Induced and accidental hypothermia.

OBJECTIVE To review human thermoregulation and the pathophysiology and management of induced and accidental hypothermia. DATA SOURCES A review of studies reported over ten years from 1990 to 2000 and identified through a MEDLINE search of the English-language literature on thermoregulation and induced and accidental hypothermia. SUMMARY OF REVIEW Hypothermia is defined as a core temperature less than 35 degrees C, and may be therapeutic (i.e. induced for clinical benefit) or accidental. Hypothermia induced prior to cardiovascular or neurosurgical procedures (i.e. therapeutic hypothermia) allows for a greater hypotensive operative period with less risk of cerebral or cardiac ischaemic injury. Hypothermia induced following tissue injury (e.g. closed head injury, cerebrovascular accident, adult respiratory distress syndrome) has also been used to reduce ischaemic tissue injury, although significant clinical benefits have not yet been demonstrated. Inadvertent hypothermia (i.e. accidental hypothermia) is classed as mild from 33 degrees C-35 degrees C, moderate from 30 degrees C-33 degrees C and severe if less than 30 degrees C. Treatment includes surface and core warming methods, all of which have a valid basis from experimental studies. However, no prospective, randomised controlled clinical trials exist that have compared the various rewarming methods. Currently, passive rewarming methods (e.g. reflective metalloplastic sheets, blankets) are recommended for patients with mild hypothermia (> 33 degrees C), active surface rewarming (e.g. heated blankets, hot air circulators) for moderate hypothermia (> 30 degrees C), active core rewarming (e.g. heated haemodialysis, haemodiafiltration or peritoneal dialysis) for severe hypothermia (< 30 degrees C), and heated cardiopulmonary bypass for severe hypothermia with cardiopulmonary arrest. CONCLUSIONS Operative hypothermia reduces ischaemic injury during cardiac and neurosurgical procedures. Hypothermia induced following tissue injury has not yet been shown to be of benefit. Management of accidental hypothermia requires passive and active warming methods, the indication of each depending on the availability of the method and severity of hypothermia.