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        The four disorders that com prise the spectrum of illness due to heat exposure are heat syncope, heat cramps, heat exhaustion and heat stroke. At normal temperatures, evaporation accounts for approximately 20 per cent of the body's heat loss, but at high temperature it becomes the major mechanism for dissipation of heat; with vigorous exertion, sweat loss can be as much as 2.5 litres/hour. This mechanism diminishes as humidity rises.

        Medical evaluation and monitoring should be used to identify individuals at increased risk of heat disorders. The public should be made aware of the early symptoms and signs of heat disorders. It is not recommended to make salt tablets available for use without medical supervision; close monitoring of fluid and electrolyte intake may be necessary in situations necessitating activity in hot environments.

        Acclimatisation is achieved by scheduled regulated exposure to hot environments and by gradually increasing the duration of exposure and the work load until the body adjusts by producing sweat of lower salt content in greater amounts at lower ambient temperatures.

        Specific syndromes due to heat exposure, as explained by Dr S Sathyanarayanan of Sri Chakra Hospital, Nanganallur are:

        1 Heat syncope: Sudden unconsciousness is the result due to heat. Systolic blood pressure is usually less than 100 mm Hg. And there is typically a history of vigorous physical activity for two hours or more just preceding the episode. The skin is typically cool and moist, and the pulse is weak. Treatment consists of rest and recumbency in a cool place, with fluids by mouth (or intravenously, if necessary).

        2 Heat cramps: Fluid and electrolyte depletion can result in slow, painful skeletal muscle contractions (cramps) and severe muscle spasms lasting 1-3 minutes, usually of the muscles most heavily used. Cramping results from salt depletion as sweat losses are replaced with water alone. Laboratory evaluation may show low serum sodium, hemo-concentration, and elevated urea and creatinine.

        The patient should be moved to a cool environment and given oral saline solution (4 tsp of salt per gallon of water) to replace both salt and water. The victim may have to rest for 1-3 days with continued dietary salt supplementation before returning to work or resuming strenuous activity in heat.

        3 Heat exhaustion: Heat exhaustion results from prolonged strenuous activity with inadequate water or salt intake in a hot environment and is characterised by dehydration, sodium depletion, or isotonic fluid loss with accompanying cardio-vascular changes.

        Treatment consists of patient location in a shaded, cool environment, providing adequate hydration (1-2 litres over 2-4 hours), salt replenishment - orally if possible - and active cooing (fans, ice packs, etc) if necessary. Intravenous 3 per cent (hypertonic) saline may be necessary if sodium depletion is severe. At least 24 hours rest is recommended.

        4 Heat stroke:

        Heat stroke is life-threatening medical emergency resulting from failure of the thermo-regulatory mechanism. Heat stroke is imminent when the core (rectal) temperature approaches 41 deg C. It presents in one of the two forms: Classic heat stroke occurs in patients with compromised homeostatic mechanisms and Exertional heat stroke occurs in healthy persons undergoing strenuous exertion in a thermally stressful environment. Morbidity or even death can result from cerebral, cardio-vascular, hepatic or renal damage, caused by heat stroke. The hallmarks of heat stroke are cerebral dysfunction with impaired consciousness, high fever and absence of sweating. Heat stroke may resent with dizziness, weakness, emotional lability, nausea and vomiting, diarrhoea, confusion, delirium, blurred vision, convulsions, collapse and unconsciousness.

        Treatment is aimed at reducing the core temperature rapidly (within one hour) while supporting organ system function. Evaporating cooling is rapid and effective and is easily performed in most emergency settings. The patient's clothing should be removed and the entire body sprayed with water (20 deg C) while ambient or slightly warmed air is passed across the patient's body with large fans or other means at high velocity.