Hypothermia
Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Revising Editor: Melissa Conrad Stöppler, MD
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.
Next: What causes hypothermia? »
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