Heat illness. A report of 45 cases from Hong Kong

Health Risks and Interventions in Exertional Heat Stress

BACKGROUND

With climate change, heat waves are expected to become more frequent in the near future. Already, on average more than 25 000 "heat deaths" are estimated to occur in Europe every year. However, heat stress and heat illnesses arise not just when ambient temperatures are high. Physical exertion increases heat production within the organism many times over; if not enough heat is lost, there is a risk of exertional heat stress. This review article discusses contributing factors, at-risk groups, and the diagnosis and treatment of heat illnesses.

METHODS

A selective literature search was carried out on PubMed. Current guidelines and expert recommendations were also included.

RESULTS

Apart from muscular heat production (>70% of converted energy), there are other factors that singly or in combination can give rise to heat stress: clothing, climate/acclimatization, and individual factors. Through its insulating properties, clothing reduces the evaporation of sweat (the most effective physiological cooling mechanism). A sudden heat wave, or changing the climate zone (as with air travel), increases the risk of a heat-related health event. Overweight, low fitness level, acute infections, illness, dehydration, and other factors also reduce heat tolerance. In addition to children, older people are particularly at risk because of their reduced physiological adaptability, (multi-)morbidity, and intake of prescription drugs. A heat illness can progress suddenly to life-threatening heat stroke. Successful treatment depends on rapid diagnosis and cooling the body down as quickly as possible. The aim is to reduce core body temperature to <40 °C within 30 minutes.

CONCLUSION

Immediately effective cooling interventions are the only causal treatment for heat stroke. Time once lost cannot be made up. Prevention (acclimatization, reduced exposure, etc.) and terminating the heat stress in good time (e.g., stopping work) are better than any cure.

Severe heatstroke complicated with Takotsubo cardiomyopathy

Case

A 69 year-old female with history of schizophrenia was transported to our hospital by ambulance due to coma. On arrival, she was hypotensive and tachycardic with a Glasgow coma scale score of 3 and a rectal core temperature of 40°C. Heatstroke was strongly suspected as the cause of the coma and hypotension. Active external cooling with an electric fan and cooled IV fluid administration were started. Her electrocardiogram (EKG) showed ST elevation in V2-6, II, III and aVF. Echocardiography revealed apical ballooning, which indicated Takotsubo cardiomyopathy. Coronary angiography indicated normal coronary arteries.

Outcome

After admission to the intensive care unit, her cardiovascular status gradually improved and she was transferred to the psychiatric ward on day 36.

Conclusion

Heatstroke and Takotsubo cardiomyopathy can share the same pathophysiology. Close evaluation of hemodynamic status and myocardial damage is critical for survival.

Exertional heat stroke

The increasing popularity of mass participation endurance events necessitates that on-site medical teams be well versed in the management of both common and life-threatening conditions. Exertional heat stroke is one such condition, which if left untreated can be fatal.

Heat-stroke: a review of rapid cooling techniques

Patients with prolonged hyperpyrexia due to heat-stroke have a poor outcome. Thus, the most important feature in the management of heat-stroke is rapid cooling. There are several methods of cooling available, such as fan therapy, cold water immersion, iced baths and evaporative cooling. Based on military and civilian experiences worldwide the development of protocols based on evaporative cooling is advocated as the most efficient.

Heat illness in Cyprus

Heat illness in the Armed Forces is an emotive issue. No specific service-wide system currently exists to monitor the incidence of heat illness. Within British Forces Cyprus medical policy guidelines for physical activity at various Wet Bulb Globe Temperature (WBGT) readings were issued in 1988. A local system for reporting heat casualties was introduced in August 1989. This paper examined retrospectively the reports of heat illness casualties from August 1988 to December 1992 in Cyprus. There was a reduction in reported incidents causing heat casualties over the period studied from 18 incidents in 1990 to 8 in 1992. There was also a reduction in the maximum recorded WBGT reading for each incident. From these results it would seem that there may have been a reduction in preventable heat casualties attributable to commanders following the WBGT guidelines.

Animal models for heat stroke studies

Heat stroke is a medical emergency where quick diagnosis and management of victims are essential for positive prognosis. Several biochemical, physiological and hematological changes were observed in heat stroke. It seems that all of these changes are a consequence of induced tissue damage, or may have been a compensatory action by the body. Induction of hyperthermia and temperature measurement are important components in heat stroke studies to determine the stage of progression or regression of heat stroke. Several animal models have been established by investigators in heat related studies. Rats, dogs, monkeys, baboons, cows, rabbits, sheep and chicks have all been used in such studies that allow manipulation of exposure conditions and various designs of experiments. Amongst these species, rats, rabbits and sheep are the most suitable models because of their similarity to man in response to high temperature and in relation to their availability, cost and simplicity of handling. Such models may be used to study various pharmacological and biochemical parameters and functions concurrently. Further informations could also be obtained from isolated organ studies. The present review is to analyse and compare the available methodology for heat stroke studies.

Heat-exercise hyperpyrexia

A fatal case of "heat stroke" occurring on exercise in temperate conditions is described. Possible mechanisms for increased susceptibility are discussed and attention is drawn to a possible overlap with the malignant hyperpyrexia (MH) syndrome. The second day of strenuous exercise may be a time of special risk. More frequent consideration of dantrolene treatment in heat injury is suggested and the term "heat-exercise hyperpyrexia" is proposed to replace "heat stroke" and "exertional hyperpyrexia".