Today's Veterinary Practice

MAY-JUN 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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70 FOCUS ON PEER REVIEWED REVIEWED PEER Keeping any anesthetized animal from hypothermia before, during, and after surgery is a delicate balance of monitoring during treatment and avoiding potential complications when the animal is recovering. This article provides a case study of a Yorkshire terrier under anesthesia during surgery, along with the pathophysiology of hypotension and methods that can be used to manage it during and after surgery. HYPOTHERMIA UNDER ANESTHESIA For any animal under anesthesia for longer than 20 minutes, techniques to minimize heat loss should be applied. 1 This is because detrimental effects, such as a decreased ability to recover and an increased incidence of infection, can occur in instances of severe hypothermia, and in the critical patient this could lead to death. Also hypothermia may persist into recovery and affect recovery quality and duration. Hypothermia can be defined according to the decrease from normal body temperature. Normal body temperature is 37.5˚C to 39.2˚C (99.5˚F to 102.5˚F) for a dog and 37.8˚C to 39.5˚C (100˚F to 103.1˚F) for a cat.2 Mild hypothermia is 37.0˚C to 37.7˚C (98˚F to 99.9˚F); moderate, 35.8˚C to 37.0˚C (96˚F to 98˚F); severe, 33.6˚C to 35.8˚C (92˚F to 96˚F); and critical, less than 33.6˚C (92˚F or less). 3,4 Core temperature changes occur in 3 phases during anesthesia. ■ In the first hour, an initial rapid decline results from peripheral vasodilation and redistribution of body heat. ■ Over the following 2 hours, the temperature declines in a slower linear fashion because of the inhibition of metabolism and heat production by the anesthetic drugs. ■ Finally, over the next 3 to 4 hours, core temperature stabilizes and remains relatively unchanged as thermal steady state is achieved. Body temperature changes in a predictable manner as a result of the core-to-peripheral temperature gradient. 4,5 The gradient is maintained mainly via peripheral vasoconstriction, which keeps the body heat in a central pool of blood and minimizes the heat that can be lost through the skin. 4 The extremities will be cooler because of shunting of blood to the core.1 The size of the animal plays a role in heat loss. A larger body surface area increases these losses through cutaneous loss. That means that small- and toy-breed dogs have a greater risk for heat loss than large-breed dogs because of their higher surface area. Hypothermia in the Operating Room Jane Quandt, DVM, DACVAA, DACVECC University of Georgia College of Veterinary Medicine FOCUS ON shutterstock.com/Igor Normann

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