Questions and Answers in Small Animal Anesthesia

Lesley J. Smith

• Publisher: Wiley-Blackwell
• Year: 2015
• Print ISBN: 9781118912836
• eBook ISBN: 9781118912935
• Edition: 1
• Topic: Medicine
• Subtopic: Veterinary Medicine

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

Chapter 1
Patient Evaluation

Prevention is the Best Medicine!

Lesley J. Smith

Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, USA

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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.

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1. Q. Why is it important to perform a complete patient evaluation?
2. 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.
3. Q. Under what circumstances may patient evaluation be less than complete?
4. 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.
5. Q. What important questions should I ask the owner when taking a history?
6. 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.
7. Q. What are important considerations to look for on initial patient evaluation?
8. 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.
9. Q. How should I estimate the patient's ideal weight?
10. 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.
11. Q. What are general considerations for very young or geriatric patients?
12. 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 l...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Table of Contents
• List of Contributors
• Preface
• Chapter 1: Patient Evaluation
• Chapter 2: Owner Concerns
• Chapter 3: Patient Preparation
• Chapter 4: Anesthetic Machine and Equipment Check
• Chapter 5: Pre-Anesthetic Sedative Drugs
• Chapter 6: Opioids and Nonsteroidal Anti-Inflammatory Drugs
• Chapter 7: Anticholinergic Drugs
• Chapter 8: Time to Premedicate
• Chapter 9: Intravenous Access and Fluid Administration
• Chapter 10: Intravenous Anesthetic Induction Drugs
• Chapter 11: Inhalant Inductions
• Chapter 12: Induction Techniques for the Really Sick Patient
• Chapter 13: Inhalant Anesthetics
• Chapter 14: Total Intravenous Anesthesia (TIVA)
• Chapter 15: Anesthetic Monitoring Basics
• Chapter 16: Normal Values for Anesthetized Patients
• Chapter 17: Troubleshooting Hypotension
• Chapter 18: Troubleshooting Hypoxemia
• Chapter 19: Troubleshooting Hypercapnia and Hypocapnia
• Chapter 20: Troubleshooting Hypothermia and Hyperthermia
• Chapter 21: Common Arrhythmias in Anesthetized Patients
• Chapter 22: Constant Rate Infusions
• Chapter 23: Loco-Regional Anesthesia
• Chapter 24: Troubleshooting Anesthetic Recovery
• Chapter 25: Recognition and Assessment of Pain in Dogs
• Chapter 26: Recognition and Assessment of Pain in Cats
• Chapter 27: Post-Operative Analgesia – Approaches and Options
• Chapter 28: Anesthetic Considerations for Dental Prophylaxis and Oral Surgery
• Chapter 29: Anesthetic Considerations for Neurologic Disease
• Chapter 30: Anesthetic Considerations for Ocular Disease
• Chapter 31: Anesthetic Considerations for Upper and Lower Respiratory Disease
• Chapter 32: Anesthetic Considerations for Cardiovascular Disease
• Chapter 33: Anesthetic Considerations for Gastrointestinal Disease
• Chapter 34: Anesthetic Considerations for Hepatic Disease
• Chapter 35: Anesthetic Considerations for Renal Disease
• Chapter 36: Anesthetic Considerations for Post-Renal Urinary Tract Disease
• Chapter 37: Anesthetic Considerations for Endocrine Disease
• Chapter 38: Anesthetic Considerations for Orthopedic Surgery
• Chapter 39: Anesthetic Management of Common Emergencies in Small Animals
• Chapter 40: Anesthetic Management of Brachycephalic Breeds
• Chapter 41: Anesthetic Considerations for Other Canine Breeds
• Chapter 42: Anesthetic Considerations for Cats
• Chapter 43: Anesthetic Management of Rabbits and Ferrets
• Chapter 44: Anesthetic Management of Birds
• Index
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