Warming the Hypothermic Canine and Feline Patient
Hypothermia commonly occurs in critically ill or injured canine and feline patients as a result of excessive heat loss, decreased metabolism and/or loss of the ability to thermoregulate at the level of the autonomic nervous system.
Passive external rewarming by covering the patient with a blanket or towel may be sufficient in warming mildly hypothermic patients. This method minimizes heat loss to the surrounding environment and relies on the patient’s own endogenous heat generation to warm the patient. In moderate to severely hypothermic animals, this method is useful in preventing heat loss but is insufficient to warm the patient, as these patients generally have decreased ability to generate their own heat. In these cases, active rewarming methods are used to provide the patient with exogenous heat.
Active external rewarming is most commonly performed in veterinary medicine through the use of forced air (e.g. Bair Hugger), resistive heating (e.g. Hot Dog warming system), hot water bottles, or warm water blanket. Complications may include vasodilation resulting in relative hypovolemia and shock. Return of colder blood and lactic acid from the periphery to the vital organs may also result in drop in core temperature and rewarming acidosis. These effects can be mitigated to some degree by focusing rewarming on the trunk rather than the extremities.
Active core rewarming allows more direct application of exogenous heat to core organs, however this is less commonly used in veterinary medicine. Warmed IV crystalloids may be given but this is not generally effective due to low flow rates. Warmed humidified air may be delivered via face mask or endotracheal tube. Heated peritoneal or thoracic lavage are more invasive methods of active core rewarming and are not commonly performed, but may be useful in dogs and cats experiencing cardiac arrest.
