Perioperative hypothermia is common in small animals undergoing anesthesia. Anesthesia can increase heat loss by 20% to 30%, which is further complicated by heat loss via conduction (e.g., heat from animal's body to surgery table), convection (e.g., heat loss to surrounding air), or evaporation (e.g., loss of heat because of water or alcohol evaporation). Hypothermia is associated with delayed recovery from anesthesia; poor perfusion of body tissues; decreased respiratory rate and tidal volume, predisposing patients to hypoxia, pulmonary edema, acute respiratory distress syndrome, or pneumonia; and depressed mentation in postoperative patients; and it may predispose patients to infection. The best monitoring devices are rectal or esophageal probes. Placing blankets over and beneath patients can prevent hypothermia; blankets have been shown to decrease heat loss by 30%. More active techniques include warming the air around the patient with hot-water bottles, circulating warm-water heating pads, and forced-air warming blankets. A Bair Hugger system is the most effective way to warm the patient's exterior. Loss of core body heat during surgery can be treated or minimized by using warm IV or lavage fluids. The most common complications from rewarming include increased metabolic rate and oxygen consumption, thermal burns, and mild hyperthermia. The best way to avoid burns is to place padding between patient and heating device and to avoid electric heating blankets or pads. Monitoring of body temperature is recommended because some patients experience "afterdrop" hypothermia, during which body temperature continues to decrease because external rewarming causes peripheral vasodilatation and exchange of warmer core blood for cooler peripheral blood. Rewarming shock is another complication caused by rapid vasodilatation secondary to external warming and venous pooling that the circulatory system cannot overcome.

COMMENTARY: Any anesthetized patient is at risk for hypothermia unless the practitioner takes proactive steps. This is a concise article reviewing thermoregulation; the causes of perioperative hypothermia; and current, practical ways to prevent and treat hypothermia. Forced-air warming blankets have become less expensive, and they are becoming the standard of care in veterinary practice, as they are in human medicine. These blankets provide better warming benefits and less risk for thermal injury when used properly.

Perioperative hypothermia. Armstrong SR, Roberts BK, Aronsohn M. J VET EMER CRIT CARE 15:32-37, 2005.