Heat collapse is characterised by fatigue, giddiness, and temporary loss of consciousness. It is accompanied by HYPOTENSION and BRADYCARDIA; there may also be vomiting and muscular cramps. Urinary volume is diminished. Recovery is usual.
Heat exhaustion is characterised by increasing weakness, dizziness and insomnia. In the majority of su?erers, sweating is defective; there are few, if any, signs of dehydration. Pulse rate is normal, and urinary output good. Body temperature is usually 37·8–38·3 °C.
Heat cramps (usually in the legs, arms or back, and occasionally involving the abdominal muscles) are associated with hard physical work at a high temperature. Sweating, pallor, headache, giddiness and intense anxiety are present. Body temperature is only mildly raised.
Heat hyperpyrexia is heralded by energy loss and irritability; this is followed by mental confusion and diminution of sweating. The individual rapidly becomes restless, then comatose; body temperature rises to 41–42 °C or even higher. The condition is fatal unless expertly treated as a matter of urgency.
Treatment With the ?rst two syndromes, the a?ected individual must be removed immediately to a cool place, and isotonic saline administered – intravenously in a severe case. The fourth syndrome is a medical emergency. The patient should be placed in the shade, stripped, and drenched with water; fanning should be instigated. He or she should be wrapped in a sheet soaked in cool water and fanning continued. When rectal temperature has fallen to 39 °C, the patient is wrapped in a dry blanket. Immediately after consciousness returns, normal saline should be given orally; this usually provokes sweating. The risk of circulatory collapse exists. Convalescence may be protracted and the patient should be repatriated to a cool climate. Prophylactically, personnel intended for work in a tropical climate must be very carefully selected. Adequate acclimatisation is also essential; severe physical exertion must be avoided for several weeks, and light clothes should be worn. The diet should be light but nourishing, and ?uid intake adequate. Those performing hard physical work at a very high ambient temperature should receive sodium chloride supplements. Attention to ventilation and air-conditioning is essential; fans are also of value.... Medical Dictionary