Questions and Answers in Small Animal Anesthesia E-Book
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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Questions and Answers in Small Animal Anesthesia provides practical and logical guidance for a wide range of anesthesia questions commonly faced in veterinary medicine. * Gives concrete answers to questions about anesthesia likely to be faced in small animal practice * Explains why experienced anesthesiologists make the choices they do * Provides concise yet comprehensive coverage of anesthetic management using an engaging question-and-answer format * Covers dogs, cats, small mammals, and birds * Focuses on practical, clinically relevant information
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Veröffentlichungsjahr: 2015
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Table of Contents
Cover
Title Page
Copyright
Dedication
List of Contributors
Preface
Chapter 1: Patient Evaluation
References
Chapter 2: Owner Concerns
References
Chapter 3: Patient Preparation
References
Chapter 4: Anesthetic Machine and Equipment Check
References
Chapter 5: Pre-Anesthetic Sedative Drugs
References
Chapter 6: Opioids and Nonsteroidal Anti-Inflammatory Drugs
Opioids
Nonsteroidal anti-inflammatory drugs (NSAIDs)
References
Chapter 7: Anticholinergic Drugs
Reference
Chapter 8: Time to Premedicate
References
Chapter 9: Intravenous Access and Fluid Administration
References
Chapter 10: Intravenous Anesthetic Induction Drugs
References
Chapter 11: Inhalant Inductions
Reference
Chapter 12: Induction Techniques for the Really Sick Patient
References
Chapter 13: Inhalant Anesthetics
References
Chapter 14: Total Intravenous Anesthesia (TIVA)
References
Chapter 15: Anesthetic Monitoring Basics
References
Chapter 16: Normal Values for Anesthetized Patients
References
Chapter 17: Troubleshooting Hypotension
References
Chapter 18: Troubleshooting Hypoxemia
References
Chapter 19: Troubleshooting Hypercapnia and Hypocapnia
References
Chapter 20: Troubleshooting Hypothermia and Hyperthermia
References
Chapter 21: Common Arrhythmias in Anesthetized Patients
Chapter 22: Constant Rate Infusions
References
Chapter 23: Loco-Regional Anesthesia
References
Chapter 24: Troubleshooting Anesthetic Recovery
References
Chapter 25: Recognition and Assessment of Pain in Dogs
References
Chapter 26: Recognition and Assessment of Pain in Cats
Acute Pain
Chronic Pain
References
Chapter 27: Post-Operative Analgesia – Approaches and Options
References
Chapter 28: Anesthetic Considerations for Dental Prophylaxis and Oral Surgery
References
Chapter 29: Anesthetic Considerations for Neurologic Disease
References
Chapter 30: Anesthetic Considerations for Ocular Disease
References
Chapter 31: Anesthetic Considerations for Upper and Lower Respiratory Disease
References
Chapter 32: Anesthetic Considerations for Cardiovascular Disease
Patent Ductus Arteriosus (PDA)
Mitral Regurgitation (MR)
MR with Congestive Heart Failure (CHF)
Hypertrophic Cardiomyopathy (HCM)
References
Chapter 33: Anesthetic Considerations for Gastrointestinal Disease
References
Chapter 34: Anesthetic Considerations for Hepatic Disease
References
Chapter 35: Anesthetic Considerations for Renal Disease
References
Chapter 36: Anesthetic Considerations for Post-Renal Urinary Tract Disease
References
Chapter 37: Anesthetic Considerations for Endocrine Disease
Diseases of the Thyroid Gland
Diseases of the Adrenal Glands
Diabetes Mellitus
Pheochromocytoma
References
Chapter 38: Anesthetic Considerations for Orthopedic Surgery
References
Chapter 39: Anesthetic Management of Common Emergencies in Small Animals
Gastric Dilation-Volvulus
Gastric or Intestinal Foreign Bodies
Intervertebral Disk Disease
Hemoabdomen
References
Chapter 40: Anesthetic Management of Brachycephalic Breeds
References
Chapter 41: Anesthetic Considerations for Other Canine Breeds
References
Chapter 42: Anesthetic Considerations for Cats
References
Chapter 43: Anesthetic Management of Rabbits and Ferrets
References
Chapter 44: Anesthetic Management of Birds
References
Index
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Chapter 4: Anesthetic Machine and Equipment Check
Figure 4.1 Anesthesia machine components: oxygen is delivered to the machine from the hospital bulk supply (pipeline inlet) or the transport cylinders attached to the machine. An anesthetic breathing system connects to the common gas outlet.
Figure 4.2 Typical components of a non-rebreathing system.
Figure 4.3 Typical components of a circle rebreathing system.
Figure 4.4 Negative pressure leak check: the fresh gas outlet tubing has been disconnected from its attachment to the circle system. A surgical suction bulb is compressed, inserted into the tube, and released. The bulb should remain depressed for at least 10 s indicating a negligible leak (see text for further explanation).
Figure 4.5 Pressure check of a circle rebreathing system. The pop-off valve is closed, the Y-piece occluded, and the O
2
flush valve is activated to distend the bag and develop a pressure equal to 30 cm H
2
O.
Chapter 10: Intravenous Anesthetic Induction Drugs
Figure 10.1 Distribution to various tissues of an injectable anesthetic after a single intravenous dose. The dotted line (.......) indicates the drug concentration in the vessel rich groups which receive 75% of cardiac output (CO) and includes the brain, thus producing the anesthetic effect. Recovery from anesthesia occurs as the drug concentration is reduced in the brain, as drug re-enters the circulation to distribute to other tissues with lower CO. The skeletal muscle group drug concentration will rise less rapidly than the vessel rich group (dashed line ..__..__..__), and the drug concentration in fat (as well as connective tissue and bone) will rise even more slowly (solid line __________) due to its low percentage of cardiac output. Release of drug into the circulation from these last 2 groups of tissues can contribute to residual sedation following recovery from anesthesia.
Chapter 15: Anesthetic Monitoring Basics
Figure 15.1 Oxygen–hemoglobin dissociation curve. HB: hemoglobin, PO
2
: partial pressure of oxygen in the blood. Note that hemoglobin saturation does not significantly change when PO
2
> 100 mmHg due to the curve being flat, but hemoglobin saturation drops quickly when PO
2
< 60 mmHg.
Figure 15.2 Normal capnograph. The various phases are labeled I–IV. See text for details.
Chapter 17: Troubleshooting Hypotension
Figure 17.1 Factors that influence Mean Arterial Pressure (MAP)
Figure 17.2 Flow Chart for treatment of Hypotension
Chapter 19: Troubleshooting Hypercapnia and Hypocapnia
Figure 19.1 Relationship between arterial CO
2
and ventilation in the awake state and after opioid sedation in mammals.
Figure 19.2 (a) (top graph). Capnograph waveform appearance during hypercapnia. Note that Phase 3 is elevated above the normal value of 40 mmHg. (b) (bottom graph). Capnograph waveform when hypercapnia is secondary to inspired CO
2
, as, for example, with exhausted CO
2
absorbent or malfunctioning one-way valves.
Chapter 21: Common Arrhythmias in Anesthetized Patients
Figure 21.1 Sinus Rhythms.
A
. Normal Sinus Rhythm.
B
. 1
st
degree AV Block. Note the prolonged interval between the P and QRS complex, but every P wave is followed by a QRS.
C
. 2
nd
degree AV Block. Note that some P waves are not followed by a QRS and the overall rate is slow
D
. 3
rd
degree AV block. Note that the P waves occur independently and the QRS complexes have a wide and bizarre appearance with a slow rate
E
. Atrial Fibrillation. Note the undulating baseline, absence of discernable P waves, and the irregularly irregular pattern to the rhythm.
F.
ST segment depression. Note the abnormal “slurred” appearance of the ST interval.
Figure 21.2 Ventricular Abnormalities or Arrhythmias.
A
. Bundle Branch Block. Note the widened base of the QRS complex, sometimes with a step-like appearance at the upstroke of the Q or downstroke of the S components.
B.
Ventricular Tachycardia. Note the fast rate, absence of P waves, and rapid bizarre looking QRS complexes.
C.
Multi-form Ventricular Premature Complexes (VPC). Note that the wide and bizarre appearance of the VPCs changes along the sample strip.
D.
R-on-T phenomenon. Note that the T wave occurs very early and during completion of the QRS complex, rather than after it.
E.
Accelerated idioventricular rhythm. Note the presence of some P waves, and the relatively normal rate of the VPCs (i.e. > 45 beats/min and < 160 beats/min).
F.
Ventricular Bigeminy classic for thiobarbiturate drugs. Note that a normal beat (P-QRS-T) alternates with a VPC. This rhythm is usually transient and resolves a few minutes after thiobarbiturate administration.
Chapter 23: Loco-Regional Anesthesia
Figure 23.1 Anatomy of the epidural space in the dog. (a) Aseptic needle placement, using sterile surgical gloves, into the lumbosacral epidural space of a dog (
A
) and catheter placement for continuous epidural anesthesia using a local anesthetic and/or analgesia using an opioid (
B
). (b) Dorsal view. Palpation of the dorsal spinous process of the L7 vertebra and dorsoiliac wings. (c) Inset:
a
: epidural space with fat and connective tissue,
b
: dura mater,
c
: arachnoid membrane,
d
: spinal cord,
e
: cerebrospinal fluid,
f
: cauda equine,
g
: seventh lumbar (L7) vertebra,
h
: first sacral (S1) vertebra,
i
: intervertebral disc,
j
: interarcuate ligament (ligamentum flavum), and
k
: interspinous ligament.
Chapter 28: Anesthetic Considerations for Dental Prophylaxis and Oral Surgery
Figure 28.1 Ventral view of a dog skull showing the infraorbital canal and pterygopalatine fossa.
Figure 28.2 Lateral view of a dog skull showing the infraorbital canal. The middle mental foramen is also depicted in this figure.
Figure 28.3 Ventral view of a dog skull showing the major palatine foramen.
Chapter 30: Anesthetic Considerations for Ocular Disease
Figure 30.1 Retrobulbar injection of 5% bupivacaine in an anesthetized dog. The slightly bent 2.5-in spinal needle is inserted over the orbital rim ventral to the eye. Aspirate before injection to confirm the absence of blood. Inject slowly. Slight protrusion of the globe will occur as local anesthetic is injected. Pupillary dilation will occur as the local anesthetic begins to take effect.
Chapter 43: Anesthetic Management of Rabbits and Ferrets
Figure 43.1 Catheter placement in the marginal ear vein of a rabbit.
Figure 43.2 Blind intubation in a rabbit using a capnometer to assist placement.
Chapter 44: Anesthetic Management of Birds
Figure 44.1 Endotracheal intubation in an eagle. Note the obvious airway opening at the base of the tongue. Courtesy of C. Mans.
Figure 44.2 Air sac cannulation of the caudal thoracic air sac in an African grey parrot. Courtesy of C Mans.
Figure 44.3 IV catheter placement in the medial metatarsal vein in an African grey parrot. Also shows toe placement of a pulse oximeter probe. Courtesy of C. Mans.
Figure 44.4 Intraosseous catheter placement in the proximal tibiotarsus of an African grey parrot. Also shows placement of the Doppler crystal over the brachial artery. Courtesy of C. Mans.
List of Tables
Chapter 1: Patient Evaluation
Table 1.1 ASA status categories with descriptions and clinical examples.
Chapter 4: Anesthetic Machine and Equipment Check
Table 4.1 Pre-anesthesia equipment check procedure: These procedures should be performed prior to the first anesthetic delivery of the day. *Not all procedures need to be performed prior to each subsequent anesthetic delivery.
Chapter 5: Pre-Anesthetic Sedative Drugs
Table 5.1 Suggested doses for pre-anesthetic sedative drugs.
Chapter 6: Opioids and Nonsteroidal Anti-Inflammatory Drugs
Table 6.1 Various opioid receptor nomenclature schemes.
Table 6.2 Examples of various types of opioids and doses for dogs and cats
Table 6.3 Examples of clinically available NSAIDs for
dogs
a
Table 6.4 Examples of clinically available NSAIDs for
cats
a
Chapter 7: Anticholinergic Drugs
Table 7.1 Suggested doses for atropine and glycopyrrolate in dogs and cats.
Chapter 8: Time to Premedicate
Table 8.1 Spectrum of premedication effects for a healthy dog or cat.
Table 8.2 Summary of premedication choices for dogs and cats.
Chapter 10: Intravenous Anesthetic Induction Drugs
Table 10.1 Suggested doses for IV induction drugs in
healthy
dogs and cats.
Chapter 13: Inhalant Anesthetics
Table 13.1 Vapor pressures and blood-gas solubility of the common inhalants.
Table 13.2 MAC values of the commonly used inhalants for a variety of veterinary species.
Chapter 14: Total Intravenous Anesthesia (TIVA)
Table 14.1 Drugs for induction and maintenance of TIVA.
Table 14.2 Adjuncts for TIVA.
Chapter 17: Troubleshooting Hypotension
Table 17.1 Adjunctive drugs: note different units for different drugs.
Chapter 18: Troubleshooting Hypoxemia
Table 18.1 Examples of the effects of anemia and hypoxemia on total oxygen content.
Table 18.2 Normal blood gas values in the dog and cat breathing room air (F
i
O
2
∼ 21%). However, when breathing ∼100% O
2
(as during anesthesia), PO
2
values in both dogs and cats are expected to approach 500–600 mmHg with ideal gas exchange [8].
Chapter 22: Constant Rate Infusions
Table 22.1 Recommended intravenous loading and infusion rates of drugs administered as analgesics in dogs and cats.
Table 22.2 Recommended intravenous loading and infusion rates of drugs administered to achieve sedation in dogs and cats.
Chapter 23: Loco-Regional Anesthesia
Table 23.1 Local anesthetic drugs, onset time, duration, and toxic doses.
Table 23.2 Various drugs or drug combinations used for epidural anesthesia.
Chapter 25: Recognition and Assessment of Pain in Dogs
Table 25.1 Typical behavioral signs of acute pain in dogs.
Table 25.2 Typical behavioral signs of chronic pain in dogs.
Table 25.3 Examples of owner-based questionnaires used to quantify chronic pain in dogs.
Chapter 26: Recognition and Assessment of Pain in Cats
Table 26.1 Broad categories used for assessment of quality of life in cats with chronic pain.
Chapter 30: Anesthetic Considerations for Ocular Disease
Table 30.1 NMBA drug doses and durations, and reversal agents.
Chapter 31: Anesthetic Considerations for Upper and Lower Respiratory Disease
Table 31.1 Common causes of ventilatory dysfunction.
Chapter 32: Anesthetic Considerations for Cardiovascular Disease
Table 32.1 Examples of different drugs and recommended doses to have available when anesthetizing a patient with cardiac disease.
Chapter 33: Anesthetic Considerations for Gastrointestinal Disease
Table 33.1 Gastrointestinal side effects of some commonly used anesthetic drugs.
Chapter 36: Anesthetic Considerations for Post-Renal Urinary Tract Disease
Table 36.1 Drug doses for anesthetizing cats with urethral obstruction.
Table 36.2 Drug doses for anesthetizing dogs with urinary tract disease.
Chapter 37: Anesthetic Considerations for Endocrine Disease
Table 37.1 Effects of hypothyroidism on various organ systems.
Table 37.2 Effects of hyperthyroidism on various organ systems.
Table 37.3 Effects of hyperadrenocorticism on various organ systems.
Table 37.4 Effects of diabetes mellitus on various organ systems.
Table 37.5 Effects of pheochromocytoma on various organ systems.
Chapter 42: Anesthetic Considerations for Cats
Table 42.1 Sedative and premedication drugs in cats.
Table 42.2 Dosage regimens and routes of administration of opioid analgesics in cats.
Table 42.3 Anesthetic protocols for spay-neuter programs
a
.
Chapter 43: Anesthetic Management of Rabbits and Ferrets
Table 43.1 Normal values for rabbits and ferrets.
Table 43.2 Sedative and analgesic drug doses.
Table 43.3 Emergency drug doses.
Table 43.4 NSAID drug doses.
Chapter 44: Anesthetic Management of Birds
Table 44.1 Sedation and analgesia drug doses [1,6–8].
Table 44.2 Emergency drug doses for birds.
Questions and Answers in Small Animal Anesthesia
Edited by
Lesley J. Smith DVM, DACVAA
Clinical Professor of Anesthesiology, Department of Surgical SciencesSchool of Veterinary Medicine, University of WisconsinMadison, Wisconsin, USA
This edition first published 2016 © 2016 by John Wiley & Sons, Inc.
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Library of Congress Cataloging-in-Publication Data
Questions and answers in small animal anesthesia / [edited by] Lesley J. Smith.
p. ; cm.
Includes bibliographical references and index.
ISBN 978-1-118-91283-6 (paper)
I. Smith, Lesley J., 1962- , editor.
[DNLM: 1. Anesthesia–veterinary–Problems and Exercises. 2. Analgesia–veterinary–Problems and Exercises. 3. Anesthetics–therapeutic use–Problems and Exercises. SF 914]
SF914.Q47 2015
636.089′796–dc23
2015018227
A catalogue record for this book is available from the British Library.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.
This book is dedicated to the many veterinary patients and students that have taught me so much over the years about anesthesia and about how to teach it. It is also dedicated to my husband and companion animals, who remind me on a daily basis why I do what I do, and how important these creatures are in our lives.
List of Contributors
Richard M. Bednarski, DVM, MSc, DACVAA
Professor, Veterinary Anesthesiology, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, USA
Javier Benito, LV, MS
Resident in Veterinary Anesthesiology, Département de Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, Canada
Benjamin M. Brainard VMD, DACVAA, DACVECC
Associate Professor, Critical Care, College of Veterinary Medicine, University of Georgia, USA
Andrew Claude DVM, DACVAA
Assistant Professor and Service Chief, Anesthesiology, Mississippi State University College of Veterinary Medicine, USA
Tanya Duke-Novakovski BVetMed, MSc, DVA, DACVAA, DECVAA
Professor of Veterinary Anesthesiology, Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Canada
Berit L. Fischer DVM, DACVAA, CCRP
Anesthesia Director, Animal Medical Center, New York City, USA
Stephen A. Greene DVM, MS, DACVAA
Professor of Anesthesia & Analgesia, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, USA
Tamara Grubb DVM, PhD, DACVAA
Assistant Clinical Professor of Anesthesia & Analgesia, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, USA
Rebecca A. Johnson DVM, PhD, DACVAA
Clinical Associate Professor of Anesthesia and Pain Management, Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, USA
Martin J. Kennedy DVM
Anesthesiologist, MedVet Animal Medical and Cancer Center for Pets, Ohio, USA
Carolyn Kerr DVM, DVSc, PhD, DACVAA
Professor of Anesthesiology and Department Chair Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Canada
Katrina Lafferty BFA, CVT, VTS (Anesthesia)
Senior Technician, Section of Anesthesia and Pain Management, Director, Veterinary Technician Student Internship Program, University of Wisconsin-Madison, USA
Lydia Love DVM, DACVAA
Anesthesia Director, Animal Emergency & Referral Associates, USA
Beatriz Monteiro DVM
Département de Biomédecine Vétérinaire, Faculté de Médecine Vétérinaire, Université de Montréal, Canada
Jo Murrell BVSc, PhD, DECVAA
School of Veterinary Sciences, University of Bristol, UK
Odette O DVM, DACVAA
Assistant Professor of Anesthesiology, Ross University School of Veterinary Medicine, St. Kitts
Lysa Pam Posner DVM, DACVAA
North Carolina State University, USA
Jane Quandt DVM, MS, DACVAA, DACVECC
Associate Professor Comparative Anesthesiology, College of Veterinary Medicine, University of Georgia, USA
Gregg S. Rapoport DVM, DACVIM (Cardiology)
Assistant Professor, Cardiology College of Veterinary Medicine, University of Georgia, USA
Carrie Schroeder DVM, DACVAA
Clinical Instructor, Department of Surgical Science University of Wisconsin School of Veterinary Medicine, USA
Andre C. Shih DVM DACVAA
Associate Professor Anesthesia, University of Florida, College Veterinary Medicine, USA
Lesley J. Smith DVM, DACVAA
Clinical Professor of Anesthesiology, Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, USA
Jason W. Soukup, DVM, DAVDC
Clinical Associate Professor, Dentistry and Oral Surgery Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, USA
Paulo Steagall MV, Ms, PhD, DACVAA
Assistant Professor in Veterinary Anesthesiology Département de Sciences Cliniques, Faculté de Médecine Vétérinaire, Université de Montréal, Canada
Ann B. Weil MS, DVM, DACVAA
Clinical Professor of Anesthesiology, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, USA
Erin Wendt-Hornickle DVM, DACVAA
Assistant Clinical Professor, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, USA
Preface
This book is intended to be a practical tool to guide veterinary practitioners, technicians, and veterinary students in the anesthetic management of small animal patients. It is constructed as a step-by-step text that starts at patient evaluation, and then takes the reader through preparation for anesthesia, premedication, induction, maintenance, monitoring and troubleshooting, recovery, and pain management. The book finishes by addressing anesthetic management for specific disease conditions in dogs and cats, breed considerations in dogs, anesthetic specifics in cats, and anesthetic management of small pocket pets and birds. My hope is that it will be a go-to source for anesthesia and analgesia questions that arise on an everyday basis.
Chapter 1Patient Evaluation
Prevention is the Best Medicine!
Lesley J. Smith
Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, USA
Key Points:
A thorough physical exam should be performed on all patients unless it causes undue stress to the patient or is dangerous to the anesthetist.
An overall impression of health, temperament, and body condition score are important to assess in every patient in order to plan drug protocols and doses.
The physical exam should focus on the cardiovascular and respiratory systems, most importantly.
Basic blood work for every patient should include a PCV and TP
Many other additional tests may be indicated depending on the patient's health status and reasons for anesthesia.
Q. Why is it important to perform a complete patient evaluation?
A. Almost without exception, all anesthetic and analgesic drugs have potential toxic effects on organ systems. For example, the inhalant anesthetics significantly decrease blood pressure and organ perfusion such that an animal with pre-existing renal compromise may suffer irreversible renal damage if inhalants are used without monitoring and support of blood pressure. This damage may be even worse if nonsteroidal anti-inflammatory drugs (NSAIDs) are used prior to or during anesthesia.
A complete patient evaluation allows the veterinarian to identify potential health concerns and temperament issues that will affect how that animal responds to the various anesthetic drugs that may be used. In some cases, it may be important to avoid certain anesthetic or analgesic drugs because of identified health concerns. Often many, if not most, anesthetic drugs can be used in patients with significant health problems, but the dose of those drugs may need to be adjusted to minimize known side effects that may be harmful to that particular patient. To continue with the example provided above, in a patient with renal disease inhalants can still be used to maintain anesthesia, but the dose of those inhalants should be kept as low as possible to minimize their negative effects on blood pressure and renal perfusion. Keeping the inhalant dose very low can be achieved by adding other anesthetic or analgesic drugs to the anesthetic protocol, as will be covered in depth in later chapters.
Q. Under what circumstances may patient evaluation be less than complete?
A. Occasionally a patient may be simply too aggressive or unhandled to allow for any physical examination to be conducted safely. Some animals, for example birds, may undergo significant stress from excessive handling and will benefit from a more limited physical examination. Even under these circumstances, however, careful observation “from a distance” can provide important information such as body condition (obese, thin, or just right?), haircoat and general appearance of health, posture and gait (normal or abnormal?), respiratory pattern and effort.
Q. What important questions should I ask the owner when taking a history?
A. The owner may volunteer a lot of information in the history that is or isn't relevant to anesthesia. Some questions that should be asked include:
Has your pet had anesthesia previously and how was his/her recovery at home? – This may alert you to risks of prolonged effects of sedative or other drugs used in the anesthetic protocol.
Are you aware of any problems that your pet had with anesthesia in the past? – Often owners will not know, or will be unsure of, which anesthetic drugs were used previously, but if they recall a specific event (e.g., the vet said he/she had a rough recovery) this can alert you to potential drugs to avoid or to use (e.g., perhaps the rough recovery was because the dog experienced emergence delirium, so this time a longer acting sedative may be indicated).
Are you aware of any relatives of your pet that have experienced complications with anesthesia? – For example, herding breeds of dogs may experience prolonged and profound sedation from certain sedatives and opioids.
Is your pet allergic to any foods or medications that you know of? – Clearly, known allergies to certain medications would indicate that those medications, or ones that are in the same class, should be avoided. Rarely, dogs will have an allergy to eggs, which would make propofol contra-indicated, as propofol contains egg lecithin.
How is your pet's general energy level? Does he/she tire easily or get out of breath quickly during exercise? – Exercise intolerance is a red flag to be on the lookout for cardiovascular or respiratory disease, anemia, or endocrine disease!
Are there any recent changes in drinking or urination habits? – Increases in frequency of water intake should put you on the medical hunt for diseases that cause PU/PD, such as renal disease or diabetes.
Has there been any weight loss or gain that you've noticed recently? – Again if these cannot be explained by a diet change or lifestyle change, then you should be on the hunt for underlying medical issues that could lead to weight gain or loss (e.g., thyroid disorders).
What medications is your pet currently taking? What about nutraceuticals or herbal remedies? – Some medications can directly and significantly impact how the animal responds to anesthetics. For example, ACE inhibitors (e.g., enalapril) can lead to low blood pressure under anesthesia that is unresponsive to most normal interventions.
Q. What are important considerations to look for on initial patient evaluation?
A. The initial patient assessment, before beginning the physical exam, can give you a lot of information. Make a note of the breed, as some breeds warrant special management considerations. Make a note of the animal's temperament: are they quiet, calm, lethargic? If so, then sedative drug doses may need to be reduced. Conversely, are they anxious? Then sedative drugs that provide anxiolysis may be indicated (e.g., acepromazine, midazolam). Are they aggressive and/or dangerous to handle? Then you may need to plan for heavy premedication with drugs that render the animal extremely sedate if not lightly anesthetized. If the dog is athletic and “works for a living” then it may have a normally low resting heart rate, which will be reflected in their heart rate under anesthesia. If that heart rate is normal for them, then you may not need to treat it, even if you consider it bradycardic by most standards.
Also make note of the animal's general appearance of wellbeing. Is their hair coat glossy and clean, or does it have a rough, dry, unkempt, or ungroomed appearance, which may indicate underlying disease, poor nutrition, or lack of self-grooming secondary to disease, stress, or pain.
Lastly, but importantly, assess the animal's body condition. Ideally you will obtain an accurate body weight during your physical, but prior to that, get an impression of whether the animal is close to an ideal weight or not. Obese patients will not breathe well under anesthesia because abdominal and thoracic fat increase the work of breathing and limit thoracic compliance. You should plan to assist ventilation in these patients. Also, drug dose calculations should be adjusted for ideal or lean body weight, otherwise you will be giving a relative overdose of anesthetic drugs. All anesthetic drugs circulate first to organs that receive a high percentage of cardiac output, and because adipose tissue receives very little blood flow, the relative concentration of drugs in the more vascular tissues will be too high if the drug dose is administered based on the obese body weight.
If an animal is too thin, drug doses should be calculated based on the actual body weight. A thin animal, however, may get colder sooner during anesthesia because of the lack of insulating fat.
Q. How should I estimate the patient's ideal weight?
A. Recent studies have reported that ∼40% of dogs in the USA and other countries are overweight and between 5–20% are obese [1, 2]. A commonly used body condition scoring system uses a subjective 9-point scale, where 1 is a morbidly thin animal and 9 is a morbidly obese animal, with a spectrum of body conditions ranked on the scale between these extremes [3]. This system is validated for dogs with < 45% body fat, so may not accurately identify dogs that are extremely obese, which is becoming a more common finding.
A subjective but common-sense approach to estimating ideal weight is to consider the species, breed, and age of the animal and assign a body weight that would be typical for that animal if it had a body condition score of 5–6 (ideal). For example, a typical adult yellow Labrador of average size should weigh approximately 30–33 kg.
Q. What are general considerations for very young or geriatric patients?
A. Very young patients (i.e., less than 5 months of age) have immature liver function [4]. This means that they are slower to metabolize many drugs and are not very efficient at gluconeogenesis, so glucose should be checked and monitored during anesthesia, with supplementation if needed. When glucose falls below 60 g/dl, adding enough dextrose to make a 2.5% (25 mg/ml) solution of dextrose in a balance electrolyte fluid, for example plasmalyte-R, with fluids run at normal anesthetic maintenance rates (see
Chapter 9
: Fluid Therapy), will maintain normal glucose levels.
Geriatric patients should be carefully screened for diseases common to older animals, such as cardiac, renal, hepatic, CNS, and neoplastic disease. As a general rule, doses of sedative drugs should be tapered down in geriatric animals because of delayed clearance. Anesthetic monitoring should also be vigilant in order to quickly address complications that may compromise organ function, such as hypoxemia, hypotension, hypercapnia, and hypothermia. Underlying arthritis should be considered when positioning the patient for procedures, with attention to padding and positioning joints carefully to minimize patient discomfort or stiffness after recovery from anesthesia.
Q. What are the key organ systems to focus on during my physical examination that are relevant to anesthetic planning?
A. The most important organ systems with respect to anesthesia are the cardiovascular and respiratory systems. This is because so many of the negative effects of anesthetic drugs are cardiac and respiratory. A good grasp of abnormalities in these two systems in any given patient will allow for pre-emptive planning in advance in order to minimize anesthetic risk.
The chapters on anesthetic management for cardiovascular and respiratory disease will provide guidelines for how to plan anesthesia for patients where abnormalities in these organ systems exist. With respect to physical examination, the following checklist may help:
Mucous membrane color should be pink.
Mucous membranes should be wet/moist with a capillary refill time of <2 s.
Hydration status should appear normal.
Heart rate should be “normal” for this species and breed.
Are there any murmurs heard? Any arrhythmias?
Are there strong peripheral pulses and are they synchronous with the heart beats?
Is respiratory effort minimal? Does the animal “work to breathe”?
Is there good airflow through both nostrils when the mouth is held shut?
Are normal breath sounds heard in all four lung fields?
Q. Are there any other organ systems I should examine?
A. The abdomen should be gently palpated to search for organomegaly or effusion, both of which can signal neoplastic, hepatic, or cardiac disease. A basic evaluation of CNS function should check that the patient has normal mentation, normal visual reflexes, and responds to voice. Check that the mouth can be easily opened so that intubation will be easy. If not (e.g., mandibular myopathy), you may need to be prepared with an endoscope to visualize the larynx or, worst case, for a tracheostomy.
Q. What bloodwork is important for a young, healthy animal?
A. A suggested minimum data base for a healthy animal should be packed cell volume (PCV) and total protein concentration. These tests are inexpensive and easy to perform and provide a lot of information. PCV will alert you to dehydration (if high) or to anemia (if low), which compromises oxygen carrying capacity and oxygen delivery to tissues. A PCV < 25%, if an acute decrease, should be addressed prior to anesthesia with blood products (packed RBCs, whole blood). Total protein concentration also can indicate dehydration (if high) or a chronic inflammatory disease (if high, because of increases in gamma globulins). Low total protein concentration can indicate poor liver function (e.g., portosytemic shunt) and makes the animal more at risk for hypotension because of low plasma oncotic pressure (fluids will not stay in the vascular space). Coagulation factors may also be low if liver function is poor, so the animal will be at a higher risk for surgical blood loss, even in routine procedures such ovariohysterectomy. Low total protein concentration may also indicate protein loss, for example, from protein-losing nephropathy or GI losses.
In young animals, a baseline blood glucose concentration can be important for making decisions about fluid therapy and glucose support. A reagent test strip, for example Azostix, can provide a rough indication of normal or high blood urea nitrogen concentration, which can clue you in to pre-renal dehydration or renal dysfunction. If high, obtaining a urine specific gravity, also easy to perform, will help determine the animal's concentrating ability and distinguish between pre-renal and renal azotemia.
Q. When should I consider performing more blood work? What tests are most important for anesthesia?
A. A retrospective evaluation of canine patient pre-anesthetic records was performed in order to determine the necessity of pre-anesthetic blood screening. Pre-anesthetic blood work was deemed to be unnecessary in 84% of these patients, as it did not alter the anesthetic plan. Less than 1% of patients required alterations of the anesthetic plan based upon blood work [5]. It is important to note that the majority of these patients were classified as ASA I or II. In a separate study evaluating geriatric canine patients (>7 years), pre-anesthetic blood work resulted in a new diagnosis of subclinical disease in roughly 30% of patients [6]. The results of these studies suggest that pre-anesthetic hematologic and biochemical screening is of value in detecting subclinical disease, especially among geriatric patients, but may not be necessary in all patients. Any patient with significant uncompensated or compensated systemic disease, a history of trauma, urinary obstruction, sepsis, and so on, should have a full CBC and serum biochemical profile with electrolytes. Again, this helps in stabilizing the patient prior to anesthesia and in making decisions regarding fluid therapy, as well as interpreting and managing complications that may arise under anesthesia (e.g., arrhythmias associated with K
+
disorders).
Q. Are there other diagnostic tests that should be considered?
A. Thoracic radiographs should probably be taken in any patient in which a previously undiagnosed heart murmur is heard or in a patient with a history of heart disease that is/is not being treated with medications, in order to assess heart size and the possible presence of heart failure. Patients with a history of trauma often have abnormalities on thoracic radiographs (e.g., pulmonary contusions, pneumothorax). Any patient in which lower respiratory abnormalities are ausculted on physical exam should have thoracic radiographs.
Echocardiography can be useful in identifying the significance of murmurs and assessing cardiac contractility in patients with cardiac disease. Abdominal radiographs, computed tomography, and ultrasound, while not necessarily pertinent to anesthetic planning, can help identify co-morbidities (e.g., metastases) that can change the overall patient plan.
Patients that are suspected to have clotting disorders based on breed (e.g., von Willebrand disease [vWD] in Dobermans), history of disease, or physical exam (e.g., petechiae) should have a platelet count (part of the CBC), buccal mucosal bleeding time (to check platelet function in an animal with a normal platelet count), or PT/aPTT tests, depending on the signs and signalment, to rule out/rule in a bleeding disorder that may increase surgical bleeding and risk. If vWD is suspected, a von Willebrand factor antigen assay should be obtained from a reference laboratory.
Q. What is ASA status and how do I rank a patient?
A. The American Society of Anesthesiologists (ASA) recommends categorizing patients into one of five possible statuses after the patient evaluation has been completed (
www.asahq.org
) [7].
Table 1.1
summarizes the five categories. Any patient that presents as an emergency is ranked at its appropriate status followed by an E. For example, a dachshund with thoracolumbar disc herniation that is otherwise completely healthy, but that requires an emergency hemi-laminectomy would be an ASA 2E.
Table 1.1 ASA status categories with descriptions and clinical examples.
Category
Physical status
Examples
I
normal healthy patient
no signs of obvious disease
II
patient with mild systemic disease
compensated cardiac disease, fracture with no shock
III
patient with severe systemic disease
anemia, moderate dehydration, renal or hepatic disease
IV
patient with severe disease that is life-threatening
uncompensated cardiac disease, renal or hepatic failure, sepsis
V
patient that is not expected to live with or without surgery
profound shock, severe multi-organ failure, severe sepsis, severe trauma
WJ Tranquilli, JC Benson, KA Grimm (eds) Lumb and Jones' Veterinary Anesthesia and Analgesia, 4th edn. Blackwell Publishing: Ames IA, 2007:Table 2.7.
References
1 McGreevy PD, Thomson RM, Mellor DJ,
et al
. Prevalence of obesity in dogs examined by Australian veterinary practices and the risk factors involved.
Veterinary Record
2005;
156
:695–702.
2 Lund EM, Armstrong PJ, Kirk CA,
et al
. Prevalence and risk factors for obesity in adult dogs from private US veterinary practices.
International Journal Applied Research Veterinary Medicine
2006;
4
:177–186.
3 LaFlamme D. Development and validation of a body condition score system for dogs.
Canine Practice
1997;
22(
4
)
:10–15.
4 Root-Kustritz MV. What are normal physical exam findings at various ages in puppies and kittens? In: Root-Kustritz MV (ed.)
Clinical Canine and Feline Reproduction: Evidence-based Answers
, 1st edn. Wiley-Blackwell Publishers: Ames, IA, 2010:278.
5 Alef M, von Praun, F, and Oechtering G. Is routine pre-anaesthetic haematological and biochemical screening justified in dogs?
Veterinary Anaesthesia and Analgesia
2008;
35
:132–140.
6 Joubert KE. Pre-anesthetic screening of geriatric dogs.
Journal South African Veterinary Association
2007;
78
:31–35.
7 American Society of Anesthesiologists.
ASA Physical Status Classification System
.
https://www.asahq.org/For-Members/Clinical-Information/ASA-Physical-Status-Classification-System.aspx
(accessed June 1, 2014).
Chapter 2Owner Concerns
Be prepared with answers
Lesley J. Smith
Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, USA
Key Points:
Trained personnel dedicated to anesthetic monitoring will address many owner concerns about anesthetic risk.
Good monitoring (hands-on, temperature, pulse oximetry, blood pressure, ECG, and capnography) will address owner concerns about anesthetic risk.
Owners should be prepared that their pet may not be “normal” for several days after anesthesia, even if everything goes exactly according to plan.
The following are questions that a pet owner may ask, with possible scenarios or answers that you may provide, depending on your practice. Some questions are taken from the American College of Veterinary Dentistry website [1].
Q. Who monitors the anesthesia at your practice?
A. Responses here could vary from (i) A board certified veterinary anesthesiologist (i.e., a diplomate of the American College of Veterinary Anesthesia and Analgesia). (ii) A veterinarian with some additional training in anesthesia but who is not a diplomate of the ACVAA. (iii) A veterinarian with no additional training in anesthesia post-graduation. (iv) A dedicated veterinary technician with special training in anesthesia (i.e., a veterinary technician with a certificate of Veterinary Technician Specialist – Anesthesia). (v) A dedicated veterinary technician without special training in anesthesia. (vi) A veterinary technician who also helps with the procedure at the same time. (vii) Kennel staff, office staff, volunteer.
A veterinarian should always be involved in choosing anesthetic drug protocols and doses, even if those are standard protocols that have been established by the practice. The American Animal Hospital Association (AAHA) recommends that all animal anesthetics be monitored by a dedicated individual [2]. Clearly, owners who ask this question will be reassured if they know that their pet's anesthesia will be monitored closely, minute to minute, by a trained individual.
Q. What things do you monitor as standard protocol for your anesthesia?
A. This again can run the gamut of possibilities based on the practice type. Minimal monitoring should be hands-on assessment of depth, membrane color, heart rate and breathing, and temperature. AAHA guidelines indicate that minimal anesthetic monitoring include heart rate and rhythm, membrane color, respiratory rate, pulse oximetry, blood pressure, and temperature [3].
Q. Do you keep an anesthetic record?
A. The anesthetic record should be considered a legal document, because if there are any complications related to that pet and the owner pursues it either legally or via the state licensing office, the absence of an anesthetic record will make defense of any actions taken during the anesthetic period very difficult.
Q. What blood work will you perform on my pet?
A. Answers will depend on what is indicated based on the pet's medical condition, reason for anesthesia, age, overall health status, history, and physical exam findings. A minimum amount of blood work for any animal should be a PCV and TP, even if it is obtained after anesthetic induction to reduce patient stress. See
Chapter 1
for other guidelines on pre-anesthetic blood work.
Q. What are the risks of anesthesia?
A. Owners should understand that anesthesia is a risk, for any animal, under any circumstances. Risk can be reduced by careful patient evaluation and anesthetic planning, dedicated anesthesia personnel who monitor the patient on a continuous basis through recovery, and good knowledge of trouble-shooting.
Some potential, but hopefully rare, anesthetic risks that should be shared with owners include: anesthetic death, aspiration and pneumonia, regurgitation with subsequent esophageal ulceration or stricture, delayed/prolonged recovery, post-operative pain/discomfort, CNS abnormalities (blindness, confusion), renal failure, worsening of chronic disease such as cardiac or renal disease.
Q. How will you manage my pet's pain?
A. Many owners do not ask this question, as they assume that their pet's pain will be managed much like their own would be in a hospital setting. They should understand that pain medications may cause some sedation lasting into the time the pet arrives home (e.g., opioids) or may cause other abnormalities in behavior if they are prescribed for at-home administration (e.g., sedation from a fentanyl patch, tremors/agitation from tramadol). The NSAIDs are commonly prescribed for post-operative at-home administration and owners should know that some of these drugs have been associated with (rare) hepatotoxicity (e.g., carprofen) and can worsen renal function in geriatric dogs and, particularly, in cats when they are given for prolonged periods or at high doses. These drugs also can cause GI upset, nausea, melena, diarrhea, and GI ulcers, so owners should be advised of these risks as well.
Q. Why does my pet need an IV catheter? I don't want him shaved!
A. An IV catheter is vital for safe anesthetic induction, administration of IV fluids which help to maintain water balance and blood pressure during anesthesia, and for quick delivery of any emergency or pain drugs we might have to use. Only a small square of hair needs to be shaved in order to place a clean IV catheter. The medial saphenous vein can often be used and is relatively “hidden” compared to the cephalic or lateral saphenous locations.
Q. Why does my pet need anesthesia when I don't need it for the same sort of procedure?
A. Pets will not voluntarily hold still for many relatively non-invasive routine preventative procedures such as dental cleanings. Physical restraint for any length of time is stressful to the pet and potentially painful as well. General anesthesia allows us to complete the procedure more efficiently without the pet feeling any pain or stress during the procedure.
References
1 American College of Veterinary Dentistry.
Questions to ask your veterinarian about your pet's dental cleaning
.
www.acvd.org
(accessed November 12, 2014)
2 American Animal Hospital Association.
AAHA accreditation standards require anesthesia monitoring equipment for your pet's safety
.
www.aahanet.org/Accreditation/aspx
(accessed November 12, 2014)
3 Bednarski R, Grimm K, Harvey R,
et al
. AAHA Anesthesia guidelines for dogs and cats.
Journal of the American Animal Hospital Association
2011;
47
:377–385.
Chapter 3Patient Preparation
They should be prepared too!
Carrie Schroeder
Department of Surgical Science, University of Wisconsin School of Veterinary Medicine, USA
Key Points:
Healthy adult patients should be fasted 8–12 h prior to anesthesia, although water may be offered until the time of sedation.
Fasting time may need to be modified in patients that cannot maintain normoglycemia.
Fasting should not be for more than a few hours in neonates.
Depending on the patient's history, physical examination, and anticipated surgical procedure, pre-anesthetic medications or fluids may be indicated.
Most medications may be administered until the time of anesthesia. However, certain medications may interfere with anesthetic management or may interact adversely with anesthetic agents.
For patients receiving medications prior to anesthesia, it is important to verify potential adverse effects or adverse interactions of those medications with anesthetics that may be used.
Q. For how long should a patient be fasted prior to anesthesia?
A. Pre-anesthetic fasting is important in order to decrease the volume of gastric contents as well as decrease the risk of peri-operative regurgitation. It is generally recommended that adult patients be fasted for 8–12 h prior to the administration of anesthetic medications. Most patients will have adequate glycogen stores and can maintain blood glucose throughout this fasting period. Water may be offered until the time any anesthetic or sedative agents are administered.
Q. Are there exceptions to this rule of thumb in patients with diseases like diabetes or portosystemic shunts?
A. There are certain disease states in which an animal's blood glucose cannot be maintained during fasting. Patients with a diminished capacity to maintain normoglycemia, such as those with portosystemic shunt, should be fasted for a shorter period of time based upon their blood glucose. Generally, these patients should be able to tolerate 4–6 h of fasting. Blood glucose should be checked to verify normoglycemia at the time of induction, sooner if the patient has historically been unable to maintain blood glucose within a normal range. Intravenous glucose supplementation (2.5–5% dextrose) should be performed as necessary.
In patients with diabetes, pre-anesthetic fasting should be undertaken with caution as the patient's insulin dose is typically administered along with food to prevent hypoglycemic episodes. Ideally, surgical procedures should be performed first thing in the morning so that post-operative patients may be monitored closely for the duration of the day and restarted on a regular feeding schedule. Opinions vary on the ideal way to manage blood glucose in diabetic patients, but a common approach is an overnight fast, roughly 6–8 h, followed by administration of one-half the usual insulin dose in the morning. Blood glucose should be monitored every hour following administration of insulin until the time of anesthetic induction, with intravenous glucose supplementation administered as necessary.
Q. For how long should a young animal be fasted?
A. Young animals (< 12 weeks) or species with a high metabolism, such as small birds, rodents, and rabbits, should not have food withheld for more than 2–4 h. These patients may become significantly hypoglycemic if fasted for prolonged periods of time. Neonatal patients (< 4 weeks) should be allowed to nurse from the mother until the time of anesthesia.
Q. What medications should be given prior to anesthesia or anesthetic premedication?
A. There is no standard recommendation regarding the timing and type of medications that should be administered prior to sedation or anesthetic induction. Common pharmacologic agents administered prior to anesthesia include antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDs), anticholinergics, and antihistamines.
Pre-operative antibiotics such as cefazolin are often administered prior to major orthopedic or soft tissue surgeries. As a general rule, prophylactic antimicrobials should be administered approximately 30–60 min prior to the initial surgical incision [1, 2].
Nonsteroidal anti-inflammatory drugs (NSAIDs) are a highly effective component of a multimodal analgesic plan and are most effective when administered prior to the surgical insult [3, 4]. For maximum analgesic effect, NSAIDs should be given at least 30 min prior to surgery. One must use caution in administering these agents in patients with pre-existing hepatic, gastrointestinal, or renal disease or in patients where peri-operative hypotension is anticipated, as hypotension under anesthesia combined with an NSAID “on board” can lead to renal failure [5].
Antihistamines, such as diphenhydramine, and H2-blockers, such as famotidine, are indicated in patients with mast cell tumors to attenuate the negative effects associated with histamine release that may occur with tumor manipulation. It is important that these agents be administered prior to anesthesia in case of mast cell degranulation. These agents should be given roughly 20 min prior to anesthetic induction and can be administered at the time of intramuscular sedation.
Q. What are indications for the administration of pre-anesthetic fluids?
A. While intra-operative fluids are recommended in nearly all patients, the administration of pre-anesthetic intravenous fluids is recommended in selective cases. Patients presenting with renal disease, dehydration, electrolyte abnormalities, and hypovolemic shock are candidates for the administration of pre-anesthetic fluids.
Patients with renal disease, discussed in Chapter 35, should ideally be admitted for intravenous fluid therapy roughly 12–24 h prior to induction of anesthesia. This will allow for stabilization of any possible electrolyte imbalances, correction of dehydration, and optimization of intravenous fluid volume, improving the glomerular filtration rate under anesthesia. Fluid rate should be tailored to each individual patient, based upon the level of dehydration and any concurrent conditions, such as cardiac disease. Patients with renal disease who present on an emergency basis should, at minimum, be administered fluids to replace fluid deficits.
Patients presenting with hypovolemic shock (e.g., gastric dilatation/volvulus), should have fluids administered prior to anesthesia in order to improve cardiac output and tissue perfusion. Ideally, fluid administration rate and amount should be guided by measurement of the patient's central venous pressure (CVP) in order to prevent fluid overload. In the absence of CVP measurement, patient response to fluid administration can be gauged by pulse rate and quality, capillary refill time, auscultation of lung sounds, and respiratory rate and effort.
Q. How can I calculate the rate of administration of pre-anesthetic fluids?
A. The rate of fluid administration for patients with dehydration can be calculated based upon maintenance fluid need (40–60 ml/kg/day or 1.7–2.5 ml/kg/h) plus replacement of any fluid deficit, in addition to fluids to account for ongoing losses such as vomiting, if present. This can be estimated by assessing the patient's level of dehydration and replacing the deficit over 4–6 h or longer if time allows.
For example, a 5 kg patient presenting with 7% dehydration should have an initial fluid rate calculated as:
Following correction of dehydration, the rate of administration should be at least the maintenance fluid rate until the time of anesthesia.
Q. I have a patient with heart disease who is on a lot of medications. Should I continue those up to the time of anesthesia? All of them or just some?
A. It is common for patients with cardiovascular disease to require a number of medications, including beta blockers (e.g., atenolol), calcium channel blockers (e.g., amlodipine), angiotensin-converting enzyme inhibitors (ACEIs) (e.g., enalapril), and the phosphodiesterase inhibitor pimobendan. Patients presenting with chronic therapy of these medications often have a finely tuned regimen and it is important to avoid disruption of the homeostasis of therapy. However, refractory hypotension can occur upon concurrent administration of anesthetic agents such as propofol and volatile anesthetics with ACEIs [[6–8]]. Therefore, it is important that ACEI therapy be temporarily discontinued for 24 h prior to anesthetic induction, unless the ACEI is administered to treat hypertension. All other cardiac medications may be continued as usual. It is important, however, to be aware that patients treated with beta-blockers may be bradycardic and require anticholinergic therapy.
Q. What other types of diseases and/or medications should be continued up to the time of anesthesia?
A. Most medications may be continued until the time of anesthesia, especially those administered to treat chronic conditions. This includes treatments for mast cell tumor, epilepsy, hyper- and hypothyroidism, hyper- and hypo-adrenocorticism, and most cardiac medications, as described previously. It is, however, very important to check for possible reactions with anesthetic agents prior to formulating an anesthetic plan. Fortunately, cross-reactions with anesthetics and other pharmacologic agents are relatively rare but untoward reactions have been known to occur. It is far more common to have additive pharmacologic effects, such as hypotension or excessive sedation.
Q. When should ongoing medications be discontinued prior to anesthesia and for how long?
A. There is no general rule for discontinuing medications prior to anesthesia; the administration guidelines should be based upon the individual patient, disease condition, anesthetic plan, and therapeutic regimen. As stated previously, it is important to know any potential cross-reactions and adverse effects of any therapeutic agent prior to administration of any anesthetic agent. For example, antidepressants such as selective serotonin reuptake inhibitors (SSRIs) or monoamine oxidase inhibitors (MAOIs) may interact with opioids such as meperidine to cause a relatively rare disorder called serotonin syndrome. More commonly, therapeutic agents may compound the known effects of anesthetic agents such as hypotension or sedation.
