Hypothermia

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Medical Author:

Benjamin Wedro, MD, FACEP, FAAEM

Benjamin Wedro, MD, FACEP, FAAEM

Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

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Medical Editor:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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The body maintains a relatively stable temperature whereby heat production is balanced by heat loss. Normally, the core body temperature (when measured rectally) is 98.6 degrees F or 37 degrees C. When the outside environment gets too cold or the body's heat production decreases, hypothermia occurs (hypo=less + thermia=temperature). Hypothermia is defined as having a core body temperature less than 95 degrees F or 35 degrees C.

Body temperature is controlled in the part of the brain called the hypothalamus, which is responsible for recognizing alterations in the body temperature and responding appropriately. The body produces heat through the metabolic processes in cells that support vital body functions. Most heat is lost at the skin surface by convection, conduction, radiation, and evaporation. If the environment gets colder, the body may need to generate more heat by shivering (increasing muscle activity that promotes heat formation). But if heat loss is greater than the body's ability to make more, then the body's core temperature will fall.

As the temperature falls, the body shunts blood away from the skin and exposure to the elements. Blood flow is increased to the vital organs of the body including the heart, lungs, kidney, and brain. The heart and brain are most sensitive to cold, and the electrical activity in these organs slows in response to cold. If the body temperature continues to decrease, organs begin to fail, and eventually death will occur.

Medical uses of hypothermia

Cooling patients as part of their medical care is called induced or therapeutic hypothermia. While there is potential benefit of this practice for many conditions, at present, medical hypothermia is most often used in patients who have been resuscitated from cardiac arrest.

Medical scientists have shown that in patients who survived episodes of cardiac arrest due to ventricular fibrillation or ventricular tachycardia, cooling the body to 93.2 F (34 C) for 12-24 hours was associated with better survival rates and better neurologic outcomes.