Hypothermia

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Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Revising Editor: Melissa Conrad Stöppler, MD

• What is hypothermia?
• What causes hypothermia?
• What are the risk factors for hypothermia?
• What are the signs and symptoms of hypothermia?
• How is hypothermia diagnosed?
• How is hypothermia treated?
• When should I call the doctor for hypothermia?
• Can hypothermia be prevented?
• Hypothermia At A Glance

What is hypothermia?

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.