1. Convection: transfer of heat from the body surface to air moving past the animal
2. Conduction: transfer of heat from the body surface to colder objects (e.g., cold table surfaces, cage floors) in contact with the skin
3. Radiation: exchange of heat between the body and objects in the environment that are not in contact with the skin, independent of the temperature of the intervening air
4. Evaporation: occurs when moisture (e.g., surgical preparation solutions) in contact with the skin or respiratory tract dissipates into the air, pulling heat with it

Primary and secondary hypothermia occur during commonly encountered clinical scenarios, including:

• Surgery or general anesthesia
• Trauma
• Hypovolemia
• Environmental exposure

Therapeutic efforts are aimed at rapidly rewarming patients during fluid resuscitation as well as reducing additional heat loss. Resuscitative efforts should not contribute to the hypothermia. Rewarming hypothermic animals can be accomplished by several different methods, including:

• Passive Surface (e.g., blankets)
• Active Surface (e.g., Bair hugger, heated water bed)
• Active Core Rewarming (e.g., peritoneal and pleural lavage)

It has been recommended to warm the animal by at least 1-2 degree Celsius per hour; however, faster rates may be necessary. Moderate intravascular volume support is recommended during active rewarming in hypovolemic shock; this will support mean arterial blood pressure (MAP) and resolve most cases of hypothermia-induced hypotension, bradycardia, hypoventilation, and coagulopathy while avoiding volume overload. Electrolytes and acid-base status should be monitored and alterations addressed. The ECG, MAP, and blood gases should be monitored closely in severely hypothermic patients. Surface rewarming should always accompany active core rewarming to reduce core-to-peripheral temperature gradients. During external heating, care must always be taken to prevent skin burns by controlling the temperature of the external heating devices or placing a barrier between the heat source and the patients.

A patient's core body temperature may continue to drop for a period of time after the onset of rewarming. This condition, referred to as the "afterdrop" is caused by the return of cold peripheral blood to the body core and movement of blood from the warmer core to the periphery. A second important complication to anticipate is the development of rewarming shock. Rapid rewarming will cause a great metabolic burden on patients as well as significant vasodilation that may overwhelm an already compromised circulatory system.