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On a hot July day at noon, you answer the call for help from bystanders watching a parade. A victim in his 60s is lying face-up on some grass. Your victim assessment finds that the victim is unresponsive but breathing. His skin is hot and dry. You have other bystanders help move him into the shade. He is admitted later to the hospital intensive cardiac care unit and eventually recovers and is released. Sound familiar? It does happen.

From 1979 to 1992, there were about 5,379 deaths in the United States associated with excessive heat. Several recent heat waves have resulted in high death rates in some urban areas. From July 1 through July 4, 1993, the Eastern United States experienced high temperatures with high humidity. Last July, 529 deaths in Chicago were attributed to heat during a heat wave so dramatic that it overtaxed emergency medical service capabilities and city morgue facilities.

Heat loss

Heat loss occurs in several ways. Radiation is a form of heat loss in which the body emits heat into the environment without requiring the movement of air, provided that the air temperature is lower than the body temperature. Conduction involves the transfer of thermal energy via the body's contact with such things as a chair, water or even the surrounding air. Convection is the exchange of air molecules between the body and the environment. Warm air is less dense than cooler air, and as warm air molecules rise away from the body surface they are replaced by cooler air molecules. The processes of conduction and convection can be enhanced by the presence of a breeze or the wind. A combination of convection and radiation accounts for about 70 percent of our heat exchange process.

When the environmental temperature is greater than our body temperature we gain heat through radiation and conduction, so the body initiates perspiration and sweating to lose heat. The body is cooled as water evaporates off the skin. When the environmental temperature gets above 95 degrees, most body heat is lost through this process. However, when the humidity exceeds 75 percent, sweating and evaporation are no longer as efficient.

As water evaporates from the body surface it carries body heat with it. Sweating, therefore, is categorized as being very important.

Heat risk groups

The elderly, those with underlying medical problems, those unable to get out of hot environments, those who use certain medications, those who consume alcohol and those who are not normally active in hot environments are all prone to heat-related emergencies.

Types of heat emergencies

Heat syncope is the onset of sudden unresponsiveness that is usually corrected once the victim is placed flat on the ground or floor.

Heat cramps are slow, painful muscle cramps and spasms that occur in the most commonly used muscles, such as those in the legs and abdomen. Cramps occur when fluids are lost by sweating and replaced only with water.

Heat exhaustion, one of the most common heat-related problems, results from dehydration and sodium loss due to sweating. Individuals prone to this condition include those who were dehydrated prior to the heat exposure, the elderly and those with hypertension.

Heatstroke is the least common yet most deadly form of a heat-related emergency, with an approximate 70 percent mortality rate. Most cases involve the elderly and the disabled. In heatstroke, the body's hypothalmic temperature regulation abilities are lost, resulting in an uncompensated rise in body temperature. Heatstroke is considered present when the skin is hot and the victim has an altered mental status.

There are two classifications of heatstroke: classic and exertional. Classic heatstroke tends to occur during heat waves and affects primarily the very young, the elderly and the disabled. Exertional heatstroke tends to involve younger individuals who are physically fit and athletic. Classic heatstroke victims have hot, dry skin while 50 percent of the exertional heatstroke victims will have wet skin that is also very hot.

First aid

Remove the victim from the heat and into a shaded area or air-conditioned room. Remove as much clothing as possible to facilitate cooling. Replace lost electrolytes and restrict physical activity.

In high humidity, place ice packs on the victim's armpits and groin. If in low humidity, cover the victim with a sheet and spray with water. Fanning also helps. Avoid inducing shivering, alcohol baths or submersing the victim in water. Stop cooling when a heatstroke victim's mental status is normal.

If the victim is responsive, drinking water with added salt or sport drinks containing electrolytes are recommended. Avoid the use of alcoholic drinks and salt tablets.