Anesthesia and analgesia for exotic animals (Proceedings)

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Anesthesia and analgesia for exotic animals (Proceedings)

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Aug 01, 2008

Clinicians working with "exotic species" should establish consistent anesthetic and analgesic protocols to manage cases that require diagnostic or surgical procedures. Unfortunately, there are still individuals that attempt to manage these cases using "bruticaine" or hypothermia (e.g., placing reptiles into a refrigerator or freezer). These techniques are not only cruel, but can prove fatal. Advances in domestic animal anesthesiology have provided safer, consistent compounds that may be used to anesthetize exotic species.

A patient should receive a thorough examination, including auscultation of the heart and lung(s), prior to any anesthetic procedure. In those cases where auscultation is limited, such as with reptiles, an ultrasonic doppler may be used to assess the heart. Pre-surgical blood work, which is commonly performed in domestic species, can provide insight into the physiological status of an animal. A complete blood count and plasma chemistry panel should be performed when possible. In cases where blood volume or owner finances are limited, a packed cell volume, total solids, and blood smear can be performed to provide important information regarding the animal's status.

Ectotherms, such as reptiles and amphibians, should be provided supplemental heat during an anesthetic procedure that is consistent with their preferred environmental temperature. Endotherms, including birds and exotic species of mammals, should also be provided supplemental heat during these procedures. Hypothermia in endotherms can result in the loss of essential energy to maintain an appropriate core body temperature. Animals maintained at an inappropriate temperature will experience a prolonged recovery. Water-circulating heat pads and forced air heating units provide good results and are unlikely to cause thermal burns. Radiant heat from an incandescent light can also be used to provide supplemental heat.

Variability in the physiology of exotic species often results in variable responses between classes of animals. For example, anesthetics that provide surgical anesthesia in a mammal or bird may provide little to no anesthesia in a reptile or amphibian. Differences in anesthetic responses within animal classes have also been described. The anesthetic agents that have been found to provide the most reliable results in exotic species include the dissociatives, alpha-2 agonists, propofol, and inhalant anesthetics.

Dissociative agents are routinely used to anesthetize reptiles and rabbits. The most common dissociative agents used for reptile anesthesia are ketamine (Ketaset, Ft. Dodge Laboratories, Ft. Dodge, IA, USA) and tiletamine (Telazol, Fort Dodge Laboratories, Ft. Dodge, IA, USA), while ketamine is the preferred agent for rabbits. Reported dosages for ketamine are quite varied. When a short, painless procedures (e.g., examination) or pre-anesthetic is required (e.g., facilitate intubation) for reptiles, a dose between 10-30 mg/kg IM is sufficient. Ketamine provides minimal analgesia and should be combined with an analgesic when a painful procedure is performed. A dose of 55-88 mg/kg IM has been recommended for surgical anesthesia in reptiles, but ketamine is inappropriate as a sole anesthetic in a surgical procedure. Ketamine is generally used in combination with alpha-2 agonists in rabbits. If used alone, a dose from 15-30 mg/kg may be used, whereas the dose can be reduced when the drug is used in combination with an alpha-2 agonist. Side effects reported with ketamine usage include respiratory arrest, bradycardia, skin depigmentation, and prolonged recoveries. These side effects are usually associated with the administration of high doses (>80 mg/kg). Tiletamine is more potent than ketamine and provides similar results at a lower dose in reptiles (3-8 mg/kg). The addition of zolazepam is of benefit because it improves muscle relaxation and is an anticonvulsant. Tiletamine has been used in snakes, lizards and crocodilians with some success, but recoveries are still prolonged. Tiletamine should only be used for short, painless procedures or as a pre-anesthetic as it provides limited analgesia. The dissociatives have been used in birds, but generally result in violent recoveries.

The alpha-2 agonists, including xylazine and medetomidine, have been used with good success in exotic species. In general, they are used in combination with other drugs. Of the two drugs, medetomidine is used more frequently because of its greater effect and potency in exotic species. Medetomidine provides muscle relaxation, analgesia and is reversible with atipamezole. The primary side effect associated with this drug is cardiopulmonary depression.