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Heatstroke !hEt-+strOk

by James P. Knochel, MD

Heatstroke is a life-threatening condition that results in very high body temperature and malfunction of many organ systems.

  • Heatstroke can develop after hours of exertion in young athletes or after days of hot weather in rooms without air-conditioning in very old people.

  • Body temperature is higher than 104° F (40° C), and the brain malfunctions.

  • People should be cooled immediately.

Heatstroke is the most severe form of heat-induced illness. People with heatstroke are much sicker than people with other heat disorders. The following features in particular distinguish heatstroke from other heat disorders:

  • Body temperature is usually higher than 104° F.

  • Symptoms of brain malfunction develop.

Heatstroke may occur when people exert themselves in extreme heat or is in a closed, hot environment. For example, heatstroke can develop in young, healthy athletes, particularly those who are not acclimatized, after only hours of intense exertion in hot, humid weather. Heatstroke can also develop over days of hot weather when people, particularly older sedentary people, stay in rooms that are poorly ventilated and not air-conditioned. Older people, people who have certain medical conditions (such as those that involve malfunction of the heart, lungs, kidneys, or liver), and young children are most vulnerable to heatstroke.

Heatstroke occurs because the body cannot lose heat rapidly enough in conditions of extreme heat. Because the body cannot cool itself, body temperature continues to rise rapidly to dangerously high levels. Conditions that interfere with heat loss, including certain skin disorders, and drugs that decrease sweating increase the risk.

Heatstroke can temporarily or permanently damage vital organs, such as the heart, lungs, kidneys, liver, and brain. The higher the temperature, especially when higher than 106° F (41° C), the more rapidly problems develop. Death may occur.


Dizziness, light-headedness, weakness, fatigue, headache, blurred vision, muscle aches, nausea, and vomiting (which are also symptoms of heat exhaustion) are common warning symptoms. Affected people do not sense that body temperature is greatly elevated.

During heatstroke, the skin becomes hot, flushed, and dry. Sweating may not occur despite the heat. Because of brain malfunction, people may become confused and disoriented and may have seizures or go into a coma. The heart rate and breathing rate increase. The pulse rate is usually rapid. The blood pressure may be high or low. Body temperature usually exceeds 104° F and may be so high that it exceeds the markings on a typical thermometer.


The diagnosis is usually evident. People have a high fever, symptoms of brain malfunction, and a history of being exposed to high heat and humidity. If the diagnosis is not evident, tests are done for other disorders that can cause similar symptoms, such as infections, stroke, and an overactive thyroid gland (hyperthyroidism).


The body must be cooled immediately, and an ambulance should be called. While awaiting transportation to the hospital, people should be wrapped in cold, wet bedding or clothing; immersed in a lake, stream, or cool bathtub; or cooled by being immersed in ice-cold water. Misting the body with water and then blowing air across the body with a fan is also very effective. Using drugs (aspirin or acetaminophen) designed to treat a fever due to an infection is useless and should be avoided.

Did You Know...

  • Drinking large amounts of plain water during exertion can dangerously dilute sodium in the bloodstream.

At the hospital, the body is usually cooled rapidly by removing the clothes and covering the exposed skin with water or occasionally ice. To speed evaporation and body cooling, a fan may be used to blow air on the body. Body temperature is measured frequently, often constantly. Cooled fluids may be given intravenously. To avoid overcooling, cooling is stopped when the body temperature is reduced to about 102° F (about 39° C).

Seizures, coma, and malfunction of other organs may also need treatment. Heatstroke is best treated in an intensive care unit of a hospital.


The risk of death from heatstroke climbs depends on the following factors:

  • How old adults are

  • How young children are

  • How severe any conditions (such as heart, lungs, kidneys, or liver disorders) are

  • What the highest body temperature is

  • How long body temperature remains extremely high

In about 20% of people who survive, the brain may not fully recover, leaving a person with personality changes, clumsiness, or poor coordination. In some people, the kidneys do not fully recover. After recovery, body temperature may fluctuate abnormally for weeks.

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