Heat Exhaustion

Medical Editor:

Heat Exhaustion Facts

  • Heat exhaustion is a condition that occurs when the body overheats.
  • Heat exhaustion is caused by the failure of the body's cooling mechanism to maintain a normal core temperature.
  • Symptoms of heat exhaustion may include
  • Heat exhaustion is diagnosed based on the patient's history of heat exposure, physical exam, symptoms and a body core temperature that is elevated.
  • Treatment for heat exhaustion includes removing the individual from the hot environment, cooling the body, and rehydration.
  • Complications of heat exhaustion include progression to heat stroke, a medical emergency that can lead to permanent organ damage and death. In pregnant women, it may harm the fetus.
  • Heat exhaustion can be prevented by adequate fluid intake and decreasing strenuous activity in hot environments. Pregnant women develop more heat intolerance as their pregnancy advances.
  • Animals (dogs and cats, for example) can develop heat exhaustion, and the treatment and prevention is similar to that of humans.

What Causes Heat Exhaustion?

The main cause of heat exhaustion is failure of the body's cooling mechanism (mainly evaporative sweating) to maintain a normal core body temperature, resulting in the body overheating. This can occur in adults, children and animals (dogs and cats, for example). Factors that can contribute to heat exhaustion include

  • strenuous work or exercise in a warm or hot environment,
  • dehydration,
  • alcohol intake, and
  • wearing clothing that inhibits evaporative cooling of the body.

The elderly and children under 5 years of age are at higher risk for developing heat exhaustion.

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What Are the Symptoms and Signs of Heat Exhaustion?

People with heat exhaustion may have some or all of these symptoms;

  • Weakness
  • Muscle cramps
  • Heavy sweating
  • Headache
  • Nausea and vomiting
  • Weak and rapid pulse
  • Thirst
  • Clammy skin
  • Dizziness and/or fainting

Individuals with heat exhaustion will generally have an elevated body core temperature (internal temperature, not skin temperature).

When Should I Call the Doctor About Heat Exhaustion?

An individual should be evaluated by a doctor or other health care professional if they develop symptoms consistent with heat exhaustion. This can result in the early diagnosis and treatment of heat exhaustion, which can prevent the individual from becoming worse and potentially developing heat stroke (body core temperature of 104 F/40 C or higher) and other complications.

How Is Heat Exhaustion Diagnosed?

The diagnosis of heat exhaustion is generally made after obtaining the patient's history and performing a physical exam. If the body core temperature is elevated (but less than 104 F/40 C in adults or less than 105 F/40.5 C in children), and the patient has had heat exposure along with the symptoms of heat exhaustion, then the diagnosis of heat exhaustion can be made. However, in some instances, blood and urine testing may be done to check for other causes or to detect certain abnormalities that may be associated with the early signs of heat stroke, such as electrolyte abnormalities, rhabdomyolysis (muscle breakdown) and/or kidney damage. Other tests may also be ordered to exclude other diagnostic possibilities, depending on your doctor's evaluation.

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Causes of Dehydration: Sweat

The body can lose significant amounts of water when it tries to cool itself by sweating. Whether the body is hot because of the environment (for example, working in a warm environment), intense exercising in a hot environment, or because a fever is present due to an infection; the body uses a significant amount of water in the form of sweat to cool itself. Depending upon weather conditions, a brisk walk will generate up to 16 ounces of sweat (one pound of water).

What Is the Treatment for Heat Exhaustion?

Treatment for heat exhaustion should begin immediately when a person is suspected of having heat exhaustion, and the primary treatment is evaporative cooling and removing the person from the hot environment.

  • The person should be placed in the shade or in a cool building while awaiting transport to a medical facility.
  • Have the individual lie down, with their legs elevated above the level of the heart.
  • Remove any restrictive clothing the person is wearing if it inhibits evaporative cooling.
  • Cooling can be aided by misting the skin with cool water and then circulating air with fans in order to increase evaporative cooling (a cool water shower may also help, if available).
  • Provide the person with refrigerated drinks such as Gatorade or other sports drinks.
  • Additionally, intravenous fluids may be given by medical personnel to treat dehydration.

Heat Exhaustion in Children

Heat exhaustion in children occurs for the same reasons (causes) listed previously for adults, but children are more susceptible to dehydration. Symptoms of heat exhaustion may include:

  • fatigue,
  • nausea,
  • vomiting,
  • dehydration,
  • headache,
  • clammy skin,
  • rapid breathing, and
  • irritability.

Treatment of heat exhaustion in children is similar to that of adults.

  • Put the child in the shade or and air conditioned building
  • Loosen or remove tight or excessive clothing
  • Cool the child with evaporative cooling (mist skin with cool water and use fans) or give the child a cool (not cold) bath
  • Encourage Pedialyte or a sports drink
  • Seek medical care

If the child's body temperature reaches 105 F/40.5 C or above, or any other symptoms of heat stroke develop (such as the absence of sweating, seizures, lethargy or loss of consciousness), call 911 immediately. As in adults, untreated heat exhaustion in children may quickly progress to heat stroke and potentially death.

Heat Exhaustion in Dogs and Other Animals

Animals with fur coats can overheat quickly in hot environments. Symptoms may vary according to the type of animal, so it is recommended that you consult with your animal's veterinarian about heat exhaustion.

Though this article is not designed to cover animal heat exhaustion in depth, the signs and symptoms of heat exhaustion in dogs, for example, may include weakness and excessive panting. As with humans, the dog's core temperature may be elevated.

Animals that show signs of heat exhaustion should be treated in the same way as humans (see above). For dogs (and cats), massage of the legs will help circulation and increase body cooling.

First Aid Pictures Slideshow: 8 First Aid Essentials for Car or Purse

How Can I Prevent Heat Exhaustion?

Prevention of heat exhaustion is accomplished by taking reasonable precautions. The precautions are as follows:

  • Avoid hot environments when possible (do not sit in a closed vehicle in the summer or do heavy physical work in hot areas without planned cool-down periods).
  • Avoid sunburns.
  • Wear light colored clothing and light-weight clothing that does not fight tightly.
  • Drink a lot of fluids (if your urine frequency slows or your urine seems more concentrated, you need to drink more fluids), and avoid alcoholic beverages.
  • Give your body time (at least a few days) to adjust to a hot climate before doing strenuous activities.
  • Check with your pharmacist or doctor to see if your medications may make you more susceptible to heat-related problems (for example, diuretics, sedatives, and stimulants).
  • Infants, children, the elderly, and pregnant women are all more susceptible to heat exhaustion than other individuals because their bodies do not cool as efficiently. Infants, children and some elderly are dependent on others to manage their environment and to take precautionary measures to avoid heat exhaustion.
  • Pregnant women develop more heat intolerance as the pregnancy progresses.
  • Dogs and other animals may also be dependent on others to provide adequate precautions (shade, fluids) in order to avoid heat exhaustion.

What Is the Prognosis for Heat Exhaustion?

If people are treated early and effectively, then the prognosis for heat exhaustion is almost always very good. However, if heat exhaustion is not detected and treated, then heat stroke may develop resulting in possible organ damage, seizures, coma and even death.

Reviewed on 11/21/2017

Medically reviewed by Avrom Simon, MD; Board Certified Preventative Medicine with Subspecialty in Occupational Medicine

REFERENCES:

Kidshealth.org. Heat Stroke and Heat Exhaustion Instruction Sheet.

Kidshealth.org. Heat Illness.

R. S. Helman, MD. et al. Heatstroke Differential Diagnoses. Medscape. May 2015
<http://emedicine.medscape.com/article/166320-differential>

University of Maryland Medical Center. Heat exhaustion.

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