Physiology and pharmacology of hypothermia.

Homoiothermic organisms react to hypothermia by shivering and thermogenesis to retain their euthermic state. This reactive homeostatic mechanism recruits a strong sympathetic response, which must be suppressed by anesthesia and adjuvants during induced hypothermia. Below 30 degrees C there is significant neural and organ depression associated with cold narcosis. Cardiac arrhythmias and ventricular fibrillation are grave developments when the core temperature is below 28 degrees C. Proper cardiopulmonary support must be instituted in a patient who has induced or accidental hypothermia at these severely hypothermic levels.Although clinical hypothermia is used to protect the brain and the heart from ischemic insults during an operation, it induces a complex array of physiologic changes in the body that must be appreciated so that optimal care may be provided to a patient.