirable reflexes of
our country and other free countries, it is the latter category that
the respiratory, cardiovascular, and gastrointestinal systems.4
tend be the difficult ones.
Woodbridge believed a single drug or a combination of drugs
donald h. rumsfeld could be used to achieve the different components of anes-
(feB. 12, 2002, department of defense news Briefing) thesia, a concept that led to the development of drug combi-
nations to produce a state of “balanced anesthesia.” Various
prominent anesthesiologists have proposed alternative defini-
Defining AnesthesiA in equine tions. Prys-Roberts (1987)5 suggested that anesthesia should
PrActice: An emerging science be considered “drug-induced unconsciousness…the patient nei-
ther perceives nor recalls noxious stimulation”; Pinsker (1986)6
Equine anesthesia is a species-specific art and science proposed “paralysis, unconsciousness, and the attenuation of
(Table 1-1). The word anesthesia was first defined in Bailey’s the stress response”; and Eger (1993)7 “discussed reversible
English Dictionary in 1751 as “a defect in sensation.” oblivion and immobility.” Interestingly, a recent edition (27th)
Historically the word anesthesia has held special significance of Stedman’s Medical Dictionary (2005) provides the follow-
because it is associated with the public demonstration of sur- ing definition—“1. Loss of a sensation resulting from phar-
gical anesthesia in humans by William Morton in America macological depression of nerve function or from neurological
in October 1846.1,2 This single dramatic and widely publi- dysfunction. 2. Broad term for anesthesiology as a clinical spe-
cized event in the wake of earlier unpublicized successes cialty”— that is not as descriptive as Woodbridge’s, although
(Crawford Long used ether to remove a tumor from the multiple qualifiers have been added (e.g., local, regional, gen-
neck of a patient on March 30, 1842) established the idea eral, surgical, dissociative (Figure 1-1).
that drugs could and should be administered to render Given recent advances in our current understand-
patients free from surgical pain. Bigelow1 states, “No single ing of the pharmacodynamics (drug concentration-effect)
announcement ever created so great and general excitement of anesthetic drugs in horses and the differing anesthetic
in so short a time. Surgeons, sufferers, scientific men, every- requirements for surgery (e.g., orthopedic; abdominal),
body, united in simultaneous demonstration of heartfelt mutual any definition of anesthesia should include any and all
congratulation (pp 175-212).” Most important, Morton’s effects that protect the patient from the trauma of surgery
demonstration heralded a true paradigm shift, as defined by or produce desirable supplements to anesthesia, includ-
T.S. Kuhn,3 in that it represented an unprecedented crystalli- ing treatments that provide analgesia long after the admin-
zation of thought of sufficient magnitude to attract an endur- istration of anesthetic drugs.8 This viewpoint continues
ing group of adherents while being open-ended enough to to gain acceptance, as evidenced by detailed manuscripts
serve as a new direction and model for future research. This in the Equine Veterinary Journal, the American Journal of
crystallization of thought was made possible by the efforts of Veterinary Research, and the Journal of Veterinary Anesthesia
a dedicated scientific community, including Sir Humphrey and Analgesia describing the anxioltic, hypnotic, analge-
Davy, Michael Faraday, Henry Hill Hickman, Crawford Long, sic, and muscle relaxant effects of α-a drenoceptor ago-
2
Horace Wells, J.Y. Simpson, J. Priestley, John Snow (1813- nists/dissociative anesthetic/centrally acting muscle relaxant
1856; heralded as the first anesthesiologist), and others.3 drug combinations (e.g., detomidine/ ketamine/guaifenesin)
However, like a typical character in George Orwell’s 1984, for total intravenous anesthesia (TIVA); the use of inhal-
Morton (as many other practitioners of anesthesia) was “the ant anesthetics (e.g., isoflurane, sevoflurane, desflurane)
victim of history rewritten by the powers that be,” dying almost in combination with various intraoperative anesthetic adjuncts
1
2 chapter 1  n History of Equine Anesthesia
table 1–1. Historical events important in equine anesthesia
time period historical event
Before 1500s (Herbalism) Plant extracts produced: atropine, opium, cannabis
1500-1700 (Emerging) Anesthesia defined as “a defect in sensation”
Ether (1540)
Needles (intravenous access)
1800s (Developing) Anesthesia comes of age: William Morton (1846) demonstrates ether anesthesia in
America: “Gentlemen, this is no humbug.”
Key drug developments:
• Peripheral muscle relaxants: curare (1814)
• Inhalant anesthetics: carbon dioxide (1824), nitrous oxide (N O, 1844), chloroform
2
(1845), ether (Mayhew, 1847)
• Intravenous: chloral hydrate (Humbert, 1875)
• Local anesthetic: cocaine (1885)
• Equipment: face masks, orotracheal tubes, inhalant anesthetic apparatus
• Anesthetic record keeping
1900-1950 (Achieving) Key drug developments:
• Chloral hydrate (combinations with magnesium sulfate, pentobarbital)
• Barbiturates (pentobarbital, thiopental)
• Local anesthetic drugs and techniques developed (procaine)
• Peripheral muscle relaxants (succinyl choline)
• Compulsory Anesthetic Use Act in the UK (1919)
Key texts:
• E. Stanton Muir, Materia Medica and Pharmacy (1904)
n  Atropine, cannabis, humulus, herbane, chloral, cocaine, codeine, morphine,
narcotina, heroin, ethyl alcohol, chloroform, ether
• L.A. Merillat, Principles of Veterinary Surgery (1906)
n  First American surgeon to devote dedicated attention to anesthesia
• Sir Frederick Hobday, Anesthesia and Narcosis of Animals and Birds (1915)
n  First English text on veterinary anesthesia: introduces concepts of preanesthetic
medication; pain relief; and local, regional, and spinal anesthesia
• J.G. Wright, Veterinary Anaesthesia (1942; ed 2, 1947)
n  Cannabis, chloral hydrate, pentobarbital, thiopental, chloroform, ether, morphine,
bulbocapnine
• E.R. Frank, Veterinary Surgery Notes (1947)
n  Chloral hydrate and magnesium sulfate, pentobarbital, procaine
1950-2000 (Extending) Art becomes a science
Controlled studies conducted on horses
Key drug developments:
• Central muscle relaxants (e.g., guaifenesin, diazepam)
• Peripheral muscle relaxants (e.g., atracurium)
• Phenothiazines (e.g., promazine, acepromazine)
• α -Agonists (e.g., xylazine, detomidine, medetomidine, romifidine)
2
• Dissociative anesthetics (e.g., ketamine, tiletamine)
• Hypnotics (e.g., propofol)
• Inhalants (e.g., cyclopropane, methoxyflurane, halothane, isoflurane, enflurane,
sevoflurane, desflurane)
Species-specific anesthetic equipment and ventilators
Monitoring techniques and equipment
Key texts:
• J.G. Wright, Veterinary Anaesthesia, (ed 3, 1952; ed 4, 1957)
• J.G. Wright, L.W. Hall, Veterinary Anaesthesia and Analgesia, ed 5 (1961)
n  Subsequent editions by L.W. Hall and K.W. Clarke
• L.R. Soma, Textbook of Veterinary Anaesthesia (1971)
n  Chapter 23, written by L.W. Hall, describes anesthesia in horses
• W.V. Lumb, E. Wynn Jones, Veterinary Anaesthesia (1973)
• C.E. Short, Principles and Practice of Veterinary Anesthesia (1987)
n  Chapter 13, Part 1: “Special considerations of equine anesthesia”
n  Chapter 13, Part 8: “Anesthetic considerations in the conditioned animal”
• W.W. Muir, J.A.E. Hubbell, Equine Anesthesia: Monitoring and Emergency Therapy (1991)
n  First text on anesthesia completely devoted to the horse
(Continued)
chapter 1  n History of Equine Anesthesia 3
table 1–1. Historical events important in equine anesthesia —Cont’d
time period historical event
1950-2000 Extending (Cont’d) Detailed anesthetic records
Species-specific designed anesthetic equipment and ventilators
Monitoring techniques and equipment
“Point of care” blood chemistry (e.g., pH, PO , PCO ) equipment
2 2
Anesthesia universally taught as part of veterinary school curriculum
American (1975) and European (1993) colleges established
Information transfer (computer networks and assisted learning)
2000-present Refinement in equine anesthetic equipment
Development of computerized ventilators and respiratory monitoring equipment
Holothane discontinued in the United States; replaced by isoflurane and sevoflurane
Deflurane investigated for clinical use in horses
Advanced monitoring techniques, including telemetry and minimally invasive methods for
the determination of cardiac output, used at veterinary teaching hospitals
Key texts:
• T. Doherty, A. Valverde, eds, Manual of Equine Anesthesia and Analgesia (2006)
• P.M. Taylor, K.W. Clarke, Handbook of Equine Anesthesia, ed 2 (2007)
Anesthesia
Local anesthesia Regional anesthesia General anesthesia
Topical Infiltration Peripheral Total inhalation Balanced Total
nerve block anesthesia anesthesia intravenous
anesthesia
(TIVA)
Epidural
Inhalant
anesthesia
Spinal
Injectable
anesthesia
Intravenous
Anesthetic
regional
adjuncts
Figure 1–1. Types of anesthetic procedures.
(e.g., ketamine, lidocaine, medetomidine, morphine); and
the administration and infusion of analgesic drugs before, Unconsciousness, Cardiovascular
anxiolysis instability
during, and after the anesthetic event. The “ideal” anes-
Hypnosis
thetic state (e.g., sedation, analgesia, muscle relaxation, loss
of consciousness) in horses is best achieved by administer- + -
ing multiple drugs in combination or sequence to produce Immobility Hypoventilation,
the desired effects on consciousness and pain. The advan- Relaxation + - hypoxia
tages of this “multimodal” approach include, but are not General
limited to, an increase in the potential for additive or syn- Anesthesia
Suppression of
ergistic beneficial anesthetic effects, an increase in the scope responses to + - Excitation,
of anesthetic activity (e.g., analgesia and muscle relaxation), noxious stimuli delirium
and the potential to reduce side effects or an adverse event. Analgesia + -
The disadvantages include the potential for adverse drug
Suppression Shivering,
interactions, resulting in a greater potential for side effects
of 'Stress' etc.
(e.g., bradycardia, ileus, ataxia), adverse events (e.g., hypo-
response
tension, respiratory depression), and prolonged recovery
from anesthesia. It is mandatory that the equine anesthe-
tist become knowledgeable and proficient in administrat-
Figure 1–2. The key components of anesthesia include loss of con-
ing a select group of drugs that provide the aforementioned
sciousness (hypnosis), analgesia, muscle relaxation, and suppression of
anesthetic qualities if the “best” outcome is to be achieved
stress. Drugs that produce anxiolysis and reduce stress are frequently
(Figure 1-2). administered as preanesthetic medication.
4 chapter 1  n History of Equine Anesthesia
the evolution of equine AnesthesiA action of the vapor on the horse; but I cannot anticipate that
it will be found of service to that animal…. We should be cau-
The practice of anesthesia evolved from an art to a science tious lest we become cruel under the mistaken endeavour to be
during the 1800s.9 H.H. Hickman administered carbon kind.” Others of this era were more optimistic than Mayhew.
dioxide to animals in 1824 to render them unconscious.10–13 Percivall, a graduate physician and veterinarian, stated in
However, before 1850 (and for a long time thereafter), the that same year, “We must confess we augur more favourably
practice of equine anesthesia remained an art overly depen- of the inferences deducible from them [Mayhew’s experiments]
dent on herbal remedies (Atropa mandragora, opium, hen- than he would seem to. To us it appears questionable whether
bane, hemlock) and physical restraint (“a heavy hand”).12,13 the cries emitted by the animals during experiments are to be
The practical advantages of anesthesia and its potential regarded as evidence of pain.”12,13
benefits for equine surgery were advocated by G.H. Dadd Within 1 year of Morton’s demonstration, “ether mania”
1 year after Morton’s demonstration (1847) and recorded had reached its peak, only to subside primarily because of
in his book Modern Horse Doctor (1854).12,13 It is apparent Simpson’s (1847) demonstration of the advantages of chlo-
from these writings that the medical care of horses was, for roform compared to ether: “1st. A much less quantity will
the most part, left to untrained individuals. Books such as produce the same effect. 2nd. A more rapid, complete and gen-
Edward Mayhew’s The Illustrated Horse Doctor, published in erally more persistent action, with less preliminary excitement
1880,14 were written to “render the gentleman who had con- and tendency to exhilaration and talking. 3rd. The inhalation
sulted it independent of his groom’s dictation;…enable any per- is far more agreeable and pleasant than that of ether. 4th.
son who had read it capable of talking to a veterinary surgeon As a smaller quantity is used, the application is less expen-
without displaying either total ignorance or pitiable prejudice; sive, which becomes an important consideration if brought into
and which, in cases of emergency, might direct the uninitiated general use. 5th. The perfume is not unpleasant, but the reverse,
in the primary measures necessary to arrest the progress of the and more evanescent. 6th. No particular instrumental inhaler
disease; and…might even instruct the novice in such a man- is necessary.”1 However, skepticism, pragmatism, and reluc-
ner as would afford a reasonable prospect of success.” Such tance to change were the order of the day, with comments
texts covered all of the known maladies of the day, including from equine surgeons warning (Box 1-1), “It is, in my opin-
simple ophthalmia, staggers, gutta serena, nasal gleet, and ion, very doubtful whether chloroform will ever become an
scald mouth. Most surgeries were performed with physical efficient agent in veterinary practice on the horse, as I believe
restraint of the horse rather than anesthesia (Figure 1-3). these two bad-conditioned animals [neurotomy surgeries in two
Directions for casting the horse included statements such horses] suffered more in being reduced to a state of insensibility,
as: “Let it be hobbled and never, during the operation, hear any and in recovering from the state, than they did from the opera-
sound but soothing accents. Animals do not understand words, tion performed”; and “We very often delude ourselves in regard
creatures may not be able to literally interpret; but they com- to the operation of medicines, which seldom effect what we sup-
prehend all that the manner conveys.” Mayhew may have been pose them to do. For this reason it is proper that we should be
the first individual to use diethyl ether in horses, although sceptical with regard to new remedies, which hardly ever main-
similar experiments in animals, including horses, were tain the character bestowed upon them by their first employ-
reported in France, Germany, Russia, and the United States. ers.” An editorial in the Veterinarian in 1848 suggested,
Mayhew’s experiences (1847) caused him to comment with “abandoning the use of this potent chemical [chloroform] agent
skepticism, “The results of these trials are not calculated to as an anesthetic, at least for practical purposes, [instead] let
inspire any very sanguine hopes. We cannot tell whether the us turn our attention to it as an internal remedy”; and other
cries emitted are evidence of pain or not but they are sugges- writings suggested that ether and chloroform be reserved
tive of agony to the listener, and, without testimony to the con- for internal use (as vermicides) and that during the 1850s
trary, must be regarded as indicative of suffering…. There has “Horses continued to be bled and purged with vehemence, and
yet been no experiment that I know of made to ascertain the operated on without benefit of anesthesia.” However, these
A B
Figure 1–3. A and B, The use of hobbles, casting harnesses, and ropes were an essential part of equine
“anesthesia” until inhalants and dissociative anesthetics were introduced.