Heat stroke (patient information)

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What are the symptoms?

What are the causes?

Who is at highest risk?


When to seek urgent medical care?

Treatment options

Where to find medical care for Hyperthermia?


What to expect (Outlook/Prognosis)?

Possible complications

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Directions to Hospitals Treating Hyperthermia

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Usama Talib, BSc, MD [2]


Heat stroke is defined as severe illness characterized by a core temperature >40°C and central nervous system abnormalities such as deliriumconvulsions, or coma resulting from exposure to environmental heat (classic heat stroke) or strenuous physical exercise (exertional heat stroke).

What are the symptoms of Hyperthermia?

Heat cramps are the first stage of heat illness. If these symptoms are not treated, it can lead to heat exhaustion and then heat stroke. Heat stroke occurs when the body is no longer able to regulate its temperature, and it keeps rising. Heat stroke can cause shock, brain damage, organ failure, and even death. The early symptoms of heat cramps include:

  • Muscle cramps and pains that most often occur in the legs or abdomen
  • Very heavy sweating
  • Fatigue
  • Thirst

Later symptoms of heat exhaustion include:

  • Headache
  • Dizziness, lightheadedness
  • Weakness
  • Nausea and vomiting
  • Cool, moist skin
  • Dark urine

The symptoms of heatstroke include (call 911 or the local emergency number right away):

  • Fever -- temperature above 104°F (40°C)
  • Irrational behavior
  • Extreme confusion
  • Dry, hot, and red skin
  • Rapid, shallow breathing
  • Rapid, weak pulse
  • Seizures
  • Unconsciousness

If not treated heat stroke symptoms can include:

  • organ failure
  • unconsciousness
  • death

What causes Heat Stroke?

Heat injuries can occur due to high temperatures and humidity. You are more likely to feel the effects of heat sooner if:

  • You are not used to high temperatures or high humidity.
  • You are a child or an older adult.
  • You are already ill from another cause or have been injured.
  • You are obese.
  • You are also exercising. Even a person who is in good shape can suffer heat illness if warning signs are ignored.
  • The following make it harder for the body to regulate its temperature, and make a heat emergency more likely:
  • Drinking alcohol before or during exposure to heat or high humidity
  • Not drinking enough fluids when you're active on warmer or hot days
  • Heart disease
  • Certain medicines: Examples are beta-blockers, water pills or diuretics, some medicines used to treat depression, psychosis, or ADHD
  • Sweat gland problems
  • Wearing too much clothing
  • Excessive exertion
  • Not taking enough fluids

Who is at highest risk?

People with following factors are at a greater risk of acquiring heat stroke:

Environmental factors

  • Heat waves
  • High humidity
  • Lack of air movement
  • Urban heat islands
  • Lack of air conditioning

Compromised health condition

  • Obesity
  • Acute illness
  • Skin disorders
  • Cardiovascular insufficiency

Genetic conditions


Classic heat stroke

Exertional heat stroke


What to do?

If you think a person may have heat illness or emergency:

  • Have the person lie down in a cool place. Raise the person's feet about 12 inches (30 centimeters).
  • Apply cool, wet cloths (or cool water directly) to the person's skin and use a fan to lower body temperature. Place cold compresses on the person's neck, groin, and armpits.
  • If alert, give the person a beverage to sip (such as a sports drink), or make a salted drink by adding a teaspoon (6 grams) of salt per quart (1 liter) of water. Give a half cup (120 milliliters) every 15 minutes. Cool water will do if salt beverages are not available.
  • For muscle cramps, give beverages as noted above and massage affected muscles gently, but firmly, until they relax.
  • If the person shows signs of shock (bluish lips and fingernails and decreased alertness), starts having seizures, or loses consciousness, call 911 and give first aid as needed.

When to seek urgent medical care?

Call 911 if:

  • The person loses consciousness at any time.
  • There is any other change in the person's alertness (for example, confusion or seizures).
  • The person has a fever over 102°F (38.9°C).
  • Other symptoms of heatstroke are present (like rapid pulse or rapid breathing).
  • The person's condition does not improve, or worsens despite treatment.

Treatment options

  • Remova from the environment
  • Cooling
  • Rehydration

Where to find medical care for Hyperthermia?

Directions to Hospitals Treating Hyperthermia


The first step in preventing heat illnesses is thinking ahead.

  • Find out what the temperature will be for the whole day when you will be outdoors.
  • Think about how you have dealt with heat in the past.
  • Make sure you will have plenty of fluids to drink.
  • Find out if there is shade available where you are going.
  • Learn the early signs of heat illness.

To help prevent heat illnesses:

  • Wear loose-fitting, lightweight and light-colored clothing in hot weather.
  • Rest often and seek shade when possible.
  • Avoid exercise or heavy physical activity outdoors during hot or humid weather.
  • Drink plenty of fluids every day. Drink more fluids before, during, and after physical activity.
  • Be very careful to avoid overheating if you are taking drugs that impair heat regulation, or if you are overweight or elderly.
  • Be careful of hot cars in the summer. Allow the car to cool off before getting in.

NEVER leave a child sitting in a car exposed to the hot sun, even after opening windows.

What to expect (Outlook/Prognosis)?

  • If addressed early the prognosis is good.

Possible complications

Life Threatening complications

Common Complications

Rare Complications

The rare complications include:


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