Section 24. Accidents and Injuries

Chapter 290. Heat Disorders

Topics: Introduction | Heat Cramps | Heat Exhaustion | Heatstroke

Introduction

Humans, who are warm-blooded animals, maintain their body temperature within a narrow range (within 1 or 2 degrees of 98.6° F) despite large fluctuations in external temperatures. This internal temperature range must be maintained for the body to function normally. Body temperature that gets too high or too low can result in serious injury to organs or death.

The body regulates its temperature by balancing heat production and heat loss. One way the body produces heat is through chemical reactions (metabolism) resulting mostly from the conversion of food into energy. Heat is also produced through the work of muscles during physical activity. The body cools itself by losing heat, mainly through the processes of radiation and sweating. Radiation, in which heat flows from warmer to cooler areas, is the main source of heat loss when the body is warmer than its environment. Sweating, in which the sweat glands produce moisture that cools the skin as it evaporates, is the main source of heat loss when the environment is warmer than the body and during exercise. However, humidity (the presence of moisture in the air) slows water evaporation, decreasing the effectiveness of sweating. Therefore, heat loss may be difficult in hot, humid weather.

Heat disorders are caused by too much heat production or by too little heat loss. Excessive sweating due to heat depletes the body of fluids and salts (electrolytes), which can lead to low blood pressure and painful muscle contractions. Which heat disorder develops depends on the severity of body fluid and salt depletion. Heat cramps result from mild or moderate depletion; heat exhaustion, from moderate or severe depletion; and heatstroke, the most serious of the heat disorders, often from severe depletion.

Ineffective heat loss most commonly occurs in hot, humid conditions. Several factors contribute greatly to ineffective heat loss. Wearing heavy, tight, waterproof clothing that does not breathe (that is, that does not allow air and moisture to pass through easily) prevents sweat from evaporating from the skin surface, thus impairing cooling. Sweating can be impaired by certain drugs, most often antipsychotic drugs and drugs with anticholinergic effects (see Section 2, Chapter 14); by some diseases that affect the skin, such as cystic fibrosis, scleroderma, psoriasis, and eczema; and by severe sunburns. Obesity impairs sweating as well because it requires the heart to work harder, thereby depleting the reserve needed to increase pumping for sweating. Also, a thick layer of fat slows heat loss from internal organs, which may sustain damage from prolonged heat exposure. Alcohol interferes with sensible responses that could prevent heat disorders. For example, an inebriated person may not move to a cool environment, remove heavy clothing, or turn on an air conditioner.

Excessive heat production is most often caused by fever, increased thyroid activity, extreme exertion, and certain stimulant drugs, such as cocaine and amphetamines. Strenuous muscular activity occurs by choice or results from medical conditions such as seizures, agitation, or alcohol or drug withdrawal.

The chance of developing heat disorders increases when exposure to heat occurs suddenly, such as when a child is left in a closed car on a hot summer day. When a person is exposed to longer periods of heat and humidity, the body gradually adjusts and is better able to maintain normal body temperature. This process is called acclimatization. Acclimatization occurs no more rapidly in young or physically active people than in older or physically inactive people.

Prevention

Using common sense is the best way to prevent heat disorders. For example, strenuous exertion in a very hot environment should be avoided. During hot, humid weather, it is best to wear light, loose-fitting clothing made of cloth that breathes (that is, that allows air and moisture to pass through easily), such as cotton. Fluids and salts lost through sweating can be replaced by consuming lightly salted foods and beverages, such as salted tomato juice or cool bouillon. Many commercially available drinks contain extra salt. To replace adequate amounts of fluids, drinking must continue even after thirst is quenched. When exertion in a hot environment cannot be avoided, drinking plenty of fluids and frequently cooling the skin by misting or wetting it with cool water can help keep body temperature near normal.

People engaged in outdoor activities who drink large quantities of water may dilute the sodium in the blood. Consuming salt, even in salty "junk" food, along with the water can alleviate this problem.

Enclosed, poorly ventilated spaces, such as a car, can heat up rapidly. In hot weather, the interior of a closed car can heat from 80 to 120° F in 15 minutes. Children and pets should never be left in such an environment, even for a few minutes.