New Perspectives on Heat Stroke
ABSTRACT & COMMENTARY
Source: Dematte JE, et al. Near-fatal heat stroke during the 1995 heat wave in Chicago. Ann Intern Med 1998;129:173-181.
In july 1995, an eight-day heat wave struck chicago, ultimately resulting in 3300 excess emergency department (ED) visits and 600 excess deaths. Dematte and associates, representing a number of Chicago-area hospitals and the CDC, report on the clinical features of non-exertional heat-stroke patients surviving ED resuscitation to be admitted to the ICU and the status of victims one year after discharge. Enrollment criteria for the study included 1) ICU admission during the heat wave, 2) abnormal mental status, 3) anhydrosis, 4) absence of vigorous physical activity, and 5) core temperature greater than 105°F or documentation that the patient was cooled prior to determination of temperature.
Fifty-eight heat-stroke victims were included in this study, with a mean age of 68 years and a slight male majority. Forty percent had a history of hypertension, and 29% were alcoholic. Most patients were taking one or more medications, although only one quarter were taking a drug known to be associated with heat stroke. Two patients had positive tests for cocaine. The mean hospital stay was nine days, and 60% required mechanical ventilation.
More than half of patients had a documented infection at the time of admission, which were most commonly bacteremia and urinary tract infections. The majority of patients developed moderate-to-severe renal insufficiency. Disseminated intravascular coagulation (DIC) was seen in 66% of patients who had DIC profiles performed. Cardiovascular, pulmonary, and hepatic abnormalities were frequent but nonspecific. Twelve patients (21%) did not survive hospitalization, and an additional 28% had died by one year. Of those discharged, 76% had significant neurologic impairment. There was no improvement in functional performance at one-year follow-up. Neurologic impairment proved to be the strongest predictor of mortality.
COMMENT BY DAVID J. KARRAS, MD, FACEP
Heat-related illnesses are reported as the primary cause of death between 150 and 1700 times a year in the United States.1 Far more individuals succumb to other underlying illnesses that are exacerbated by extreme heat. Our understanding of heat stroke is derived from a large number of case reports and small case series and is plagued by the flaws inherent in deriving a knowledge base from anecdotal information. This study is the largest and most comprehensive study of a single heat-stroke epidemic. A few findings are surprising, particularly the high prevalence of infection at the time of presentation. The correlation between functional status and mortality is not unexpected, although it is intriguing that neurological impairment was the only independent predictor of death. The 36% overall, one-year mortality rate is sobering.
This study has important limitations. No attempt was made to determine premorbid neurological function; functional status at discharge, therefore, provides limited information. Because neurologic deficit is a common predisposing factor to heat stroke, it is likely that some patients had an abnormal mental status at baseline. It is unclear how many patients actually had profound hyperthermia. Although temperature is notoriously unreliable in diagnosing heat stroke, it is possible that some patients had fever and mental status changes related to their infection and were not actually heat-stroke victims. Indeed, several patients in this study were found in air conditioned environments.
Notably, Dematte et al state that a cooling time of longer than 30 minutes is unacceptable, although only one victim was cooled this rapidly and most were cooled in 1-2 hours. Furthermore, Dematte et al advocate ice- or cold-water immersion without mentioned evaporative cooling techniques. Most practitioners of emergency medicine find that management of an immersed patient is practically impossible, and cooling within 30 minutes is a desirable but frequently elusive goal.
References
1. Heat-related illnesses and deaths-United States 1994-1995. MMWR Morb Mortal Wkly Rep 1995;44: 465-468.
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