Heatstroke: When Summertime Gets Too Hot

by Food and Drug Administration (FDA)

On the morning of July 7, 1996, a 74-year-old woman was found dead under her kitchen table in Fort Worth, Texas. A victim of heatstroke, she was using only a single fan to cool the house. She hadn't turned on her air conditioner to save money on the electric bill, her sister later told police.

The temperature inside the house was over 38 degrees Celsius (100 degrees Fahrenheit).

Last summer, seven people died of heatstroke in Texas. In the big heat wave of 1980, 78 people died.

"Heat has always been a health problem for Texas," says David Vaughan of the Texas Department of Health in Austin. "We get some real scorchers."

Texas and other southern states have the highest rates of heat illnesses and deaths, but such deaths can occur nearly anywhere. Typically, about 240 people in the United States die from heat illnesses each year, according to the national Centers for Disease Control and Prevention. During heat waves, that number has risen to as high as 1,700.

Heatstroke is one of several maladies known as heat illness. The others are heat syncope, heat cramps, and heat exhaustion. All of them occur when the body's ability to regulate its own heat is impaired, either because of exercise or exposure to hot temperatures. Certain health conditions and medications also increase the likelihood of heatstroke.

But, says Elizabeth Koller, M.D., an outdoor enthusiast and endocrinologist in FDA's Center for Drug Evaluation and Research, "Heatstroke is entirely preventable." Yet when it strikes, it becomes life-threatening.

"If someone is overheating, you have only minutes to do something about it," she says. "You have to cool them down as quickly as you can. Once their brain is overheated, that's it."

Body Heat Control

Our bodies are like car engines. They chug along, producing heat in the process. The skin and blood are like the cooling system of the car. Blood warms up as it passes through muscles and tissue. It carries extra heat to the surface of the skin, where the surrounding air cools it.

Unlike an engine, however, our bodies have the benefit of sweat, a very efficient cooling liquid. For example, a pearl-sized bead of sweat can cool nearly one liter (about 1 quart) of blood 1.8 C (1 F), using 580 calories in the process.

But in hot, humid weather, sweat doesn't work as well. The surrounding air is already warm and heavy with humidity, and it cannot absorb extra heat and sweat. So the body begins to warm up, and the heart begins pumping more blood to the skin to release the extra heat. Even if you sit still, your heart will beat faster. Have you ever felt tired after a day spent lounging on the beach? That fatigue comes from your heart working overtime to cool your body. If you sweat a great deal of water and lose enough minerals, you could develop one or more heat illnesses.

The mildest, most common heat syndrome is called heat cramps. It usually occurs in people who have been exercising in hot, humid weather. As the victim sweats, minerals are excreted from the body. This mineral depletion causes muscles to contract in slow, painful spasms lasting one to three minutes, usually after the person has stopped exercising. A person with heat cramps needs fluids, extra salts, a cooler environment, and rest.

A second syndrome is heat exhaustion (it has also been termed heat syncope or heat collapse). This syndrome occurs when a person has lost either too much water or too much salt through sweating. Depending on the cause, the victim may or may not have an elevated temperature. In either case, he or she will feel thirsty, nauseated, headachy, weak, and confused. The victim may soon pass out, pulse racing. A heat exhaustion victim needs to lie flat in a cool place, with water and electrolyte fluids to drink as soon as he or she regains consciousness. Intravenous fluids might be necessary.

Danger: Heatstroke

The most dangerous heat illness is heatstroke. Heatstroke is a life-threatening medical emergency. The victim may develop headache, slurred speech, dizziness, faintness, hallucinations, seizures, and may even become comatose. Body temperature soars to 40 C (104 F) or more. The person becomes so dehydrated that the skin no longer sweats and is hot and dry to the touch.

There are two types of heatstroke: classic and exertional. Classic heatstroke occurs in individuals who don't sweat normally, either because of a disease or certain medications. Without normal sweating, it's difficult for a person to handle hot, humid weather. The typical victim of classic heatstroke is an older adult who lives without air conditioning and has underlying health problems, such as heart disease or diabetes.

Classic heatstroke can take two or three days to develop, but it is very dangerous. Studies have shown that even a few hours of air conditioning each day can prevent the condition.

Exertional heatstroke, on the other hand, happens quickly — often after only a few hours of exercise. The skin is able to sweat, but the body still overheats because of the combination of hot weather, extra activity, and dehydration. Exertional heatstroke victims are usually young, otherwise healthy people, such as runners and football players.

Exertional heatstroke has long been studied by the military. The U.S. Marines at Parris Island, S.C., for example, have studied heat illness among new recruits. They found that even though soldiers train in the early morning and are required to drink lots of water, as many as 2 percent of them will suffer heat illnesses during the summer months, and about 1 percent in the winter. The risk of exertional heat injuries depends on the heat and humidity, the soldier's fitness level, and whether or not the person is used to hot weather.

The treatment for both classic and exertional heatstroke is the same: Cool the victim as quickly as possible with whatever means available — for example, wet sheets, a fan, or ice under the armpits. (While the military routinely uses ice to cool heatstroke victims, some studies have shown this can also cause frostbite.) Give the victim liquids, if possible, and get medical attention immediately. Early treatment increases a heatstroke victim's chance of survival.

About the Author

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.