HEATSTROKE

debility caused by exposure to high temperature and humidity. The term sunstroke refers to the same disorder when exposure to direct sunlight is the main source of environmental heat. The fundamental feature of heatstroke is an extreme and uncontrolled elevation of body temperature (106 to 110 F [41 to 43 C], or even higher), which can harm the central nervous system. There is good evidence that heatstroke in its uncomplicated form is caused by the failure of sweating to cool the body. The average human body produces 70 calories of heat per hour at rest and up to eight times this figure in severe muscular work. In mild climates this heat is eliminated by radiation and convection from the skin and lungs and by evaporation of sweat. As the surroundings become hotter, all methods of heat elimination become ineffective except the evaporation of sweat. Experiments involving prolonged work in heat demonstrate a slow decline in the rate of sweating. Thus, physiologic mechanisms for control of body temperature seem to become fatigued if exposure to heat is prolonged. When the sweat rate is insufficient, rapid changes may occur, including a further drop in or near cessation of sweating, a rapid rise in temperature, collapse, and coma. If prompt treatment by cooling is not instituted, the victim will die. It is notable that continuous exposure to heat for many hours is usually necessary to produce heatstroke. In the early stages of heatstroke the victim may experience dizziness, headache, nausea, weakness, restlessness, or mental confusion and has a rapid bounding pulse and hot, dry, flushed skin. As collapse persists, the coma deepens and a weak, thready pulse and a more dusky skin will follow. Cooling of the body is urgent if the victim's life is to be saved. Ice-water baths or packs, with massage to promote circulation, are effective. Cooling should be stopped when the rectal temperature reaches 102 F (39 C) but should be reinstituted if temperature rises again. After this first-aid procedure, expert medical care is necessary to manage the effects of possible circulatory disorder and brain damage. Death from such residual damage is not unusual. The recovered patient may have increased susceptibility to the ill effects of heat. Persons exposed to extreme environmental heat often experience other difficulties. They need large amounts of water and salt to replace those lost in the sweat. Without sufficient water, they suffer from dehydration and may collapse from inadequate circulation. This collapse, whether caused by dehydration or other phenomena, is called heat exhaustion, or heat prostration. It can be distinguished readily from heatstroke by the moderate or absent elevation of body temperature and by the persistence of heavy sweating. Salt, or other mineral, and sugar depletion may contribute to heat exhaustion or cause other difficulties, among them heat cramps, which are relieved specifically by supplying added salt, minerals, or sugar to the diet. Although such difficulties may complicate or even precipitate heatstroke, they are complications rather than essential features. Heat exhaustion is treated by lying down in a cool place and drinking water to which salt has been added, though any fluid (such as fruit juice) is helpful.