The human body usually can regulate its temperature. When the body gets too hot, it uses several strategies to cool down, including sweating. But if a person spends too much time in the heat without taking in enough fluids, the body's cooling processes can't work properly. When the body becomes dehydrated, it can no longer cool itself by sweating. When this happens, body temperature can rise high enough to make the person sick.
The first symptoms of heat illness occur as the body temperature climbs above normal, and can include headache, nausea, vomiting, muscle cramps and fatigue. These early symptoms sometimes are called heat exhaustion. If steps are not taken to reduce body temperature, heat exhaustion can worsen and become heat stroke.
Heat stroke is a serious, potentially life-threatening form of heat illness. The body temperature rises to 105 degrees Fahrenheit or higher and you develop neurological changes, such as mental confusion or unconsciousness. At these high temperatures, body proteins and the membranes around the cells in the body, especially in the brain, begin to be destroyed or malfunction. The extreme heat can affect internal organs, causing breakdown of the heart muscle cells and blood vessels, damage to internal organs, and death. There are two main causes of heat stroke:
- Exertional heat stroke occurs when someone is vigorously active in a hot environment, such as playing sports on a hot summer day or participating in military training activities. It typically strikes young, otherwise healthy people, those least likely to be concerned about the effects of heat on their health. Because of the lack of concern, early symptoms may be dismissed or ignored.
- Nonexertional heat stroke tends to occur in people who have a diminished ability to regulate body temperature, such as older people, very young children or people with chronic illnesses. High heat in the surrounding environment, without vigorous activity, can be enough to cause heat stroke in these people.
Factors that can contribute to heat stroke include:
- Dehydration from not drinking enough water
- Wearing bulky or heavy clothing, such as firefighting gear, in the heat
- Being overweight, which causes the body to generate more heat and reduces the body's ability to cool down
- Sleep deprivation, which can decrease the rate of sweating
- Being unaccustomed to the heat, such as moving from a cooler climate to a warmer climate
- Some medications, most commonly antihistamines (taken for allergies), diuretics (taken for high blood pressure or leg swelling), laxatives (taken to relieve constipation), calcium channel blockers (one type of blood pressure or heart medicine), medicines for Parkinson's disease, some diarrhea treatments and tricyclic antidepressants
- Being confined to a poorly ventilated or non-air-conditioned living space
- Having had heat stroke in the past
- Use of illicit drugs, including cocaine, heroin, amphetamines and ecstasy (MDMA)
Heat stroke can come on suddenly, but warning symptoms often appear first. They include:
- Abdominal cramps
- Muscle cramps
- Heavy sweat or a lack of sweat
When heat stroke starts, neurological symptoms can include:
- Odd or bizarre behavior
A doctor will examine the person and do tests to check for other possible causes of the high temperature. Tests may include a computed tomography (CT) scan of the head, blood tests and a lumbar puncture (spinal tap).
The doctor also will do urine and blood tests to monitor how well the kidneys are functioning. Dehydration and heat stroke can be a major stress for the kidneys.
It is standard for a person with heat stroke to stay in the hospital for one or more days so that any complications can be identified quickly. Complete recovery from heat stroke and its affects on body organs may take two months to a year.
Most cases of heat stroke can be prevented. When the temperature outside is especially high:
- Drink lots of water throughout the day.
- Stay indoors in an air-conditioned area whenever you feel too warm.
- Wear lightweight, light-colored clothing, preferably with a loose-weave material that lets air get to your skin.
- Avoid strenuous activity in the hottest part of the day (between 10 a.m. and 4 p.m.). If you must participate, take frequent breaks, limit the time that you wear a helmet by taking it off between activities, and avoid wearing heavy uniforms or equipment.
- Drink less caffeine and alcohol, which can contribute to dehydration.
If you begin to feel tired, dizzy or nauseated, or if you develop a headache, get out of the heat immediately. Seek out an air-conditioned building. Drink water. If possible, take a cool shower or bath or use a hose to soak yourself.
The first step in treating heat stroke is to reduce body temperature by cooling the body from the outside. This can be done by removing tight or unnecessary clothing, spraying the person with water, blowing cool air on the person, or wrapping the person loosely in wet sheets. Alternatively, ice packs can be placed at the neck, groin and armpits to accelerate cooling.
If these methods do not lower body temperature enough, a doctor may try to lower temperature from the inside by flushing the stomach or rectum with cold water. Severe cases may require cardiopulmonary bypass, in which the person's blood is diverted from the heart and lungs into a collection machine, cooled, and then returned to the body.
In some cases, anti-seizure or muscle-relaxing medications may be given to control convulsions and shivering. Aspirin and acetaminophen (Tylenol) do not help lower body temperature when a person has heat stroke, and these medications should be avoided if heat stroke is suspected.
People with heat stroke generally need to be hospitalized so they can be tested for complications that may appear after the first day. One common complication is muscle breakdown caused by the heat. In this condition, called rhabdomyolysis, byproducts of the muscle breakdown appear in the bloodstream and can damage the kidneys.
Seek emergency help if you or someone else has been in the heat and experiences confusion, faintness, staggering, hallucinations (visions that are not real), unusual agitation or coma. Begin cooling the person immediately.
If medical help is sought quickly, heat stroke almost always is treated successfully. Having had heat stroke in the past increases your risk of heat stroke in the future, so you will have to take extra precautions in hot weather. Delaying treatment can have serious consequences, including kidney or liver damage, congestive heart failure or heart arrhythmias, coma or death.
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