Hyperthermia

Hyperthermia is an increase in body temperature above 99° F, but most often the term is used to refer to a dangerously high body temperature.

Fever is a more general term that describes any increase above 99° F. It is usually reserved for situations in which body temperature is elevated for reasons other than a warm environment, such as a response to infection.

When an older person's surroundings are hotter than his body temperature, heat cramps, heat exhaustion, or heatstroke can occur. Heat cramps and heat exhaustion usually involve an increase in body temperature, although some people with these disorders have a normal body temperature. Heatstroke always involves a dangerously high body temperature.

High body temperature is never the sole cause of the symptoms of heat cramps, heat exhaustion, and heatstroke. Symptoms also stem from the loss of body fluids and dissolved salts (electrolytes), especially sodium and potassium, in the blood.

Causes

An older person's body temperature may rise whenever the body produces too much heat or when it is unable to get rid of excess heat. The body gains excess heat when the air is warmer than 98.6° F. When high humidity accompanies high air temperature, the body has difficulty getting rid of excess heat, because humid air makes evaporation of sweating less effective. Heat is also produced during physical activity by muscles. Thus, most cases of hyperthermia occur on hot days, especially humid ones, and in people who are exerting themselves.

The chance of developing hyperthermia increases when a person is exposed to high heat suddenly. Such a situation might occur when an older person stays inside during a heat wave with windows closed and with no air-conditioning because of poverty or loss of electrical power. As a person is exposed to longer periods of high heat and humidity, the body gradually adjusts (acclimates) and is better able to maintain usual body temperature. Older people, however, are not as able as younger people to acclimate to higher temperatures and humidity. In addition, they more commonly have underlying diseases or take drugs that interfere with their ability to eliminate heat.

For additional detail on this topic, see The Body's Response to Warm Temperatures.

Symptoms and Diagnosis

Hyperthermia produces symptoms proportional to its severity.

Heat cramps, the mildest form, can develop with modest losses of fluids and electrolytes. Heat cramps are felt as waves of painful contractions in muscles of the hands, shoulders, feet, calves, or thighs. The muscles become hard and tense.

Heat exhaustion often results in dizziness that is typically described as light-headedness. Fainting may occur, especially upon standing after a period of sitting or lying down. Drenching sweats are common. Mild confusion, headache, blurred vision, weakness, fatigue, muscle aches, nausea, or vomiting may develop.

Heatstroke, the most severe form, sometimes develops without any warning symptoms. The first sign of trouble may be severe confusion, bizarre behavior, or a coma. In some cases, however, light-headedness, mild confusion, headache, blurred vision, weakness, fatigue, muscle aches, nausea, or vomiting may develop early on. Seizures may occur. Some people with heatstroke, especially people who have been physically exerting themselves, are still sweating. More commonly, however, the skin becomes hot, flushed, and dry. Sweating often stops despite the heat, and the person urinates very little or not at all.

A doctor makes the diagnosis of heat exhaustion and heatstroke on the basis of symptoms. A physical examination often shows the heart rate and breathing rate to be increased. Blood pressure may be low in heat exhaustion and is often extremely low in heatstroke. In heat exhaustion, body temperature can be normal or high, but not higher than 104° F. In heatstroke, body temperature usually exceeds 105° F and may be so high that it can no longer be read on a typical thermometer. Blood tests are done to determine if the levels of sodium and potassium are low.

Prevention

Common sense is the best tool for preventing hyperthermia. During hot, humid weather, older people are advised to take the following precautions:

• Avoid strenuous exertion. When exertion in a hot environment cannot be avoided, drinking plenty of liquids and frequently cooling the skin by misting or wetting it with cool water can help keep body temperature near normal.
• Wear light, loose-fitting clothing made of cloth that allows air and moisture to pass through easily, such as cotton.
• Replace fluids and salts lost through sweating by consuming lightly salted foods and beverages, such as salted tomato juice or cool bouillon. Many commercially available drinks contain extra salt. To adequately replace fluids, drinking must continue even after thirst is quenched.
• Use air-conditioning or fans. It is especially important that the bedroom be air-conditioned. People who live in homes without air-conditioning or fans should open windows at night and create cross-ventilation by opening windows on two sides of the building. Windows should be covered with curtains, shades, or blinds during daylight hours to reduce the heat from the sun. When transportation is available, older people who live in homes that are not air-conditioned can go to public places that are air-conditioned, such as shopping malls, movie theaters, or libraries.

Outlook and Treatment

Mild heat cramps can often be treated by moving to a cooler environment and drinking beverages that contain salt. Severe heat cramps are treated with fluids and salts given intravenously. Drugs to treat fever, such as acetaminophen and aspirin, are ineffective and should not be used.

If body temperature continues to rise, untreated heat cramps or heat exhaustion can progress to heatstroke. Fortunately, most older people with heat cramps or heat exhaustion recover fully when appropriately treated.

Many older people do not survive heatstroke. Because of the danger and the need for specialized treatment and monitoring, people with heatstroke are usually best treated in an emergency department and then admitted to an intensive care unit of a hospital.

An older person with heatstroke must be cooled immediately. After calling for medical assistance, the caller should remove the person's clothing, splash water on his skin, and then fan him. Ice packs should not be used to cool the person, because shivering produces heat. At the hospital, body cooling is usually accomplished by spraying the body with tepid water. To speed evaporation and body cooling, a fan is used to blow air on the body. Ice packs are also placed over large blood vessels in the neck, genital region, and armpits. Body temperature is measured continuously. Cooled fluids may be given intravenously. To avoid overcooling, efforts to cool the body are halted when the temperature is reduced to about 102° F.

After recovery, body temperature may remain abnormal and fluctuate for weeks. The brain may not fully recover, and an older person who has had heatstroke may be left with personality changes, clumsiness, or poor coordination.