Feline Anesthesia and Pain Management E-Book
91,99 €
Mehr erfahren.
- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Feline Anesthesia and Pain Management offers a definitive and practical guide to feline anesthesia and pain management. * The only book offering detailed practical information on anesthesia and pain management in cats, one of the world's most popular pets * World renowned author team * Quick reference format with full color illustrations * Offers detailed practical information on anesthesia and pain management tailored to the unique needs of cats * Includes a team of world-renowned authors who are experts in veterinary anesthesia and analgesia * Uses a quick reference format that makes the information easy to find and follow * Presents full color images to illustrate concepts
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 533
Veröffentlichungsjahr: 2017
Ähnliche
Contents
Cover
Title Page
Copyright
Dedication
Foreword
Contributors
Chapter 1: Handling, Restraint, and Preanesthetic Assessment
Introduction
Handling and Restraint
Preanesthetic Assessment
Risk Factors, Morbidity, and Mortality
Further Reading
Chapter 2: Anatomy, Physiology, and Pharmacology
Introduction
Cardiovascular System
Respiratory System
Nervous System
Urinary System
Hepatic System
Endocrine System
Gastrointestinal System
Further Reading
Chapter 3: Sedation and Premedication
Introduction
Drugs used for Sedation in Cats
Acepromazine
Benzodiazepines
Agonists of α2-Adrenergic Receptors
Anticholinergics
Opioids
Ketamine and Alfaxalone
Trazodone
Other Drugs
Further Reading
Chapter 4: Injectable Anesthetics and Induction of Anesthesia
Introduction
General Considerations for Induction of Anesthesia
Drugs used for Induction of Anesthesia
Propofol
Alfaxalone
Dissociative Anesthetics (Ketamine and Tiletamine)
Barbiturates
Etomidate
Fentanyl plus Midazolam
Induction with Volatile Anesthetics
Total Intravenous Anesthesia (TIVA)
Infusion Devices
Injectable-only Protocols
Further Reading
Chapter 5: Local Anesthetics and Loco-regional Techniques
Introduction
Physicochemical and Pharmacodynamic Properties of Local Anesthetics
Axons and Nerve Fibers
Pharmacokinetics
Factors Influencing Onset and Duration of Action
Metabolism
Adjuvants
Local Anesthetics
Techniques for Nerve Location
Local Anesthetic Techniques
Further Reading
Chapter 6: Inhalation and Balanced Anesthesia
Volatile Anesthetics
Halothane
Isoflurane
Sevoflurane
Desflurane
Balanced Anesthetic Techniques
Opioids
Ketamine
Nitrous Oxide
Lidocaine
Dexmedetomidine
Gabapentin
Balanced Anesthesia Summary
Breathing Systems
Further Reading
Chapter 7: Monitoring
Introduction
Clinical Monitoring using Physical Senses (“Hands On”)
Cardiovascular System
Respiratory System
Further Reading
Chapter 8: Fluid Therapy
Introduction
Feline Physiology and Pathology with regard to Fluid Therapy
Fluids
Preoperative Preparation
Intraoperative Fluids
Postoperative Care
Further Reading
Chapter 9: Anesthetic Management of Special Conditions
Introduction
Urethral Obstruction and Uroabdomen
Chronic Kidney Disease (CKD)
Hyperthyroidism
Hypertrophic Cardiomyopathy (HCM)
Neuroanesthesia
Diaphragmatic Rupture
Gastrointestinal Emergencies
Idiopathic Hepatic Lipidosis
Diabetes Mellitus
Other Conditions
Further Reading
Chapter 10: Anesthetic Complications
Introduction
Airway Management
Respiratory Insufficiency
Circulation
Trauma
Recovery
Body Temperature
Cardiopulmonary Resuscitation (CPR)
Further Reading
Chapter 11: Mechanisms of Pain
Introduction
Mechanisms of Modulation in Tissues
Mechanisms of Modulation in Peripheral Nerves
Mechanisms of Modulation in The Spinal Cord
Mechanisms of Modulation in the Brain
The Role of Glial Cells (Glia, Neuroglia) and the Immune System
Mechanisms of Cancer Pain
Diabetic Neuropathy
Pruritus (Itch)
Further Reading
Chapter 12: Assessment and Recognition of Acute Pain
Introduction
Pain-assessment Tools
Behavior-based Indicators of Pain (Box 12.3)
Intervention Scores
Using Response to Treatment as a Diagnostic Tool
Confounding Factors
Personality, Fear and Stress
Using Pain-assessment Tools
Continued Assessment at Home
Further Reading
Chapter 13: Treatment of Acute (Adaptive) Pain
Introduction
Challenges in Feline Pain Management
Principles of Pain Management
Nonpharmacological Therapies in Acute Pain Management
Pharmacological Therapy in Acute Pain Management
Further Reading
Chapter 14: Assessment and Recognition of Chronic (Maladaptive) Pain
Introduction
Common Causes of Chronic Pain
Clinical Signs
Implications for Quality of Life
The Concept of Analgesic Challenge
Assessing Chronic Pain in Specific Conditions
Further Reading
Chapter 15: Treatment of Chronic (Maladaptive) Pain
Introduction
Client Communication: A Crucial Component of Treatment for Chronic Painful Conditions
Challenges in the Treatment of Chronic Pain in Cats
Pharmacological Therapy
Opioids
Local Anesthetics
Nonsteroidal Anti-inflammatory Drugs (NSAIDs)
Tramadol
Gabapentin
Amitriptyline
Amantadine
Emerging Analgesic Modalities
Other Analgesics
Nonpharmacological Treatment
Physical Activity and Weight Control
Physical Therapy, Massage, Acupuncture, and Transcutaneous Electrical Nerve Stimulation (TENS)
Monitoring for Treatment Efficacy
Degenerative Joint Disease (DJD)
Further Reading
Index
End User License Agreement
List of Tables
Table 1.1
Table 1.2
Table 1.3
Table 2.1
Table 2.2
Table 2.3
Table 2.4
Table 2.5
Table 3.1
Table 3.2
Table 4.1
Table 4.2
Table 5.1
Table 5.2
Table 5.3
Table 6.1
Table 7.1
Table 8.1
Table 8.2
Table 8.3
Table 11.1
Table 11.2
Table 11.3
Table 13.1
Table 14.1
Table 14.2
Table 15.1
Table 15.2
List of Illustrations
Figure 1.1
Figure 1.2
Figure 1.3
Figure 1.4
Figure 1.5
Figure 1.6
Figure 2.1
Figure 2.2
Figure 2.3
Figure 2.4
Figure 2.5
Figure 3.1
Figure 3.2
Figure 3.3
Figure 4.1
Figure 4.2
Figure 5.1
Figure 5.2
Figure 5.3
Figure 5.4
Figure 5.5
Figure 5.6
Figure 5.7
Figure 5.8
Figure 5.9
Figure 6.1
Figure 6.2
Figure 6.3
Figure 6.4
Figure 6.5
Figure 7.1
Figure 7.2
Figure 7.3
Figure 7.4
Figure 7.5
Figure 7.6
Figure 8.1
Figure 8.2
Figure 9.1
Figure 9.2
Figure 9.3
Figure 9.4
Figure 9.5
Figure 9.6
Figure 10.1
Figure 10.2
Figure 10.3
Figure 10.4
Figure 10.5
Figure 10.6
Figure 10.7
Figure 10.8
Figure 10.9
Figure 10.10
Figure 11.1
Figure 11.2
Figure 11.3
Figure 11.4
Figure 11.5
Figure 12.1
Figure 12.2
Figure 12.3
Figure 12.4
Figure 12.5
Figure 12.6
Figure 12.7
Figure 12.8
Figure 12.9
Figure 12.10
Figure 12.11
Figure 13.1
Figure 13.2
Figure 13.3
Figure 13.4
Figure 13.5
Figure 14.1
Figure 14.2
Figure 14.3
Figure 14.4
Figure 14.5
Figure 14.6
Figure 15.1
Figure 15.2
Figure 15.3
Figure 15.4
Figure 15.5
Guide
Cover
Table of Contents
Foreword
Chapter 1
Pages
i
ii
iii
iv
v
vi
xvii
xviii
xix
xx
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
Feline Anesthesia and Pain Management
Edited by
Paulo Steagall
Université de Montréal, Saint-Hyacinthe, Canada
Sheilah Robertson
Lap of Love Veterinary Hospice, Lutz, FL, United States
Polly Taylor
Taylor Monroe, Little Downham, Ely, United Kingdom
This edition first published 2018© 2018 John Wiley & Sons, Inc.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.
The right of Paulo Steagall, Sheilah Robertson, and Polly M Taylor to be identified as the editors of the editorial material in this work has been asserted in accordance with law.
Registered OfficeJohn Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA
Editorial Office111 River Street, Hoboken, NJ 07030, USA
For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com.
Wiley also publishes its books in a variety of electronic formats and by print-on-demand. Some content that appears in standard print versions of this book may not be available in other formats.
Limit of Liability/Disclaimer of Warranty
The contents of this work are intended to further general scientific research, understanding, and discussion only and are not intended and should not be relied upon as recommending or promoting scientific method, diagnosis, or treatment by physicians for any particular patient. In view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of medicines, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each medicine, equipment, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
Library of Congress Cataloging-in-Publication Data
Names: Steagall, Paulo V. M., author. | Robertson, Sheilah A., author. |Taylor, Polly M., author.
Title: Feline anesthesia and pain management / by Paulo V.M. Steagall, Sheilah A. Robertson, Polly Taylor.
Description: Hoboken, NJ : Wiley, 2018. | Includes bibliographical references and index. |
Identifiers: LCCN 2017026911 (print) | LCCN 2017027877 (ebook) | ISBN9781119167846 (pdf) | ISBN 9781119167877 (epub) | ISBN 9781119167808 (pbk.)
Subjects: | MESH: Cat Diseases–drug therapy | Pain Management–veterinary |Anesthesia–veterinary
Classification: LCC SF985 (ebook) | LCC SF985 .S74 2018 (print) | NLM SF 985| DDC 636.8/089796–dc23
LC record available at https://lccn.loc.gov/2017026911
Cover images: Courtesy of the editors
Cover design by Wiley
Dedication
Paulo SteagallTo my mother Ilza who has always supported my dreams. To my partner in crime Beatriz Monteiro who accepted me to ride along in this journey. To my father who taught me the love for cats. To Polly Taylor and Sheilah Robertson for believing. This book is for all cats and for people who dedicate their lives to protect and help them. Cats gave me a reason to become a veterinarian, and a job for the rest of my life.
Sheilah RobertsonTo my parents who always believed in education and supporting my career choice. To Paulo Steagall and Polly Taylor for their friendship, unwavering patience, and dedication to detail during the writing and editing process. To all the cats that have owned me and all my feline patients, thank you for everything you have taught me.
Polly TaylorThanks to Leslie Hall and Peter Lees who each in their own way encouraged me in the pursuit of all things feline – for cats in their own right, not as “little dogs.” To all cats, wonderful creatures, especially those who have owned me over the years, and particularly to Jasper, the current incumbent, who typed enthusiastically, if unhelpfully, some variations on the text herein. And most of all to Paulo and Sheilah for making it all happen, and to my family for their extreme patience and well-timed glasses of wine.
We would like to thank all collaborators for donating their time and expertise for this book.
Foreword
It gives me enormous pleasure, and it is a great privilege, to be able to write a preface for the first edition of this new book, edited and coauthored by Drs. Paulo Steagall, Sheilah Robertson, and Polly Taylor. If you are reading this having just purchased the book, the first thing to say is congratulations! You have made a sound investment!
For many decades there has been a trend for growth in cat ownership, and in many countries throughout the world the pet cat population now exceeds that of dogs. Despite their rising popularity, cats are still often a “second class” veterinary patient. Cats are taken to the veterinarian less frequently than dogs, and, regrettably, veterinary publications on dogs still far outweigh those on cats. Things are changing though – many practitioners appreciate the real value in focusing on the differing (and sometimes unique) needs of cats, and there is a growing emphasis on a better understanding of cats as veterinary patients.
The welfare of patients under our care is, of course, the primary concern of every veterinarian. It is also true that, in terms of animal welfare, nothing is more important than pain relief, which is why I am so pleased to see the publication of this new book. It is nearly 25 years since the last veterinary book to focus on feline anesthesia was published (Anaesthesia of the Cat, edited by Hall and Taylor, published in 1994). As so much has changed in our knowledge in the past 25 years, this new publication is both timely and a very welcome addition to the literature.
This book takes a very practical approach to feline anesthesia and analgesia. It is designed to be a practical clinical tool, providing state-of-the-art information in accessible format enabling improved management of cats under our care. This book is equally relevant to veterinary practitioners, students, nurses and technicians, and with its emphasis on the management of both acute and chronic pain it will serve as an invaluable resource in any clinic.
The concise and clear layout of this book makes accessing information particularly easy for the busy practitioner. The text is concise, practical, relevant, and addresses exactly the sorts of questions and issues that occur in day-to-day veterinary practice. Chapters are well illustrated and authored by an outstanding collection of international experts in feline anesthesia and analgesia.
It is perhaps unusual to look at a book's table of contents and to look forward to reading every single chapter in the publication. I can honestly say that is the case with this book though. Much thought has gone into its structure, the subjects covered, and the way they are addressed. I hope and believe that this book will be very widely read and used. For anyone purchasing the book, it is destined to be something that is used on a daily basis in the clinic, and will not be a book that simply collects dust on the shelf!
On a personal note, I am passionate about feline welfare – I have also known Paulo, Sheilah, and Polly for a number of years and I know how passionate they are too about improving cat welfare through better clinical application of analgesia. With this book, any veterinarian or nurse/technician will find a wealth of practical information that will directly impact their everyday clinical work, and will improve the lives of the cats that are under their care. I can offer no higher recommendation – this book will improve your ability to care for your feline patients and improve their welfare, and as such it deserves to have a place in every small animal clinic.
Dr. Andy Sparkes BVetMed PhD DipECVIM MANZCVS MRCVSVeterinary Director, International Cat Care and International Society of Feline Medicinewww.icatcare.org
Contributors
Graeme Doodnaught
Resident in Veterinary Anesthesia and Analgesia
Department of Clinical Sciences Faculty of Veterinary Medicine Université de Montréal
3200 Rue Sicotte
Saint-Hyacinthe, QC J2S2M2
Canada
Craig B. Johnson
Professor of Veterinary Neurophysiology Institute of Veterinary, Animal and Biomedical Sciences
College of Sciences
Massey University Private Bag 11 222
Palmerston North
New Zealand
Duncan Lascelles
Professor of Small Animal Surgery and Pain Management Comparative Pain Research Laboratory
College of Veterinary Medicine
North Carolina State University
1060 William Moore Drive
Raleigh, NC 27607
United States
Beatriz Monteiro
PhD Candidate in Veterinary Pharmacology
Vanier Scholar
Department of Biomedical Sciences Faculty of Veterinary Medicine Université de Montréal
3200 Rue Sicotte
Saint-Hyacinthe, QC J2S2M2
Canada
Daniel Pang
Associate Professor of Veterinary Anesthesiology
Department of Clinical Sciences Faculty of Veterinary Medicine Université de Montréal
3200 Rue Sicotte
Saint-Hyacinthe, QC J2S2M2
Canada
Peter Pascoe
Professor of Anesthesia and Critical Patient Care
Department of Surgical and Radiological Sciences
School of Veterinary Medicine
1 Shields Ave
University of California
Davis, CA 95616
United States
Bruno Pypendop
Professor of Veterinary Anesthesiology
Department of Surgical and Radiological Sciences
School of Veterinary Medicine
University of California
One Shields Avenue
Davis, CA 95616
United States
Sheilah Robertson
Senior Medical Director
Lap of Love Veterinary Hospice
17804 US-41, Lutz, FL 33549
United States
Bradley Simon
Assistant Professor of Veterinary Anesthesiology
Department of Small Animal Clinical Sciences
College of Veterinary Medicine and Biomedical Sciences, Texas A&M University
402 Raymond Stotzer Pkwy
College Station, TX 77843-4474
United States
Francesco Staffieri
Associate Professor of Veterinary Anesthesiology
Department of Emergency and Organ Transplantation, Section of Veterinary Clinics and Animal Production University of Bari
SP per Casamassima km 3, 70010 Valenzano
Bari
Italy
Paulo Steagall
Associate Professor of Veterinary Anesthesiology
Department of Clinical Sciences Faculty of Veterinary Medicine
Université de Montréal
3200 Rue Sicotte
Saint-Hyacinthe, QC J2S2M2
Canada
Polly Taylor
Independent Consultant in Veterinary Anaesthesia Taylor Monroe
Little Downham
Nr. Ely
Cambs CB6 2TY
United Kingdom
Eric Troncy
Professor of Veterinary Pharmacology
Department of Biomedical Sciences Faculty of Veterinary Medicine
Université de Montréal
3200 Rue Sicotte
Saint-Hyacinthe, QC J2S2M2
Canada
1Handling, Restraint, and Preanesthetic Assessment
Graeme Doodnaught and Paulo Steagall
Université de Montréal, Saint-Hyacinthe, Canada
Key Points
Behavioral considerations
Handling methods and physical restraint
Routes of drug administration
Airway management
Preanesthetic evaluation
Mortality and morbidity in feline anesthesia
Introduction
The pet cat population has grown over the last few decades, as has our understanding of disease prevention and treatment in this species. Despite population growth, fewer cats visit a veterinary clinic on a regular basis when compared with dogs. Cat owners often avoid veterinary visits as transportation of the cat to the clinic may be stressful. Handling, appropriate physical examination, knowledge of behavior, and preanesthetic assessment are essential components of feline anesthesia and analgesia.
Box 1.1: Cat-friendly Techniques in Clinical Practice
Safe handling and cat-friendly practices minimize stress, fear, anxiety, and potential personnel injuries related to aggression. They are key components of veterinary care for the anesthetist and staff members.
A cat-friendly practice will provide an environment that reduces the stress of veterinary consultation and hospitalization. More information can be found at http://icatcare.org (June 24, 2017). These practices involve:
A calm, safe, and quiet clinic with cat-designated areas or cat-only appointment times
Gentle and efficient physical examination and treatment
Client education on transporting the cat to and from the clinic
Client communication about feline anesthesia and analgesia
Handling and Restraint
Each cat is unique and can exhibit a wide range of behaviors. Experienced handlers will often adapt their approach and handling technique to suit each patient. While there is no substitute for “experience”, some principles exist to aid in the restraint of most cats. The mantras “go slow to go fast” and “less is more” are commonplace. Good feline handling revolves around the premise of de-escalation, where the handler avoids potential actions that may elevate a patient's stress. De-escalation minimizes noxious visual, auditory, and olfactory stimuli that could lead to avoidance or aggressive behavior. It should be noted that the major cause of defensive or aggressive behavior is fear. Cats have limited appeasement behaviors, making it difficult to calm them once they are distressed. Thus, avoiding these behavioral triggers is critical to success.
To facilitate handling throughout life, kittens should be encouraged to interact with people, animals, and new environments between 2 and 7 weeks of age. With all ages of cats, positive reinforcement techniques (e.g. rewarding with food, play, brushing) along with behavioral therapy in difficult individuals, help to reduce the stress and anxiety associated with veterinary visits.
Most cats in a calm environment will readily explore their surroundings. Anxious or fearful individuals will tend to remain within their carriers. The cat should be handled with patience and a positive attitude throughout the physical examination. Minimal restraint is required to perform a full physical examination in most cats. Gentle touch and petting around the head and neck are generally well tolerated, and allow for minor manipulations without the need for physical restraint (Figure 1.1a, b, c). Timid or fearful individuals who choose to remain in the carrier should be allowed to do so. The top of a carrier may be removed and an examination can be performed with the cat still inside (Box 1.2).
Box 1.2: Safe Handling in Feline Practice
Consider using top-opening carriers and baskets for transporting cats into the clinic. This allows for easy handling and provides a safe and secure environment.
Figure 1.1 A cat-friendly approach in a hospital setting. (a) This cat explores the examination room and its surroundings. (b) The handler gently pets the cat to control its movement without using forcible restraint. (c) Placing the hands under the chin allows for better control of the head and neck.
It is understandable that most medical procedures in cats require some level of restraint. This makes treatments and procedures safer for both cat and handler. While immobilization is often required, the approach should still be gentle. Figure 1.2 shows common methods of control.
Figure 1.2 Restraint for common procedures in cats. (a) Most cats will tolerate gentle extension of the neck to expose the jugular veins for blood sampling. In this image the jugular vein is occluded with the cat in lateral recumbency. (b) Restraint of the forelimb for cephalic blood sampling or IV catheterization. The handler is preventing the cat from backward movement by applying gentle pressure over the cat's hind limbs. Using the same arm, the handler is extending the right limb forward with three fingers behind the elbow to prevent retraction of the limb, and rotating and raising the cephalic vein with their first and second digits. (c) Restraint of the hind limb for medial saphenous blood sampling or IV catheterization. The cat is restrained in lateral recumbency with the dependent limb intended for venous sampling. The handler uses one hand to restrain the contralateral (upper) hind limb and apply medio-lateral pressure over the vein proximal to the sampling site. Once the vessel is visualized, the clinician directs the needle in a distal to proximal direction while maintaining control of the lower limb with the opposite hand. (d) This cat is allowed to stand freely on the treatment table and is only restrained by gentle control of the head and neck. This allows free access to the epaxial muscles for intramuscular injection.
Scruffing
Scruffing is a controversial method of restraint. Many clinics have a “no-scruffing” policy. Scruffing should be regarded as a last resort for physical restraint to avoid injuries and accidents. For these exceptional cases, the cat is gently grasped by the skin over the dorsum of the neck and scapulae, and minimal (firm) pressure is maintained. The method should certainly not be used if there is already pain or discomfort present. It is important to highlight that scruffing may lead to fear-based aggression and further escalation of stress. The American Association of Feline Practitioners (AAFP) and the International Society of Feline Medicine (ISFM) state that the technique should be used sparingly. A cat should never have its full weight suspended from the scruff.
The Fearful Cat
Fear is the most common cause of aggression in hospitalized cats. De-escalation techniques do not always work in fearful individuals. These cats exhibit strong avoidance or aggressive behavior making handling difficult. In this situation, chemical restraint should be considered before any manipulation (Chapter 3). To assist in the physical restraint of these patients, use of appropriate handling equipment is recommended (description of techniques to follow). In these cases, the equipment for IV catheter placement, and for anesthetic induction, maintenance, and monitoring should be ready.
Box 1.3: The Handling Equipment
Handling equipment should be:
Safe for the cat and handler
In good working order with frequent “check ups”
Easy to use and to clean
Suitable for the intended task
Some techniques used for appropriate restraint of the fearful and/or aggressive cat are listed below:
Towels or blankets
are commonly used for restraining fearful cats. They are often successful in protecting the handler from injury. By covering the patient, they give the cat a place to hide, minimizing visual and auditory stimulation. The handler maintains good dexterity and can assist with the procedure
Synthetic feline facial pheromones
mimic natural pheromones that are secreted by cats via facial rubbing when they are comfortable and when they mark their territories. These products have been shown to decrease stress and facilitate handling of some cats
Masks
or
hoods
may assist with physical restraint of some cats by limiting visual stimulation. A well-fitted mask will also protect the handler from bites. They are variably tolerated and require judicious use
Bags
for restraint protect individuals from aggressive cats. Openings in these bags allow access to the limbs and head
Feral cats may require the use of
squeeze cages, humane traps
or
nets
for drug administration. Their application is limited to capture and restraint of cats for injection. Nets are used in exceptional conditions such as when a cat escapes or where there are extremely limited facilities. Such equipment can easily cause trauma if not used properly
Anesthetic induction chambers
may be used to anesthetize cats. This requires minimal restraint but placing the cat inside the chamber can be a challenge. While the absence of restraint is arguably better for the cat, there is potential for environmental contamination and exposure of personnel with volatile anesthetics. A fearful cat can be briefly restrained using a towel or cat bag for mask induction using volatile anesthetic agents. Techniques for induction of general anesthesia are discussed in
Chapters 4
and
6
Leather handling gauntlets
or
gloves
can protect the handler from an aggressive cat but they limit dexterity. They should be used only as a last resource for restraint. Leather is also difficult to clean and repeated disinfection is required
Blood Sampling
Restraint for blood sampling can be performed in many ways. The jugular vein is a common site as it is easily identified and allows rapid withdrawal of large volumes of blood compared with distal veins (Figure 1.2a). The handler extends the head and neck with the cat in a sternal or lateral position. The clinician approaches the vein with the needle directed either in a cranio-caudal (Figure 1.2a) or caudo-cranial direction. The use of a 23-G 1.6 cm (5/8th inch) needle and a small volume syringe (1–3 mL) is recommended.
Peripheral blood sampling, for example from the cephalic vein (Figure 1.2b), may be used for low-volume sample collection, or where jugular sampling is contraindicated (e.g. coagulopathies, increased intracranial or intraocular pressure). Another common site for sampling is the medial saphenous vein (Figure 1.2c). To limit repeated venipuncture, the blood that is collected in the hub of a catheter's stylet can be used for a basic blood panel during the preoperative period (Table 1.1).
Table 1.1 Values for basic blood panel in cats.
Hematocrit (packed cell volume)
30–50%
Total solids (total protein)
60–85 g/L
Blood urea nitrogen
170–320 g/L
Calcium
85–110 g/L
Potassium
3.7–5.4 mEq/L
Drug Administration
A number of routes of administration are available for drug delivery, and the choice will depend on both drug selection and intended purpose.
Intravenous (IV
) administration is the most efficacious and reliable method of drug delivery. It is commonly used for anesthetic induction, or for analgesic drugs when a catheter is in place
The intramuscular (IM) route is commonly used for premedication. Any skeletal muscle may be used but large-bellied and superficial muscles are preferred. The epaxial and muscles of the cranial and caudal thigh are often chosen (
Figure
1.2d
); if using the hind limb, the cranial thigh is more reliable. When using the caudal thigh, it is easy to miss muscle tissue and inject into fascial planes. The location of major blood vessels and nerves is important when selecting an injection site. For example, the sciatic nerve runs beneath the
biceps femoris
in the caudo-lateral thigh, and may be inadvertently injured. Aspiration should precede injection to avoid unintended intravascular injection
The
subcutaneous (SC)
route is used for perioperative administration of drugs such as nonsteroidal inflammatory drugs. This route can also accommodate large volumes of crystalloid fluids when intravenous fluid therapy is not possible. Most conscious cats will tolerate injection between the shoulder blades
Buccal or oral transmucosal
(OTM) administration is not commonly used in hospital settings, as other routes are usually an option. However, it can be used as a less invasive route of administration during long-term hospitalization or “home care.” It is accomplished by inserting the syringe tip into the cat's mouth and gently squeezing the syringe contents into the cheek pouch; swallowing must be avoided to allow transmucosal absorption and prevent first-pass hepatic metabolism
IV Catheterization
A wide array of IV catheter types exists in veterinary practice. These are commonly inserted into the cephalic or medial saphenous veins. Catheterization of these vessels is often performed following premedication (Chapter 3). Intravenous catheterization allows easy drug titration during anesthetic induction, administration of fluids, emergency intervention, and minimizes the need for multiple SC or IM injections in the perioperative period. Use of topical local anesthetic creams can facilitate placement of catheters (Box 1.4). The ideal catheter material is inert, long-lasting, and atraumatic. Catheters should be placed using a sterile technique.
Silicone catheters are good choices for long-term cannulation. In cats requiring extended hospitalization, central venous catheters (18- or 21-G) are placed using the modified Seldinger method, peel-away introducers, or cut-down techniques. Aseptic technique is mandatory for the placement of long term catheters.
Box 1.4: Intravenous Catheterization in Clinical Practice Using Local Anesthetic Creams
Smaller gauge (≤ 22-G) catheters are commonly used for the cephalic and medial saphenous veins in cats. Application of topical anesthetics (e.g. EMLA; eutectic mixture of local anesthetics, a combination of lidocaine 2.5% and prilocaine 2.5%) at least 30 minutes before catheterization desensitizes the skin, thereby reducing the stress of the whole procedure. This technique can also be used for jugular venipuncture enabling minimal restraint. The cream is applied and covered with an impermeable and nonabsorbent dressing. The use of gloves is recommended, as the cream will anesthetize human skin. IV catheters should be examined daily for signs of infection and skin irritation, and to confirm patency. Taping should not be overtight otherwise distal limb edema may occur.
Intubation and Airway Management
Induction of anesthesia is commonly followed by maintenance with a volatile anesthetic and oxygen. Endotracheal intubation protects the airway, minimizing the risk of aspiration if regurgitation occurs; it also enables delivery of oxygen and anesthetic, and facilitates ventilation. Figure 1.3 shows appropriate positioning for intubation in a cat.
Figure 1.3 Restraint for intubation: with the cat in sternal recumbency, the handler gently extends the neck and head. Either the handler or the individual performing the intubation opens the mouth by exteriorizing the tongue. In this position the larynx is easily visualized with a laryngoscope enabling application of local anesthetic followed by intubation. The laryngoscope (or other instrument) should be used to exteriorize the tongue as intraoral manipulation of cats in a light plane of anesthesia may lead to a reflex bite.
The challenges and complications (i.e. laryngospasm, laryngeal trauma, tracheal rupture or necrosis and airway obstruction) of intubation in cats (Box 1.5) are discussed in Chapters 2 and 10. Most adult cats can be intubated with a 3.5–5 mm internal diameter endotracheal tube (ETT). Cuff inflation should not require more than 1.5 mL of air using a small syringe. Small increments of air (0.5 mLs) should be injected at a time into the pilot balloon until a seal is achieved when the pressure in the breathing circuit is 16–18 cmH2O. Pressure within the high-volume low-pressure cuff can be monitored using a special device (Posey Cufflator Endotracheal Tube Inflator and Manometer®). This will avoid high cuff pressures and the risk of airway trauma. Overlong ETT may cause a range of problems (Chapter 10) and should be cut to an appropriate length before insertion (Box 1.5; Figure 1.4a, b, c).
Figure 1.4 (a) The tip of the endotracheal tube should not reach further than the thoracic inlet. (b) Endotracheal tubes should be measured before use; they should reach from the tip of the shoulder (thoracic inlet) to the incisor teeth. (c) Endotracheal tubes should be cut to the correct length prior to use. Excess length adds dead space.
It is strongly recommended that the cat is disconnected from the breathing system when turning is required during anesthesia. This will prevent extubation and inadvertent trauma. All endotracheal tubes can damage the mucociliary apparatus, which moves particles in an orad direction, and can cause direct damage to the tracheal endothelium. If an endotracheal tube is used, the tip should not extend beyond the thoracic inlet (point of the shoulder); if a tracheal tear does occur, the prognosis is worse for an intrathoracic tear and it is more difficult to repair than an extrathoracic injury (Chapter 10).
Box 1.5: Endotracheal Tubes
Cuffed Tubes
The inflatable cuff seals the airway but has the potential to cause damage
The cuff and its pilot tube occupy a substantial proportion of the tube diameter, potentially reducing airway size. Modern tube construction minimizes this effect (e.g. soft silicone)
Potential for damage caused by the cuff (
Chapter 10
)
An inflated cuff may cause local pressure ischemia to the tracheal lining (
Chapter 10
)
Lubricant gel on the cuff enhances the seal at a given pressure
Cuffed tubes are required for IPPV (or a supraglottic airway device see below) and reduce the risks of fluid aspiration
Noncuffed Tubes
Used to be considered best for cats
Avoid potential for cuff-induced tracheal damage but more difficult to seal the airway
Require pharyngeal packing to prevent fluid entering the airway
The Cole tube is cuffless; the seal is produced by advancing the shoulder until it impacts onto the larynx. These are difficult to place reliably without causing damage and are now rarely used
Supraglottic Airway Devices
This device does not enter the trachea and ends above the larynx
Distal elliptical component with an inflatable bladder on the dorsal aspect seals the airway
The v-gel
®
developed for cats is easy to place
Limited evidence so far suggests that the v-gel
®
is less likely to cause damage than standard ETT
Suitable for IPPV
Endotracheal Tube Length
Overlong tubes may cause excessive airway dead space, tracheal tears, and endobronchial intubation (
Chapter 10
)
The length of the endotracheal tube should be measured in each cat before placement (
Figure
1.4b
) and cut as needed (
Figure
1.4c
)
The endotracheal tube should reach from the incisor teeth to the point of the shoulder
The tip should reach the mid to lower third of the trachea and not enter the thorax
The connector end can be cut to shorten the tube
A stylet can be used cautiously to increase dexterity especially with silicone ETT. The tip of the stylet should never go through the distal part of the ETT.
Supraglottic airway devices (SGAD) (e.g. the v-gel®) are another option for airway management in cats. The device comprises a tube with a distal elliptical component that has an inflatable bladder on the dorsal aspect that is used when needed to create a better seal (Figure 1.5a). It is a practical alternative to endotracheal intubation in cats, leading to a lower incidence of upper airway discomfort after extubation when compared with an endotracheal tube. The v-gel® can be inserted at a more superficial depth of anesthesia than an endotracheal tube. It can be used for mechanical ventilation and a variety of procedures. Placement is relatively easy and can be performed by inexperienced individuals. However, v-gels are much more expensive than endotracheal tubes.
Figure 1.5 (a) A v-gel® has been selected, lubricated and is sitting in its cradle to avoid contamination; a side stream capnograph has been attached to confirm proper placement. (b) The v-gel® has been placed and secured in place.
Preanesthetic Assessment
The purpose of the preanesthetic examination is to assess the suitability of a patient for anesthesia, prevent complications, assess risks, and determine whether any special consideration, material, preparation or equipment is required. Planning is a key component to prevent anesthetic-induced complications such as hypothermia, hypoventilation, bradycardia, and hypotension.
A checklist for preanesthetic assessment is recommended. The Association of Veterinary Anaesthetists (AVA) have examples available for download at http://www.ava.eu.com/information/checklists/ (accessed June 24, 2017). The checklist should include:
Patient identification, history, and signalment
– A full history should be taken, with emphasis on previous anesthetic and surgical procedures, as well as current medication. Age is particularly important in identifying individuals at risk (pediatrics or geriatrics)
Concomitant diseases/conditions
– These have a potential impact on anesthesia and pain management. Particular considerations apply for managing anesthesia of neonatal, pediatric, and pregnant cats as well as for those with, for instance, diabetes, cardiomyopathy, and urinary tract obstruction (
Chapter 9
). Some cats may require stabilization before anesthesia
Physical examination
– Emphasis should be given to the cardiovascular, respiratory, hepatic, and renal systems as their roles in perfusion, oxygenation, and drug metabolism affect many aspects of anesthesia. Unfortunately, the hospital visit itself is stressful, generally elevating heart and respiratory rate, blood pressure, and body temperature (
Box
1.6). Therefore, recognition of stress and anxiety is important in clinical assessment of these values. Body condition scoring allows objective recognition of extremes in body weight, which may increase the patient's risk. An accurate weight should be obtained
Risks associated with the surgical procedure
– This includes planning for the potential of bleeding and perioperative pain, the effects of positioning, technique (e.g. laparoscopic procedures) and duration. Crossmatching and blood typing may be required for some cases and is discussed in
Chapter 8
. Certain surgical procedures require special equipment, materials or changes in the layout of the operating room. Team meetings prior to a nonroutine procedure prevent mistakes and misunderstandings, and save valuable time
Fasting
– Fasting has been recommended to allow time for gastric emptying, which should decrease the risk of vomiting, regurgitation, and aspiration. Withholding food for periods from 2 to 10 hours have been suggested; short fasting times are appropriate in some instances, for example pediatric patients and cats with diabetes mellitus. The anesthetist should never assume that fasting will result in an empty stomach and must be prepared to act if vomiting occurs in the perioperative period (
Chapter 10
)
Risk assessment (ASA status)
– Full discussion of all possible presenting conditions is beyond the scope of this chapter, but interpretation of clinical data should allow the patient's health status to be classified according to the American Society of Anesthesiologists (ASA). The five-point scale used in people is adapted in
Table
1.2
for use in veterinary medicine. ASA status is correlated with risk of anesthetic death
Set up
– All materials and equipment should be tested and ready before general anesthesia is induced. Supplies include tape, catheters, eye lubricant, flush solution, airway devices, laryngoscope, stylet, anesthetic record, surgical preparation solutions, gauze and fluid bags. Monitors should be calibrated beforehand. Anesthetic machines and breathing systems must be in good working condition
Box 1.6: Normal Physiological Values in Cats
Resting heart rate:
120–200 beats per minute
Resting respiration rate:
20–30 breaths per minute
Rectal Temperature:
37.5–38.9 °C
Table 1.2 ASA physical status classification system.
Source: ASA House of Delegates. (2014) ASA Physical Status Classification System, American Society of Anesthesiologists, www.asahq.org/resources/clinical-information/asa-physical-status-classification-system (accessed June 24, 2017).
ASA classification
a
)
Definition
ASA I
A normal healthy patient
ASA II
A patient with mild systemic disease
ASA III
A patient with severe systemic disease
ASA IV
A patient with severe systemic disease that is a constant threat to life
ASA V
A moribund patient who is not expected to survive without the operation
Note:
a
) Each classification is further subdivided with the inclusion of an “E” to represent an emergency surgery, where delay may affect outcome.
Ancillary tests are recommended when abnormalities are identified from the history and physical examination. This may include a basic blood panel (Table 1.1). Low hematocrit may indicate anemia, limiting the patient's ability to carry oxygen. Decreases in total protein may increase the effect of highly protein bound drugs and may also require adjustment of the anesthetic dose and fluid therapy. Many clinicians extend their screening to include a complete blood count, biochemical panel, total thyroxin (T4), and a urinalysis in geriatric patients. The rationale behind geriatric screening is the detection of subclinical disease despite normal clinical findings. However, it is important to highlight that blood collection may cause stress and results will not change the anesthetic plan in the majority of cases.
Hypertrophic cardiomyopathy is often asymptomatic in cats and can be only diagnosed using echocardiography. A workup is recommended when murmurs are auscultated and if cardiovascular disease is suspected as this could change the anesthetic protocol (Chapters 9 and 10).
Risk Factors, Morbidity, and Mortality
The risk of anesthetic-related death in cats varies between 0.1% and 0.3%. A study in the United Kingdom reported an overall mortality rate of 0.24% in cats, which was higher than the 0.17% reported in dogs. Healthy cats (ASA I to II) are >12 times more likely to survive anesthesia than those that are sick (ASA III to V). This demonstrates the importance of preanesthetic assessment and health-status classification. An ASA classification of ≥ 3 should not discourage clinicians from important procedural interventions, but the increased risk should be taken into account when the anesthetic protocol and monitoring are planned and should be discussed with the owner. Since disease increases the risk of anesthetic-related mortality, elective procedures should be delayed until the patient is stabilized and/or treated. Perioperative monitoring is crucial because it is associated with reduced anesthetic risk. Almost two-thirds of all anesthetic-related deaths in cats occurred in the postoperative period, in particular during the first three hours after extubation (Table 1.3) (Chapter 10).
Table 1.3 Timing, number, and percentage of anesthetic- and sedation-related deaths in dogs, cats, and rabbits.
Source: Brodbelt 2008. Reproduced with permission of John Wiley & Sons.
Timing of death
Dogs (%)
Cats (%)
Rabbits (%)
After premedication
1 (1)
2 (1)
0
Induction of anesthesia
9 (6)
14 (8)
6 (6)
Maintenance of anesthesia
68 (46)
53 (30)
29 (30)
Postoperative death
a
)
70 (47)
106 (61)
62 (64)
0–3 hours post-op
31
66
26
3–6 hours post-op
11
9
7
6–12 hours post-op
12
7
13
12–24 hours post-op
13
12
9
24–48 hours post-op
3
10
3
Unknown time
0
2
4
Total
148 (100)
175 (100)
97 (100)
Note:
a
) Postoperative deaths were additionally categorized by time after anesthesia. The percentage values are given in parentheses.
Other risk factors associated with perioperative mortality in cats include:
Extremes of age
Neonatal and geriatric cats are at higher risk of anesthetic-induced fatality (
Chapter 9
). However, healthy kittens over 1 kg tolerate general anesthesia remarkably well
Extremes of body weight
Weight loss in cats may indicate underlying disease (e.g. hyperthyroidism, renal disease, lymphoma), which may affect drug metabolism, protein binding, and cardiovascular reserve. Small cats may be at a greater risk for becoming hypothermic. On the other hand, obesity may be associated with disease (e.g. cardiovascular disease, diabetes, lower urinary-tract disease). Obese cats (
Figure
1.6
) have increased intra-abdominal and thoracic fat, potentially limiting respiratory function when in dorsal recumbency and potentially putting them at higher risk of airway obstruction (
Chapter 10
). Obesity increases the volume of distribution for lipophilic drugs into tissues that do not actively participate in drug metabolism
Endotracheal intubation
Endotracheal intubation protects the airway while providing means of oxygenation, ventilation, and administration of anesthetic gas mixtures. A study reported that 63% of cats that died after surgery were intubated compared to 48% of nonintubated cats. One of the most common causes of perioperative death in cats is airway obstruction, which may be a result of laryngeal trauma during intubation (
Chapter 10
)
Absence of, or excessive, fluid therapy
The benefits and risks of fluid administration during anesthesia are discussed in
Chapter 8
. Cats are at higher risk of fluid overload when compared with dogs. Administration of fluids has been associated with increased anesthetic-induced fatality (
Chapter 10
)
Spay-neuter clinics
A retrospective study from a large volume spay-neuter clinic reported the risk of mortality in cats as 0.05%, 5 times that of dogs in the same setting. The risk of mortality in females was twice that of males and most deaths occurred post-operatively. The lower mortality risk in these cats compared to the Confidential Enquiry into Perioperative Small Animal Fatality (CEPSAF) study is probably due to the young, healthy population and the skills of experienced veterinarians.
Figure 1.6 An obese cat (9.5 kg) immediately after the end of abdominal laparotomy for foreign body removal. Extremes of body weight are associated with increased risk of perioperative mortality in cats.
Further Reading
American Society of Anesthesiologists (2014)
ASA Physical Status Classification System,
www.asahq.org/resources/clinical-information/asa-physical-status-classification-system
(accessed June 24, 2017).
Barletta, M., Kleine, S. A., and Quandt, J. E. (2015) Assessment of v-gel supraglottic airway device placement in cats performed by inexperienced veterinary students.
Veterinary Record
177
, 523.
Brodbelt, D. C., Blissitt, K. J., Hammond, R. A.,
et al.
(2008) The risk of death: The Confidential Enquiry into Perioperative Small Animal Fatalities.
Veterinary Anaesthesia and Analgesia
35
, 365–373.
Brodbelt, D. C., Pfeiffer, D. U., Young, L. E.,
et al
. (2007) Risk factors for anaesthetic-related death in cats: Results from the Confidential Enquiry into Perioperative Small Animal Fatalities (CEPSAF).
British Journal of Anaesthesia
99
, 617–623.
Carney, H. C., Little, S., Brownlee-Tomasso, D.,
et al
. (2012) AAFP and ISFM feline-friendly nursing care guidelines.
Journal of Feline Medicine and Surgery
14
, 337–349.
Kronen, P. W., Ludders, J. W., Erb, H. N.,
et al
. (2006) A synthetic fraction of feline facial pheromones calms but does not reduce struggling in cats before venous catheterization.
Veterinary Anaesthesia and Analgesia
33
, 258–265.
Levy, J. K., Bard, K. M., Tucker, S. J.,
et al.
(2017) Perioperative mortality in cats and dogs undergoing spay or castration at a high-volume clinic.
Veterinary Journal
224
, 11–15.
Prasse, S. A., Schrack, J., Wenger, S.,
et al
. Clinical evaluation of the v-gel supraglottic airway device in comparison with a classical laryngeal mask and endotracheal intubation in cats during spontaneous and controlled mechanical ventilation.
Veterinary Anaesthesia and Analgesia
43
, 55–62.
Porters, N., de Rooster, H., Moons, C. P.,
et al
. (2015) Prepubertal gonadectomy in cats: Different injectable anaesthetic combinations and comparison with gonadectomy at traditional age.
Journal of Feline Medicine and Surgery
17
, 458–467.
Quimby, J. M., Smith, M. L., and Lunn, K. F. (2011) Evaluation of the effects of hospital visit stress on physiologic parameters in the cat.
Journal of Feline Medicine and Surgery
13
, 733–737.
Rodan, I. (2010) Understanding feline behaviour and application for appropriate handling and management.
Topics in Companion Animal Medicine
25
, 178–188.
Rodan, I., Sundahl, E., Carney, H.,
et al
. (2011) AAFP and ISFM Feline-friendly handling guidelines.
Journal of Feline Medicine and Surgery
13
, 364–375.
Thrall, M. A., Weiser, G., Allison, R. W., and Campbell, T. W. (2012)
Veterinary Hematology and Clinical Chemistry
, 2nd edn. Wiley-Blackwell, Ames, IA.
Turner, D. C., and Bateson, P. (2014)
The Domestic Cat: The Biology of its Behaviour
, 3rd edn. Cambridge University Press, New York, NY.
van Oostrom, H., Krauss, M. W., and Sap, R. (2013) A comparison between the v-gel supraglottic airway device and the cuffed endotracheal tube for airway management in spontaneously breathing cats during isoflurane anaesthesia.
Veterinary Anaesthesia and Analgesia
40
, 265–271.
Wagner, K. A., Gibbon, K. J., Strom, T. L.,
et al
. (2006) Adverse effects of EMLA (lidocaine/prilocaine) cream and efficacy for the placement of jugular catheters in hospitalized cats.
Journal of Feline Medicine and Surgery
6
, 141–144.
Wallinder, E., Hibbert, A., Rudd, S.,
et al
. (2012) Are hospitalised cats stressed by observing another cat undergoing routine clinical examination?
Journal of Feline Medicine and Surgery
14
, 655.
2Anatomy, Physiology, and Pharmacology
Bradley Simon1 and Paulo Steagall2
1Texas A&M University, College Station, TX, United States
2Université de Montréal, Saint-Hyacinthe, Canada
Key Points
Unique anatomical and physiological features of each organ system in the cat
Overview of pharmacological effects of sedatives, analgesics, and anesthetics on each system
Peculiarities of feline drug metabolism
Introduction
Assessment of physiological function can be difficult in cats due to their natural behavior, high sympathetic tone, disease, the effects of drugs, and lack of patient compliance in a hospital setting. This chapter describes specific features of normal feline physiology and anatomy, and includes a discussion of the effects of anesthetic and analgesic agents on body systems. Based on this information, the anesthetist may tailor an anesthetic protocol for the individual cat and prevent potential complications during anesthesia.
Cardiovascular System
Anatomy
The heart contains four chambers (right and left atria, right and left ventricle), and separates the arterial and venous systems. It is perfused by the right and left coronary arteries. The right ventricle pumps blood through the pulmonary valve into the pulmonary trunk and then into the pulmonary circulation where gas exchange takes place. The left ventricle pumps blood through the aortic valve into the aorta and out into the systemic circulation. Aortic blood enters arteries and then arterioles, which are heavily innervated and surrounded with smooth muscle to regulate tissue blood flow.
The dorsal pedal artery is palpated on the dorsomedial aspect of the pelvic limb, distal to the tarsus, and the coccygeal artery on the ventral aspect of the tail. These arteries can be used for invasive blood pressure monitoring during anesthesia (Chapter 7). The radial artery is palpated on the palmar aspect of the forelimb, just distal to the carpal joint, and is often used for pulse detection and blood-pressure monitoring using Doppler ultrasound. Blood enters the capillaries where nutrient, waste, and fluid exchange occur. Arteriovenous (AV) anastomoses connect arterioles to venules and respond to α1 and α2 adrenergic stimulation. These AV anastomoses also play an intrinsic role in thermoregulation and are found in distal extremities and skin. Venules and veins transport blood from capillaries back to the heart and are a reservoir for 60–70% of the total blood volume during rest. They also possess α1 and α2 adrenergic receptors that alter vascular tone. The cephalic vein, medial saphenous, and the external jugular vein are used for venipuncture or intravenous catheter placement.
The chemoreceptors (pH, PCO2, PO2), baroreceptors (vascular and cardiac stretch receptors), local control mechanisms (PO2, PCO2, lactate, H+), and the parasympathetic and sympathetic nervous systems play a fundamental role in acute blood pressure and heart-rate regulation.
Feline blood is unique when compared with other species, and this is further discussed in Chapter 8.
In cats, the heart sits in a more horizontal plane than in the dog, with greater sternal contact. Feline auscultation is best performed over the left and right parasternum, enabling the clinician to auscultate the following sounds (S):
S1: “lub” is associated with closure of the tricuspid and mitral valves, and is best auscultated at the costochondral junction over the right apex of the heart at the fourth and fifth intercostal spaces (tricuspid) and over the left apex at the left fifth intercostal space (mitral)
S2: “dub” is associated with closure of the pulmonary and aortic valves, and is loudest at the heart base, located medial to the triceps muscle on the left side at the third and fourth intercostal spaces
S3 and S4 are considered abnormal in cats and constitute a “gallop rhythm”. S3 may be associated with ventricular dilation or rapid ventricular filling during states of anemia, volume overload, dilated cardiomyopathy, and hypertrophic cardiomyopathy. S4 may be heard in patients with hypertrophic cardiomyopathy
The feline brain and retina receive the majority of their blood supply from the maxillary artery, which forms an arteriolar network known as the rete mirabile arteria maxillaris (Figure 2.1). The prolonged use of a mouth gag or wide opening of the jaw may compress the maxillary artery via the angular process of the mandible, leading to blindness and neurological dysfunction (Chapter 10). Opening the mouth narrows the distance between the medial aspect of the angular process of the mandible and the rostrolateral border of the tympanic bulla; the maxillary artery runs between these two osseous structures. In particular, spring-loaded mouth gags may reduce maxillary artery blood flow and compromise perfusion of the brain and retina. Mouth gags are no longer recommended in cats for dental procedures or endoscopy (Figure 2.2) (Chapter 10).
Figure 2.1 Magnetic resonance angiography of the head and neck of a cat. (1) maxillary artery; (2) external carotid artery. (a) normal blood flow with closed cat mouth; (b) severely decreased blood flow with open cat mouth. Source: Barton-Lamb 2013. Reproduced with permission of Elsevier.
Figure 2.2 The effects of the angular process on maxillary arterial blood flow in cats with mouth closed (A) and mouth open (B). Source: Barton-Lamb 2013. Reproduced with permission of Elsevier.
Cardiac Electrical Conductivity
The sinoatrial (SA) node contains specialized cardiac cells that allow spontaneous depolarization (automaticity) and is termed the “pacemaker”. Automaticity depends on the slow influx of calcium and sodium into the cardiac myocyte, and is affected by temperature, pH, oxygen, carbon dioxide (CO2), electrolytes, and hormones. Summation of the action potentials produced by all cardiac myocytes following SA node depolarization generates the electrocardiogram (ECG) (Figure 2.3a). The feline ECG (Figure 2.3b) can be difficult to interpret due to artifacts, rapid heart rate, and small electrical deflections. Electrolyte changes alter the ECG (for example in cats with hyperkalemia due to urinary tract obstruction) (Chapter 9).
Figure 2.3 (a) Feline electrocardiogram. (b) The feline electrocardiogram can be difficult to interpret due to artifacts and electrical deflections.
Physiology
The volume of blood ejected from the left ventricle per contraction is termed the stroke volume (SV) and is affected by preload, afterload, and contractility. Stroke volume multiplied by the heart rate (HR) determines cardiac output (CO). This equation (CO = SV × HR) is of paramount importance in understanding and treating hypotension and hypertension in the clinical setting.
The preload is the pressure of the blood creating stretch on the myocardium just before contraction. It is determined by the volume of blood returning from the systemic circulation (venous return)
The afterload is the pressure in the wall of the left ventricle during ejection. It is directly related to the systemic vascular resistance (SVR). Increased systemic vascular resistance (i.e. after administration of agonists of α
2
-adrenoreceptors) may decrease stroke volume
Cardiac contractility depends on the availability of intracellular calcium. Sympathetic activation, afterload, circulating catecholamines, and heart rate affect ventricular contractility
