Hyperthermia risk factors in the elderly

The risk of death related to hyperthermia is greatest for the very young and the elderly. Over 600 people die each year in the United States from avoidable exposure to extreme heat. Individuals 65 years of age or older suffer a disproportionate number of these heat related deaths.

As you might expect Arizona has America's highest incidence of heat related deaths. The CDC reports that between the years 1993-2002 Arizona deaths due to heat exposure were 3 to seven times the national average. The vast majority of these deaths occurred in the > 65 year old population. The highest mortality rate occurs during the summer when daily temperature can be over 100 F from June to mid-September. Almost all of these deaths could be avoided if systems were in place to identify and assist high risk individuals.

Other parts of the country may be even less prepared for the sporadic heat waves which occur as part of the normal climatic condition. In more temperate climates where air conditioning is less common the effect of a heat wave can be devastating. A heat wave is a meteorological event defined as >3 consecutive days of air temperatures >90º F. Once again heat related deaths are preventable.

Modern weather forecasting is reasonably able to anticipate a heat wave. It is therefore incumbent upon public health officials to identify susceptible populations and prepare appropriate shelter. Electrical service disruptions resulting from increased load often coincide with extreme heat. Public Health Services should encourage the public check on "at risk" neighbors during such events and provide transport to safe shelter.

The 2003 heat wave in France stands a an unfortunate example of the effects of a sporadic heat wave. In August the average temperature in Paris is about 75ºF and air conditioning is rare. In August 2003, temperatures rose to 104ºF and stayed high for about two weeks. When the heat wave abated it is estimated that as many as 11,000 people died across France, the bulk of which were elderly.

Three mechanisms can lead to hyperthermia. These mechanisms include external heat gain, increased metabolic heat, and impaired heat dissipation. Hot weather can bring these factors together with disasterous consequences for the elderly.

It is important to note that the ambient temperature does not have to reach 100 degrees for elders to be at risk of hyperthermia. External heat gain occurs whenever a person is exposed to an environmental temperature which is greater than the individual's ability to dissipate. Elders often have a decreased ability to dissipate heat. Factors that impair heat dissipation include lack of acclimatization to high temperatures, high humidity, obesity, heavy clothing, cardiovascular disease and dehydration. Studies indicate that the number of sweat glands do not substantially decrease with age but function is reduced. Cutaneous blood flow has been shown to be reduced with age. This is due to a loss of capillary vessels and microcirculation which reduces the ability to radiate excess heat.

The risk that a person will become hyperthermic when exposed to high temperature increases with advancing age, debilitating illness, or alcohol ingestion. Increased metabolic heat production may occur when the elderly person undergoes extreme exertion, has an infection with a febrile state, or has hyperthyroidism.

There are a number of drugs that can cause heat production or interfere with a person's ability to dissipate heat. These drugs include:

MMWR Heat Related Mortality --- Arizona 1993-2002, and United States, 1979-2002

Centers for Disease Control and Prevention - "Heat Stress in the Elderly"

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Beta-blocking drugs may increase the elderly person's risk of hyperthermia.