Heat disorders

Definition

Heat disorders are a group of physically related illnesses caused by prolonged exposure to hot temperatures, restricted fluid intake, or failure of temperature regulating mechanisms of the body. Disorders of heat exposure include heat cramps, heat exhaustion, and heat stroke (also called sunstroke).

Description

Hyperthermia is the general name given to heat-related illnesses. The two most common forms of hyperthermia are heat exhaustion and heat stroke, the latter of which is especially dangerous and requires immediate medical attention.

The thermal regulation centers of the brain help to maintain the body's internal temperature. Regardless of extreme weather conditions, the healthy human body keeps a steady temperature of approximately 98.6°F (37°C). In hot weather or during vigorous activity, the body perspires. As perspiration evaporates from the skin, the body is cooled. The thermal regulating centers in the brain help the body adapt to high temperatures by adjusting the amount of salts (electrolytes) in the perspiration. Electrolytes help the cells in body tissues maintain water balance. In hot weather, a healthy body will lose enough water to cool the body while creating the lowest level of electrolyte imbalance. If the body loses too much salt and fluid, symptoms of dehydration will occur.

Heat cramps

Heat cramps are the least severe of the heat-related illnesses. This heat disorder is often the first signal that the body is having difficulty with increased temperature. Individuals exposed to excessive heat should view heat cramps as a warning sign of a potential heat-related emergency.

Heat exhaustion

Heat exhaustion is a more serious and complex condition than heat cramps. Heat exhaustion can result from prolonged exposure to hot temperatures, restricted fluid intake, or failure of temperature regulation mechanisms of the body. Heat exhaustion requires immediate attention, as it can rapidly progress to heat stroke.

Heat stroke

Heat stroke is life threatening, and because a high percentage of individuals who experience heat stroke die, immediate medical attention is critical when symptoms first appear. Heat stroke, like heat exhaustion, is also a result of prolonged exposure to hot temperatures, restricted fluid intake, or failure of temperature regulation mechanisms of the body. However, the severity of impact on the body is much greater with heat stroke.

Demographics

Heat disorders are harmful to people of all ages, but their severity is greatest in young children and the elderly. Young children are at risk because, in relation to their weight, they have a large surface area of skin through which to lose water. In addition, until about age two, children's kidneys are not able to concentrate urine and preserve body fluids as efficiently as adult kidneys. The elderly also often have reduced kidney function or underlying diseases, or take medications that make them more vulnerable to dehydration. In healthy adults, heat stroke and heat exhaustion often affect athletes, firefighters, construction workers, factory workers, and anyone who exercises heavily and/or wears heavy clothing in hot, humid weather. Obese individuals and those with poor circulation or who take medications to reduce excess body fluids (diuretics) can be at risk when conditions are hot and humid.

Causes and symptoms

Heat cramps

Heat cramps are painful muscle spasms caused by the excessive loss of electrolytes due to heavy perspiration. The correct balance of electrolytes is crucial to many body functions, including muscle contraction and nerve impulse transmission. Heavy exertion in extreme heat and/or restricted fluid intake may lead to heat cramps.

With heat cramps, muscle tissue becomes less flexible, causing pain , difficult movement, and involuntary tightness. Cramps occurs more often in the legs and abdomen than in other areas of the body.

Heat exhaustion

Heat exhaustion is caused by exposure to high heat and humidity for many hours, resulting in excessive loss of fluids and salts through heavy perspiration. The skin may appear cool, moist, and pale. The child may complain of headache and nausea , with a feeling of overall weakness and exhaustion. Dizziness , faintness, and mental confusion are often present, as is a rapid, weak pulse. Breathing becomes fast and shallow. Fluid loss reduces blood volume and lowers blood pressure. Intense thirst and a highly concentrated, reduced volume of deep yellow or orange urine are signs of inadequate fluid intake.

Heat stroke

Before heat stroke occurs, an individual experiences heat exhaustion and the associated symptoms. When the body can no longer maintain a normal temperature, heat exhaustion escalates and becomes heat stroke. Heat stroke is a life-threatening medical emergency that requires immediate life-saving measures.

Heat stroke is caused by overexposure to extreme heat, resulting in a breakdown of the body's heat regulating mechanisms. Body temperature reaches a dangerous level. An individual with heat stroke has a body temperature higher than 104°F (40°C), and possibly as high as 106°F (41.1°C).

Other symptoms of heat stroke include mental confusion with possible combativeness and bizarre behavior, staggering, and faintness. The pulse becomes strong and rapid (160–180 beats per minute). The skin takes on a dry and flushed appearance. There is often very little perspiration. The individual can quickly lose consciousness or have convulsions.

When to call the doctor

The doctor should be called when the child shows any symptoms of heat exhaustion of if he or she has been exposed to heat and dehydrating conditions and has a body temperature of over 102°F (38.9°C). Emergency medical services should be called immediately if the individual has any symptoms of heat stroke or is having difficulty breathing.

Diagnosis

Diagnosis of heat cramps usually involves observation of symptoms such as muscle cramping and thirst. Diagnosis of heat exhaustion or heat stroke, however, may require a healthcare worker to review the child's medical history, document symptoms, and obtain blood pressure and temperature readings. A physician may take blood and urine samples for further laboratory testing. A test to measure the body's electrolytes can also give valuable information about chemical imbalances caused by the heat-related illness.

Treatment

Heat cramps

The care of heat cramps includes placing the child at rest in a cool environment, while giving cool water with a teaspoon of salt per quart, or a commercial sports drink (e.g. Gatorade). Usually, rest and liquids are all that is needed for the child to recover. Mild stretching and massaging of the muscles may be helpful once the condition improves. The child should not take salt tablets, because such a high concentration of salt may actually worsen the condition. When the cramps stop, the person usually can begin light activity again if there are no other signs of illness. The child needs to continue drinking fluids and should be watched carefully for further signs of heat-related illnesses.

Heat exhaustion

The child suffering from heat exhaustion should stop all physical activity and move immediately to a cool place out of the sun, preferably a cool, air-conditioned location. He or she should lay down with feet slightly elevated, remove or loosen clothing, and drink cold (but not iced), slightly salty water or a commercial sports drink. Rest and replacement of fluids and salt is usually all the treatment that is needed, and hospitalization is rarely required. Following rehydration, the child usually recovers rapidly.

Heat stroke

Simply moving the individual experiencing heat stroke to a cooler place is not enough to reverse internal overheating. Emergency medical assistance should be called immediately. While waiting for help to arrive, quick action to lower body temperature must take place.

Immediate treatment involves getting the child to a cool place, loosening clothing or undressing the person, and allowing air to circulate around the body. The next step is to wrap the child in wet towels or clothing, and place ice packs in areas with the greatest blood supply. These areas include the neck, under the arm and knees, and in the groin. Once the patient is under medical care, cooling treatments continue as appropriate. The child's body temperature is monitored constantly to guard against overcooling. Breathing and heart rate are monitored, and fluids and electrolytes are replaced intravenously. Anti-convulsant drugs may be given. After severe heat stroke, hospitalization may be necessary and bed rest is recommended for several days.

Prognosis

Prompt treatment for heat cramps is usually very effective, allowing the individual to return rapidly to activity. Treatment of heat exhaustion usually brings full recovery in one to two days. Heat stroke is a very serious condition and its outcome depends upon the general health and age of the individual. Due to the high body temperature resulting from heat stroke, permanent damage to the brain, kidneys, heart, and other internal organs is possible. Heat stroke can be fatal, especially for infants and toddlers.

Prevention

Because heat cramps, heat exhaustion, and heat stroke have a cascade effect, the prevention of the onset of all heat disorders is similar.

• Avoid strenuous exercise when it is very hot.
• Drink plenty of fluids, especially water, and avoid drinking alcoholic beverages; drink frequently, even if not thirsty.
• Wear light and loose-fitting clothing that allows the air to circulate around the body in hot weather.
• Eat lightly salted foods which can help replace salts lost through perspiration.
• Provide proper ventilation of hot areas (fan, open window, air conditioning).
• Use sunblocks and sunscreens with a protection factor of SPF 15 or greater when exposed to direct sunlight.
• Never leave a child locked in a hot environment such as a car, even for a minute.
• Monitor children's activity and fluid intake frequently.
• Offer infants supplemental bottles of water in hot weather.
• Soak bandanas or other clothing in water to wear while working or playing in the heat.
• Wear a hat that allows air circulation (mesh, straw) in the sun.

Parental concerns

Parents need to be especially alert to dehydration and the development of heat disorders in infants who cannot ask for something to drink. Parents need to take the initiative in encouraging children to drink frequently in hot weather. Water or sports drinks are a better choice of liquids than soft drinks.

Before the 1970s, some coaches felt it was good training to limit the amount of fluids athletes drank at practices. As a result, there were 39 documented heat-related deaths in athletes between 1964 and 1973. As the water-electrolyte balance of the body became better understood, most coaches have recognized that water should be freely available during athletic practices and events. As a result, documented heat-related deaths declined substantially in the 1980s. When children participate in athletics, parents need to be aware of the potential for heat disorders and assure that appropriate measures for prevention are taken by coaches.

See also Sunburn .

Resources

BOOKS

American Red Cross. Standard First Aid. St. Louis: Mosby Year Book, 1993.

Larson, David E., ed. Mayo Clinic Family Health Book. 3rd ed. New York: HarperResource, 2003.

Mellion, Morris B. et al. The Team Physicians Hand Book. Philadelphia: Hanley & Belfus, 2001.

WEB SITES

"The Life Secretariat: Heat Disorders." United States Air Force. Available online at" http://www.mindef.gov.sg/life/heatd.htm (accessed March 3, 2005).

Tish Davidson, A.M. Jeffrey P. Larson, RPT