Heat exhaustion and heatstroke

ANATOMY OR SYSTEM AFFECTED: Blood vessels, circulatory system, skin

DEFINITION: Heat-related illnesses in which the body temperature rises to dangerous levels and cannot be controlled through normal mechanisms, such as sweating.

Causes and Symptoms

The human body is well equipped to maintain a nearly constant internal body temperature. In fact, the body temperature of human beings is usually controlled so closely that it rarely leaves a very narrow range of 36.1 to 37.8 degrees Celsius (97 to 100 degrees Fahrenheit) regardless of how much heat the body is producing or what the environmental temperature may be. Humans maintain a constant temperature so that the millions of biochemical reactions in the body remain at an optimal rate. An increase in body temperature of only one degree Celsius will cause these reactions to move about 10 percent faster. As internal temperatures rise, however, brain function becomes slower because important proteins and enzymes lose their ability to operate effectively. Most adults will go into convulsions when their temperature reaches 41 degrees Celsius (106 degrees Fahrenheit), and 43 degrees Celsius (110 degrees Fahrenheit) is usually fatal.

A special region of the brain known as the hypothalamus regulates body temperature. The hypothalamus detects the temperature of the blood, much like a thermostat detects room temperature. When the body (and hence the blood) becomes too warm, the hypothalamus activates heat-loss mechanisms. Most excess heat is lost through the skin by the radiation of heat and the evaporation of sweat. To promote this heat loss, blood vessels in the skin dilate (open up) to carry more blood to the skin. Heat from the warm blood is then lost to the cooler air. If the increase in blood flow to the skin is not enough, then sweat glands are stimulated to produce and secrete large amounts of sweat. The process, called perspiration, is an efficient means of ridding the body of excess heat as long as the humidity is not too high. In fact, at 60 percent humidity, evaporation of sweat from the skin stops. When the body cannot dissipate enough heat, heat exhaustion and heatstroke may occur.

Heat exhaustion is the most prevalent heat-related illness. It commonly occurs in individuals who have exercised or worked in high temperatures for long periods of time. These people have usually not ingested adequate amounts of fluid. Over time, the patient loses fluid through sweating and respiration, which decreases the amount of fluid in the blood and leads to dehydration. Because the body is trying to reduce its temperature, blood has been shunted to the skin and away from vital internal organs. This reaction, in combination with a reduced blood volume, causes the patient to go into mild shock. Common signs and symptoms of heat exhaustion include cool, moist skin that may appear either red or pale; headache; nausea; dizziness; and exhaustion. If heat exhaustion is not recognized and treated, it can lead to life-threatening heatstroke.

Heatstroke occurs when the body is unable to eradicate the excess heat as rapidly as it develops. Thus, body temperature begins to rise. Sweating stops because the water content of the blood decreases. The loss of evaporative cooling causes the body temperature to continue rising rapidly, soon reaching a level that can cause organ damage. In particular, the brain, heart, and kidneys may begin to fail until the patient experiences convulsions, coma, and even death. Therefore, heatstroke is a serious medical emergency that must be recognized and treated immediately. The signs and symptoms of heatstroke include high body temperature (41 degrees Celsius or 106 degrees Fahrenheit); loss of consciousness; hot, dry skin; rapid pulse; and quick, shallow breathing.

Treatment and Therapy

As with most illnesses, prevention is the best medicine for heat exhaustion and heatstroke. When exercising in hot weather, people should wear loose-fitting, lightweight clothing and drink plenty of fluids. When individuals are not prepared to avoid heat-related illness, however, rapid treatment may save their lives. When emergency medical personnel detect signs and symptoms of sudden heat-induced illness, they attempt to do three major things: cool the body, replace body fluids, and minimize shock.

For heat exhaustion, the initial treatment should be to place the patient in a cool place, such as a bathtub filled with cool (not cold) water. The conscious patient is given water or fruit drinks, sometimes containing salt, to replace body fluids. Occasionally, intravenous fluids must be given to return blood volume to normal in a more direct way. Hospitalization of the patient may be necessary to be sure that the body is able to regulate body heat appropriately. Almost all patients treated quickly and effectively will not advance to heatstroke. The activity that placed the patient in danger should be discontinued until one is sure all symptoms have disappeared, and steps have been taken to prevent a future episode of heat exhaustion.

Heatstroke requires urgent medical attention, or the high body temperature will cause irreparable damage and even death. Body temperature must be reduced rapidly. With the patient in a cool environment, the clothing is removed, and the skin sprinkled with water and cooled by fanning. Contrary to popular belief, rubbing alcohol should not be used, as it can cause closure of the skin’s pores. Ice packs are often placed behind the neck and under the armpits and groin. At these sites, large blood vessels come close to the skin and are capable of carrying cooled blood to the internal organs. Body fluid must be replaced quickly by intravenous administration because the patient is usually unable to drink as a result of convulsions or confusion and may even be unconscious. Once the body temperature has been brought back to normal, the patient is usually hospitalized and watched for complications. With early diagnosis and treatment, 95 to 97 percent of previously healthy people will survive.

In 2023 and 2024, first responders in the Southwest began using plastic immersion bags, whether specially designed bags or body bags, filled with water and ice to create a "body cocoon" to rapidly cool heat-stricken patients. The US military developed the cold water immersion technique in the 1990s. Since then, researchers have found that cold water immersion can reduce body temperatures eight times faster than other cooling techniques and that the risk of triggering a stroke, heart attack or other issues were minimal, especially if responders used a rectal thermometer to closely monitor the patient's body temperature.

Bibliography

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