Heat stroke. (Editorials).

Our core body temperature is maintained within a very narrow range of normality, even in extreme environmental conditions, through an intricate system integrating various physical and biochemical processes coordinated by the hypothalamus. (1) Rarely when heat cannot be dissipated effectively, as may happen when the environmental temperature is elevated or as a result of strenuous physical exercise, heat syndromes develop. These have a wide spectrum, ranging from the relatively mild heat rash to heat edema, heat cramps, heat exhaustion, exertional heat injury, and the very serious, life-threatening, often fatal, heat stroke. (2,3)

Heat stroke is diagnosed by an elevated core body temperature (40[degrees] C or higher) accompanied by anhidrosis, hot dry skin, and central nervous system abnormalities such as attention deficit, impaired memory, drowsiness, delirium, convulsions, and coma. (4-6) It is sometimes fatal even if the body temperature is adequately reduced because the exaggerated acute-phase response, the altered expression of heat-shock protein released when cells are exposed to high temperatures, and immune system dysfunction often lead to inflammatory responses, intravascular coagulation, and multiorgan injury. (4,7,8)

Effective and timely treatment can reduce the mortality to less than 10%. (9) Those who survive, however; often have evidence of permanent neurologic impairment and long-term disabilities, especially if the condition is not aggressively and promptly treated. (10) Rhabdomyolysis and acute renal failure also may develop after the body temperature returns to normal levels. (11)

Clinicians therefore must have a high index of suspicion. (3,12,13) The subtle clinical signs may mislead inexperienced clinicians, cause them to consider other diagnoses, and delay the institution of appropriate therapeutic measures. This is associated with a worse prognosis. Public health care professionals have an important role to prevent and reduce the impact of heat syndromes. (14-16) An analysis of the heat-related deaths during two heat waves in Milwaukee, Wisconsin, in 1995 and 1999 revealed that in the second wave the heat-related deaths were 49% less than the figures anticipated based on the 1995 heat wave. Changes in public health awareness, readiness, and response, rather than differences in heat levels, were responsible for the better outcome. (17) Exertion-al heat syndromes are largely preventable. (18,21)

Persons particularly at risk of heat strokes include the elderly, the infants, the obese, patients with hyperthyroidism, those with chronic diseases, impaired mental functions, limited or no social contacts, and especially those with no access to air conditioning. (22,23) A multivariate analysis of the heat-related deaths during the 1999 heat wave in Chicago revealed that the strongest risk factors were living alone (odds ratio [OR] = 8.1; 95% confidence interval [CI] = 1.4-48.1) and not leaving home on a daily basis (OR = 5.8; 95% CI = 1.5-22.0). On the other hand, not unexpectedly, a working air conditioning system was the strongest protective factor (OR = 0.2; 95% CI = 0.1-0.7). (24) Similar findings were noted when the heat-related deaths during the 1993 heat wave in Philadelphia were examined. (25)

A number of medications and recreational drugs can also predispose to heat syndromes. (26,27) Older adults are particularly susceptible to heat syndromes because of dysfunctional thermoregulatory mechanisms, tendency to consume less fluids and therefore to become dehydrated, and because of the frequent presence of a number of pathologies that may interfere with the effective regulation of the body temperature, especially in times of stress as may happen when the environmental temperature increases suddenly.

As our summers may be getting warmer and more humid, we may expect more patients suffering from heat syndromes. Health care providers should be familiar with the presentation, diagnosis, and management of these conditions. More importantly still, the public needs to be aware of the potential dangers of heat syndromes and should be taught how to prevent them. Heat stroke is a medical emergency that could and should be prevented.

Ronald C. Hamdy, MD, FRCP, FACP 

Editor

References

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