Injury: Heat Stroke

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Injury: Heat Stroke

Causes and Symptoms
The Future
For more information


Heat stroke is the most severe of the three forms of heat-related illness. In heat stroke, a person's body temperature rises to 104°F (40°C) or higher. Unlike heat cramps and heat exhaustion, however, heat stroke

is a life-threatening condition. It has two forms: exertional heat stroke (EHS), related to work or exercise in the heat; and nonexertional heat stroke (NEHS), which is not caused by working or exercising outside and primarily affects the elderly, chronically ill persons, and infants during heat waves.


Heat stroke is a medical emergency that develops when a person's body can no longer get rid of excess heat through sweating and evaporation of the sweat. As a result, the body's core temperature rises, damaging the proteins and cell membranes in the body tissues and leading to organ failure, destruction of muscle tissue, the collapse of the cardiovascular system, and eventually death.


According to the CDC, over 8,000 people died in the United States from heat-related illness between 1979 and 2003. People over the age of sixty-five account for 44 percent of heat-related deaths.

Heat stroke affects people from all races and ethnic groups. Men and women are equally affected by heat stroke; however, men are twice as likely as women to die from heat stroke because more men than women

are employed in occupations that require working outdoors in hot weather.

Some groups of people have a greater risk of heat stroke:

  • Newborn infants. The body of a baby cannot adjust to changes in temperature as efficiently as an adult's. In addition, babies have a limited ability to exit a hot environment.
  • Elderly people. As with infants, the bodies of elderly people do not regulate internal temperature as effectively as those of younger adults. In addition, elderly people may have underlying illnesses or take medications that make them more vulnerable to heat stress.
  • Workers whose jobs require working outdoors in hot weather or near ovens, blast furnaces, or other sources of heat.
  • People who are not physically fit or have not undergone a conditioning program to get their bodies used to work or exercise in the heat.
  • People who take certain types of medications, including diuretics, drugs that regulate blood pressure, tranquilizers, antihistamines, and drugs given to treat people with schizophrenia.
  • Homeless people.
  • Obese people.

First Aid for Heat Stroke

The Centers for Disease Control and Prevention (CDC) give the following instructions for treating someone with heat stroke:

  • Have someone call 911 while the person is being cooled as rapidly as possible.
  • Depending on what is available nearby, the affected person can be cooled by putting him or her in a tub with cool water; spraying the person with a garden hose; putting the person in the shower and running cool water over them; or sponging the person with a damp cloth dipped in cool water.
  • Take the person's temperature from time to time if a thermometer is available, and keep cooling them until it drops to 101–102°F (38.3–38.8°C).
  • Call a hospital for further instructions if rescue workers are delayed.
  • Do not give the person water to drink.
  • If possible, loosen or remove some of the person's clothing.

Causes and Symptoms

Like heat exhaustion, heat stroke is caused by the loss of water and salt from the body due to sweating during exposure to heat or vigorous physical exercise in hot conditions. High humidity makes it harder for the body to regulate its internal temperature through sweating, which is its normal way to get rid of heat when the outside temperature is 95°F (35°C) or higher. As sweat evaporates, it carries body heat with it.

In addition to losing water through sweating, however, the body also loses electrolytes, which are minerals that are necessary to proper body functioning. In heat stroke, the body's cooling mechanisms are overwhelmed, and the body's internal temperature starts to rise uncontrollably.

Other factors that can impair the body's ability to regulate its temperature in hot, humid weather include drinking alcohol, which leads to losing more water through the urine, and wearing tight clothes or clothes made of fabrics that do not allow sweat to evaporate easily.

Heat stroke is often preceded by the symptoms of heat exhaustion, which include nausea and vomiting, headache, muscle cramps, dizziness, and difficulty breathing. The symptoms of heat stroke itself usually include:

  • Hot, flushed, dry skin
  • Changes in level of consciousness, including hallucinations, confusion, and irrational behavior
  • Rapid heartbeat, sometimes as high as 130 beats per minute
  • Rapid, shallow breathing
  • Blood pressure may be either normal or low
  • Body temperature above 104°F (40°C) or rectal temperature above 106°F (41.1°C).


The diagnosis of heat stroke is usually obvious from the patient's situation and previous activities. In addition to taking the patient's temperature, doctors in the emergency room may also take a urine sample to check kidney function or a blood sample to check the level of the patient's electrolytes and blood sugar. A blood test can also be used to evaluate whether the patient's liver has been damaged. In addition to these laboratory tests, the doctor may also order a muscle function test to see whether the patient's muscle tissue has begun to break down.


Immediate treatment for heat stroke is essential as death or permanent brain damage can occur within minutes. Emergency treatment is focused on cooling the patient as quickly as possible to a core body temperature of 102°F (38.9°C). Cooling may be done by spraying water on the body, covering the patient with sheets soaked in ice water, or placing ice packs

in the patient's armpits and groin area. The patient's temperature is not lowered further because they may start to shiver, and shivering will raise their internal temperature again.

If the patient is conscious, they may be given additional oxygen to breathe and intravenous fluids to restore their blood volume. In most cases these fluids will contain sugar in order to lower the risk of liver failure. Patients who are having muscle cramps or convulsions are usually given benzodiazepine tranquilizers, which relax the muscles and reduce the risk of damage to muscle tissue.

The patient will be kept in the hospital for at least forty-eight hours after emergency treatment and monitored for brain damage, signs of liver failure, or other complications. This period of observation is necessary because heat stroke can damage almost all major body systems.


Although people have survived body temperatures as high as 114.8°F (46°C), any temperature above 106°F (41.1°C) is potentially fatal. People who receive prompt treatment for heat stroke have a 90 percent chance of survival; without prompt treatment, 80 percent will die.


Heat stroke is largely preventable by taking time to adjust to hot weather and dressing sensibly for local weather conditions:

  • Most people in temperate climates need time to acclimate to seasonal temperature changes. People should work up gradually to sports and other outdoor activities during the first few warm days of summer rather than overdoing. The same is true of visiting a country with a tropical or hot climate; it is best to keep one's activity level moderate for a few days rather than crowding in too many activities. It can take people between seven and fourteen days to adjust to a hot climate; marathon runners generally take two weeks to acclimate to training in the heat.
  • Wear loose-fitting and light-colored clothing; choose fabrics that absorb sweat, such as cotton; wear a hat outdoors.
  • Drink fluids before exercising or working outside in hot weather. The American College of Sports Medicine recommends drinking about 20 ounces (0.6 liter) of water or sports drink two to three hours prior to exercise, and 10 ounces (0.3 liter) of water or a sports drink ten to twenty minutes before exercise. Do not use thirst as a guide to fluid intake; a person can become dehydrated before feeling thirsty enough to want a drink.
  • Use sunscreen generously, as sunburn lowers the body's ability to get rid of excess heat.
  • Avoid caffeinated beverages and alcohol; they cause the body to lose additional fluid through the urine.
  • People who must take prescription medications for allergies, high blood pressure, heart conditions, or certain types of mental disorders should ask their doctor whether any of their medications affect their response to hot weather.
  • Exercise during the early morning or late evening, when the temperature is cooler and the humidity lower. Workers in occupations that require them to work in hot environments should take rest breaks during periods of hot weather. Some companies also provide rest areas where workers can cool off.
  • Consult a heat stress index like the one printed in the American Council on Exercise fact sheet listed below or the National Weather Service's heat index to help decide whether it is safe to exercise outdoors. There are times when the heat and humidity are so high that exercise should be avoided. Heat stroke is likely to occur when the heat stress index (the apparent temperature) is over 105°F (40.5°C) and the person is exposed to it for a long period of time; if the heat index is 130°F (54.4°C) or higher, heat stroke is highly likely even with short exposure.
  • People with elderly friends or relatives should check on them during summer heat waves. Heat waves that last longer than two days put the elderly at risk of heat exhaustion.
  • People who do not have air conditioning in their homes should go to a library, shopping mall, or other public building that is air-conditioned during a heat wave. Even a few hours in a cooler location can help to lower the risk of heat stroke.

The Future

Heat stroke is a common hot-weather disorder; it is often a consequence of exercising or working outdoors without proper conditioning or precautions. Heat stroke can be prevented in normally healthy individuals by

dressing appropriately for hot weather, drinking enough fluids, consulting the local heat index before outdoor activity, and knowing when to slow down and cool off.

It is possible that heat stroke may become more common in some parts of the United States in the summer time because of the growing size of the elderly population and others who do not tolerate heat well because of chronic illness. One problem is geography: most parts of the United States have uncomfortably high temperatures for at least part of the summer, and some areas have temperatures at or above 90°F (32.2°C) for weeks on end. In addition, large cities tend to be hotter than the surrounding areas.

SEE ALSO Heat cramps; Heat exhaustion


Acclimation: The process of adjusting to seasonal climate changes or to a new climate.

Conditioning: The process of becoming physically fit through a program of diet, exercise, and rest.

Electrolytes: Minerals that are essential for proper body functioning. They include potassium, sodium, calcium, and magnesium.

Heat illness: A general term for heat-related disorders, ranging from heat cramps (the mildest) to heat stroke (the most serious).

For more information


Armstrong, Lawrence E., ed. Exertional Heat Illnesses. Champaign, IL: Human Kinetics, 2003.

Dvorchak, George. The Pocket First-Aid Field Guide: Treatment and Prevention of Outdoor Emergencies. Accokeek, MD: Stoeger Publishing Company, 2007.

Isaac, Jeff. Outward Bound Wilderness First-Aid Handbook, revised and updated. Guilford, CT: Falcon Guides, 2008.


Comeau, Matthew. “A Hot Issue for Summer Exercisers.” American College of Sports Medicine Fitness Page, Summer 2001, p. 4. Available online in PDF format at (accessed June 9, 2008).


Centers for Disease Control and Prevetion (CDC). Extreme Heat: A Prevention Guide to Promote Your Personal Health and Safety. Available online at (updated August 15, 2006; accessed June 9, 2008).

Mayo Clinic. Heatstroke. Available online at (updated September 7, 2007; accessed June 9, 2008).

National Institute for Occupational Safety and Health (NIOSH). Working in Hot Environments. Available online at (updated 1992; accessed May 7, 2008).

National Oceanic and Atmospheric Administration (NOAA), National Weather Service. Heat Safety Heat Index. Available online at (accessed December 9, 2008).

National Weather Service and the American Red Cross. Heat Wave: A Major Summer Killer. Available online at (updated June 8, 2007; accessed June 9, 2008). This is a guide to prevention of and basic first aid for heat-related illness.

Nemours Foundation. Heat Illness. (updated March 2007; accessed May 2, 2008).