Induced hypothermia
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Induced hypothermia is sometimes used as preparation for surgery on the heart or during artificial coma to increase survival chances after cardiac arrest or severe injury.
Hypothermia is also a consequence of anesthetic induction drugs and occurs to some extent every time an anesthetic is given. Anesthetic drugs produce two different effects that lead to hypothermia during surgery: they increase the width of blood vessels, vasodilation, which means that blood flows easily from the body's inner organs or core to the periphery or skin. This allows heat to be easily lost or radiated from the body. The temperature control center situated in hypothalamus is also affected by drugs causing the normal temperature control limits to be increased, compromising the body's normal cold response system.
Research has also shown that in patients who are successfully resuscitated after cardiac arrest (stopping of the heart), but who remain in a comatose state, the chance for recovery is increased if the patient is then mildly cooled to about 33 degrees Celsius (91 °F). The evidence is best for its use in patients who have had a cardiac arrest due to ventricular fibrillation or ventricular tachycardia, although its use is also being expanded to other sorts of rhythms. The prognosis in these patients is very poor but patients who are cooled have better survival rates and better neurological recovery. During the cardiac arrest there is inadequate perfusion of the brain and when circulation is restored brain cells die. Hypothermia is thought to reduce the death of these cells. This is usually accomplished by either ice-cold intravenous fluids, external cooling with ice packs or intravascular cooling. This therapy is increasingly being used in hospital emergency departments and intensive care units.
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