Heat Stroke – Heat Hyperpyrexia

Heat stroke follows exposure to heat and is characterized by hyperpyrexia owing to deranged heat regulatory mechanism. Neuropsychiatric disturbance are prominent. Heat stroke occurs at temperatures ranging from 4 to 45 degrees or above, but may also occur at wet bulb temperatures as low as 30- 35 degrees Celsius, especially if the humidity is high. Precipitating factors include unaccustomed and sustained heavy work at high temperatures, alcoholism, infections, dehydration, use of drugs like atropine, obesity, and lack of acclimatization. The abnormality in heat regulation is due to a suddent failure of the sweating mechanisms. Persons with congenital or acquired diseases of the sweat glands suffer more.

Clinical features: The onset is sudden or even abrupt with a rapid rise of body temperature to 41 degrees Celsius or more with acute neurological features such as confusion, restlessness, delirium, agitation, convulsions and coma. In a few patients there may be prodromata, including headaches, giddiness, thirst and restlessness and the onset is gradual.

The cardinal diagnosis features are hyperpyrexia, neuro-psychiatric disturbances, and a hot and dry skin (hot dry man). The temperature (oral or rectal) varies from 41.5 to 44 degrees Celsius. It is preferable to take the rectal tachycardia and tachypnea. Electro-cardiogram show T wave changes suggestive of myocardial involvement. Complications include jaundice, bleeding tendencies and acute renal failure. Untreated, the condition is fatal owing to circulatory hepatic or renal failure.

Diagnosis: diagnosis should be suspected in the presence of the three cardinal features, viz hyperpyrexia, neurologic disturbances, and a hot and dry skin in a subject exposed to high ambient temperature. It is important to rule out falciparum malaria. Malaria may co-exist with heat stroke but in cerebral malaria the peripheral blood will show signs of malarial hyperinfection. Other conditions like septicemia, typhus, pyogenic meningitis, encephalitis, pontine hemorrhage, and closed head injuries have to be excluded.

Laboratory features of heat stroke include neutrophile leucocytosis, thrombocytopenia, elevation of blood urea and bilirubin, and reduction of plasma bicarbonate.

Treatment: Heat stroke is a medical emergency . Treatment aims at the reduction of the rectal temperature to 39 degrees Celsius within one hour and restoration of the circulating blood volume. The patient is covered with wet sheets or towels and sprayed with cold water while air is blown or fanned over him to promote evaporative cooling. As an alternative, the patient may be immersed in cold water. The limbs are gently massaged to promote circulation. When the rectal temperature falls to 38 degrees, the patient is transferred to a cool room and watched for further rise of temperature. Recurrence is quite common and temperature regulation may remain unstable for weeks.

Prompt and effective cooling restores neurological functions in the majority of patients. Chlorpromazine (25-50 mg) administered intravenously is a useful adjunct during cooling. If there is suspicion of malaria, antimalarials are given parenterally. Shock and cardiac failure have to be treated appropriately. Sequelae include headache, insomnia, giddiness, cerebellar dysfunction and even coma. Most of these clear up in the course of weeks or months.

Prognosis: If left untreated, 50-70% of subjects die of stroke. Early treatment reduces the mortality to 15-20%. Shock also carried a bad prognosis. Prognosis worsens in patients who have high temperature and in whom treatment is delayed.