HEAT DISORDERS

DEFINITION

Heat disorders are a group of illnesses caused by prolonged exposure to hot temperatures, restricted fluid intake, or failure of the body's ability to regulate its temperature. The general term used for heat disorders is hyperthermia (pronounced hi-per-THUR-mee-uh). The three most common forms of hyperthermia are heat exhaustion, heat stroke, and heat cramps.

DESCRIPTION

Hyperthermia can cause harm to people of all ages. But its effects are more serious with increasing age. The conditions that cause heat cramps in a teenager may cause a more serious form of hyperthermia—heat exhaustion—in a middle-aged person. Those same conditions may cause even more serious effects in an older person, a form of hyperthermia known as heat stroke.

The human body functions normally only within a very narrow range of temperatures close to 98.6°F (37°C). If the body gets much warmer or much colder than 98.6°F, health problems develop. Raising or lowering the body temperature by only a few degrees can cause death in a short period of time.

The body's temperature control center is in the brain. It senses changes in internal and external temperatures. It determines the changes that must be made to keep body temperature at 98.6°F. It then relays instructions to the body's cells to make these changes.

One method the body uses to cool down is perspiring (sweating). Perspiration is the loss of water from the skin. Body heat provides the energy needed to evaporate water from the skin. The more a person perspires, the cooler the body becomes.

However, excessive perspiration can cause problems. The body may lose too much water. It may become dehydrated. Dehydration can cause a variety of medical problems.

Heat Cramps

Heat cramps are the least serious form of hyperthermia. They are the first sign that the body is having difficulty with increased temperature. Heat cramps are a warning sign that more serious problems may soon develop.

Heat Exhaustion

Heat exhaustion is more serious than heat cramps. The condition may be caused when a person is exposed to high temperatures for a long period of time. Or the body may become dehydrated, or its temperature regulation system may begin to fail. Heat exhaustion is a common problem among athletes, firefighters, construction and factory workers, and anyone who wears heavy clothing in hot weather.

Heat Stroke

Heat stroke is the most serious form of hyperthermia. The condition can cause death in a short period of time. Heat stoke often results in death. The conditions that lead to heat stroke are the same as those that cause heat exhaustion. However, those conditions cause more serious symptoms in the case of heat stroke.

CAUSES

The primary cause of all types of hyperthermia are prolonged exposure to hot temperatures, restricted fluid intake, or failure of the body's ability to regulate its temperature. The three forms of hyperthermia are caused by progressively greater exposure to heat.

SYMPTOMS

Symptoms for the different types of hyperthermia vary. The longer one is exposed to heat, the more serious the symptoms of hyperthermia become.

Heat Cramps

At relatively warm temperatures, the body begins to perspire. Perspiration results in the loss of water. The body slowly becomes dehydrated. Dehydration leads to heat cramps.

As heat cramps develop, muscle tissue becomes less flexible. It becomes more difficult and more painful to move. Muscles in the legs are most frequently affected. A person may find it difficult to walk or maintain his or her balance. Young children, the elderly, and people with circulation problems are more likely to be affected by heat cramps.

Heat Exhaustion

After hours in a hot environment, perspiration increases and body temperature rises. The skin may appear cool, moist, and pale. Other symptoms of heat exhaustion include headache, nausea, exhaustion, and a general sense of weakness. Before long, dizziness, faintness, and mental confusion develop.

Heat exhaustion is a common problem among athletes, firefighters, construction and factory workers, and anyone who wears heavy clothing in hot weather. (©

Richard Hutchings

. Reproduced by permission of

Photo Researchers, Inc.

)

Breathing becomes rapid and shallow. The urine of a person with heat exhaustion is likely to be dark yellow or orange.

Heat Stroke

Under the most extreme conditions, the body's temperature regulation system may begin to fail. The brain is no longer able to send messages to the rest of the body telling it how to cool off. Heat stroke may occur after the body temperature has reached 104°F (40°C). At this point, the patient may become mentally confused and aggressive. He or she may begin to stagger and feel faint.

During heat stroke, a patient's pulse rate may reach 160 to 180 beats per minute. The skin appears to be dry and flushed. There is very little perspiration. At this point, the patient needs immediate medical attention. Without care, he or she may die in a matter of hours.

DIAGNOSIS

Most cases of hyperthermia can be diagnosed easily. The two key factors are the patient's visible symptoms and recent personal history. A tennis player who collapses while playing a game, for example, may be suspected of having hyperthermia. Testing that person's temperature, heart rate, and other vital factors may confirm the diagnosis quickly.

Blood and urine tests can also be used to confirm a diagnosis of hyperthermia. In any form of hyperthermia, the balance of chemicals in blood and urine changes. Laboratory tests can detect these changes and confirm the presence of hyperthermia.

TREATMENT

The first steps in treating any form of hyperthermia include:

• Moving the patient to a cooler location.
• Providing the patient with cool water.
• Giving the patient liquids that contain electrolytes.

Electrolytes are chemicals that occur naturally in the body and that maintain the proper balance of fluids in the body. The usual liquids given a patient are salt water that contains a low concentration of salt, or a sports drink such as Gatorade.

The patient should not be given salt tablets. The concentration of salt in tablets is too high for the body to absorb. Salt tablets can make a case of hyperthermia more serious, rather than improving it.

The above steps are often sufficient to treat most cases of heat cramps and heat exhaustion. Massage of leg muscles can also offer relief from the pain and soreness of heat cramps. Patients with heat exhaustion should be made to lie down with their feet elevated.

Cases of heat stroke require emergency treatment by trained medical personnel. While waiting for this help, some first aid measures can be taken. Ice packs should be placed around the neck, under the arms and knees, and in the groin. Medical treatment may involve intravenous feeding of fluids and electrolytes. Bed rest is often necessary for many days.

PROGNOSIS

Prompt treatment of heat cramps and heat exhaustion is usually successful. Patients recover in a matter of hours or, at most, a day or two. Heat stroke poses more serious problems. Prognosis depends on the patient's age and general health. In the most serious cases, heat stroke can lead to permanent damage to internal organs, and even death.

PREVENTION

The general rules for avoiding any form of hyperthermia are the same. One should avoid strenuous exercise when it is very hot. Wearing light, loose-fitting clothing can also help. An important factor in preventing hyperthermia is consumption of sufficient amounts of liquids. The warmer it becomes and the more active a person is, the greater the body's need for liquids. Caffeine and alcohol should be avoided in hot conditions because they can contribute to dehydration, increasing the risk of hyperthermia. Eating lightlysalted foods can also help replace electrolytes lost during perspiration.

FOR MORE INFORMATION

Books

American Red Cross. Standard First Aid. St. Louis, MO: Mosby Year Book, 1993.

Larson, David E., ed. Mayo Clinic Family Health Book, 2nd edition. New York: William Morrow, 1996.

Morris, M., M. Walsh, and Shelton G. Walsh. The Team Physicians Hand Book. Philadelphia: Hanley & Belfus, 1990.