Sunday, January 15, 2006

hyperthermia (fever, sunstroke, heat exhaustion, heatstroke, heat cramps)

Unusually high body temperature is known as hyperthermia. The causes of elevated temperature are exposure to excessive heat, impaired thermoregulatory reflexes, and infections. Dangerous increases in body temperatures are more likely to occur in the elderly. During heat waves they may be unable to lose body heat adequately through sweating and peripheral vasodilatation, thus their temperature rises.
Mortality, from all causes, rises dramatically during heat waves in people over 50 and it progresses with increasing age. Many deaths are attributed to cardiovascular or cerebrovascular disease when, in fact, they can be directly related to a high body temperature. Deaths have occurred when air conditioning has failed or in residences where fans or air conditioning were not available. Older people traveling to unaccustomed hot climates have been susceptible to hyperthermia. Those people with impaired thermoregulatory reflexes have difficulty controlling their body temperature even on exposure to moderate heat. The primary causes are lesions of the hypothalamus, lesions of the spinal cord, and extensive skin lesions. But even in the absence of lesions, the elderly show a higher threshold of elevated temperature and a decrease in sweating. Impaired temperature regulation, from diminished or absent sweating, is probably the main factor in increased mortality in the elderly during heat waves.
Infections cause fever, probably by raising the set point of the temperature-regulating mechanisms. In the elderly, fever gives rise to headache, dizziness, restlessness, and confusion. Delusions, hallucinations, and paranoia may also occur. Dehydration can occur rapidly since the elderly do not exhibit thirst as early as a younger person. Peripheral circulatory failure from sodium and water depletion can occur.
In moderate fever, the use of aspirin and correction of the underlying cause may be all that is necessary, with attention also given to early dehydration. In high fever, as in heatstroke (sunstroke), speed is essential to prevent brain damage. The skin becomes hot, dry, and flushed and body temperature rises to over 104 degrees. Without treatment most heatstroke victims will die. Treatment consists of sponging with cold water or immersion in ice water. Wet blankets and fans, to aid in evaporated cooling, are also effective. The mortality from heatstroke is extremely high in the elderly. If the high temperature continues, serious and permanent brain damage results. Treatment should continue until body temperature is reduced to at least 102 degrees. If the person does not then respond, brain damage may have already occurred. Impairment of consciousness may lead to coma. Cardiac dysrhythmias, pneumonia, purpura, and gastrointestinal bleeding are common with sequelae hyperthermia.
See also HEAT INDEX.
Brocklehurst, J. C. Textbook of Geriatric Medicine and Gerontology 3rd ed. New York: Churchill Livingstone, 1985.
Phipps, W., et al. Medical Surgical Nursing. St. Louis: C. V. Mosby Co., 1983.

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