Topics in medicine and surgeryCurrent Techniques in Avian Anesthesia
Section snippets
Cardiorespiratory Physiology
The avian cardiovascular system is considered a “high performance” system. Compared with mammals, birds have a proportionally larger heart, larger stroke volume, greater cardiac output, higher blood pressures, and a lower heart rate.3 An increase in the release of endogenous catecholamines, as it occurs during periods of stress, may have greater impact on birds during anesthesia. Hypoxia, severe hypercapnia, and anesthetic drugs may produce further depression of the cardiovascular system.
Inhaled Anesthetics
Inhalant anesthesia is the preferred method for the induction and maintenance of anesthesia in birds. Advantages of using inhaled anesthetics for these phases include rapid induction and recovery, ability to make rapid and frequent adjustments in anesthetic depth, minimal biotransformation, minimal cardiorespiratory side effects, or organ toxicity at clinically useful doses. These qualities make most inhaled anesthetics ideal for anesthesia of birds with liver- and/or kidney-altered function.
Pre-anesthetic Evaluation of Birds
Ideally, in a scheduled anesthetic procedure, a pre-anesthetic physical examination is completed a day before the procedure. Body weight, baseline vital signs, and diagnostic blood tests (complete blood cell count, hematocrit, total protein, glucose, uric acid, Aspartate Aminotransferase (AST), calcium, phosphorus, and creatine phosphokinase) provide useful information for both drug selection and dosing. In the event that a pre-anesthetic examination is not possible, data can be obtained during
The Anesthetic Period
All phases of anesthesia (premedication, induction, maintenance, and recovery) are critical components of the anesthetic period. Complications can occur during any of these periods, and careful planning and attention to detail throughout the entire perianesthetic period can lower the risk of occurrence of critical incidents that may negatively affect outcome.
Fluid Choice
The choice of fluid type is determined by the status of the patient (packed cell volume (PCV), total protein (TP), dehydration status) and any anticipated or calculated surgical blood loss. Because of the bird’s high metabolic rate and low glycogen-storage capacity, a regular assessment of blood glucose concentration is recommended. This is rarely performed in clinical settings in smaller birds because of their small blood volume. However, glucometers require a very small amount of blood; a
Anesthetic Complications
During the anesthesia of birds, it is prudent to have the more commonly used emergency drugs, such as atropine and epinephrine, drawn up and ready for injection (Table 3).
Respiratory arrest, closely followed by cardiac arrest, is not an infrequent complication associated with avian anesthesia. Respiratory arrest is often reversible when detected early. After recognition of respiratory arrest, the first step in treatment should be either reducing or turning off the inhaled anesthetic and/or
Summary
Despite considerable research into the identification of the ideal injectable anesthetic for birds, inhaled anesthetics remain the most frequently administered drugs for general anesthesia. Inhaled anesthetics are favored because of their relative safety, short onset and duration of action, and comparably smooth and quick recoveries. However, inhalant drugs have no analgesic properties, and appropriate analgesics must be given. Options for pain management are discussed in a separate article in
Acknowledgments
The authors would like to thank Alex Valverde, Jim Wellehan, and Jessica Siegal-Willet for their help with this manuscript and Michelle Mehalick for providing Figure 3.
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