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Heat Disorders

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 (160180 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.

KEY TERMS

Convulsions Also termed seizures; a sudden violent contraction of a group of muscles.

Electrolytes Salts and minerals that produce electrically charged particles (ions) in body fluids. Common human electrolytes are sodium chloride, potassium, calcium, and sodium bicarbonate. Electrolytes control the fluid balance of the body and are important in muscle contraction, energy generation, and almost all major biochemical reactions in the body.

Rehydration The restoration of water or fluid to a body that has become dehydrated.

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" <www.mindef.gov.sg/life/heatd.htm> (accessed March 3, 2005).

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

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"Heat Disorders." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Encyclopedia.com. 25 Jul. 2017 <http://www.encyclopedia.com>.

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"Heat Disorders." Gale Encyclopedia of Children's Health: Infancy through Adolescence. . Retrieved July 25, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/heat-disorders

Heat Disorders

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 regulation mechanisms of the body. Disorders of heat exposure include heat cramps, heat exhaustion, and heat stroke (also called sunstroke). Hyperthermia is the general name given to heat-related illnesses. The two most common forms of hyperthermia are heat exhaustion and heat stroke, which is especially dangerous and requires immediate medical attention.

Description

Heat disorders are harmful to people of all ages, but their severity is likely to increase as people age. Heat cramps in a 16-year-old may be heat exhaustion in a 45-year-old and heat stroke in a 65-year-old. The body's temperature regulating mechanisms rely on the thermal regulating centers in the brain. Through these complex centers, the body tries to adapt to high temperatures by adjusting the amount of salt in the perspiration. Salt helps the cells in body tissues retain water. In hot weather, a healthy body will lose enough water to cool the body while creating the lowest level of chemical imbalance. 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. If the body loses too much salt and fluids, the symptoms of dehydration can 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 think of heat cramps as a warning sign to 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. It often affects athletes, firefighters, construction workers, factory workers, and anyone who wears heavy clothing in hot humid weather.

Heat stroke

Heat exhaustion can develop rapidly into heat stroke. Heat stroke can be life threatening and because the percentage of victims dying from heat stroke is very high, immediate medical attention is critical when problems first begin. 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.

Causes and symptoms

Heat cramps

Heat cramps are painful muscle spasms caused by the excessive loss of salts (electrolytes), due to heavy perspiration. The muscle tissue becomes less flexible, causing pain, difficult movement, and involuntary tightness. Heavy exertion in extreme heat, restricted fluid intake, or failure of temperature regulation mechanisms of the body may lead to heat cramps. This disorder occurs more often in the legs and abdomen than in other areas of the body. Individuals at higher risk are those working in extreme heat, elderly people, young children, people with health problems, and those who are unable to naturally and properly cool their bodies. Individuals with poor circulation and who take medications to reduce excess body fluids can be at risk when conditions are hot and humid.

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 individual may complain of headache and nausea with a feeling of overall weakness and exhaustion. Dizziness, faintness, and mental confusion are often present, as is rapid and weak pulse. Breathing becomes fast and shallow. Fluid loss reduces blood volume and lowers blood pressure. Yellow or orange urine often is a result of inadequate fluid intake, along with associated intense thirst. Insufficient water and salt intake or a deficiency in the production of sweat place an individual at high risk for heat exhaustion.

Heat stroke

Heat stroke is caused by overexposure to extreme heat, resulting in a breakdown in the body's heat regulating mechanisms. The body's temperature reaches a dangerous level, as high as 106°F (41.1°C). An individual with heat stroke has a body temperature higher than 104°F (40°C). Other symptoms include mental confusion with possible combativeness and bizarre behavior, staggering, and faintness.

The pulse becomes strong and rapid (160-180 beats per minute) with the skin taking on a dry and flushed appearance. There is often very little perspiration. The individual can quickly lose consciousness or have convulsions. Before heat stroke, an individual suffers from heat exhaustion and the associated symptoms. When the body can no longer maintain a normal temperature, heat exhaustion becomes heat stroke. Heat stroke is a life-threatening medical emergency that requires immediate initiation of life-saving measures.

Diagnosis

The diagnosis of heat cramps usually involves the observation of individual symptoms such as muscle cramping and thirst. Diagnosis of heat exhaustion or heat stroke, however, may require a physician to review the medical history, document symptoms, and obtain a blood pressure and temperature reading. The physician may also 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 individual at rest in a cool environment, while giving cool water with a teaspoon of salt per quart, or a commercial sports drink. Usually rest and liquids are all that is needed for the patient to recover. Mild stretching and massaging of the muscle area follows once the condition improves. The individual should not take salt tablets, since this may actually worsen the condition. When the cramps stop, the person can usually start activity again if there are no other signs of illness. The individual needs to continue drinking fluids and should be watched carefully for further signs of heat-related illnesses.

Heat exhaustion

The individual 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. She or he should then lay down with feet slightly elevated, remove or loosen clothing, and drink cold (but not iced), slightly salty water or 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 person usually recovers rapidly.

Heat stroke

Simply moving the individual afflicted with heat stroke to a cooler place is not enough to reverse the internal overheating. Emergency medical assistance should be called immediately. While waiting for help to arrive, quick action to lower body temperature must take place. Treatment involves getting the victim to a cool place, loosening clothes or undressing the heat stroke victim, and allowing air to circulate around the body. The next important step is wrapping the individual in wet towels or clothing, and placing 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 may continue as appropriate. The victim's body temperature will be monitored constantly to guard against overcooling. Breathing and heart rate will be monitored closely, and fluids and electrolytes will be replaced intravenously. Anti-convulsant drugs may be given. After severe heat stroke, bed rest may be recommended for several days.

Prognosis

Prompt treatment for heat cramps is usually very effective with the individual returning to activity thereafter. Treatment of heat exhaustion usually brings full recovery in one to two days. Heatstroke is a very serious condition and its outcome depends upon general health and age. Due to the high internal temperature of heat stroke, permanent damage to internal organs is possible.

KEY TERMS

Convulsions Also termed seizures; a sudden violent contraction of a group of muscles.

Electrolytes An element or compound that when melted or dissolved in water dissociates into ions and is able to conduct an electrical current. Careful and regular monitoring of electrolytes and intravenous replacement of fluid and electrolytes are part of the acute care in many illnesses.

Rehydration The restoration of water or fluid to a body that has become dehydrated.

Prevention

Because heat cramps, heat exhaustion, and heat stroke have a cascade effect on each other, the prevention of the onset of all heat disorders is similar. Avoid strenuous exercise when it is very hot. Individuals exposed to extreme heat conditions should drink plenty of fluids. Wearing light and loose-fitting clothing in hot weather is important, regardless of the activity. It is important to consume water often and not to wait until thirst develops. If perspiration is excessive, fluid intake should be increased. When urine output decreases, fluid intake should also increase. Eating lightly salted foods can help replace salts lost through perspiration. Ventilation in any working areas in warm weather must be adequate. This can be achieved as simply as opening a window or using an electric fan. Proper ventilation will promote adequate sweat evaporation to cool the skin. Sunblocks and sunscreens with a protection factor of 15 (SPF 15) can be very helpful when one is exposed to extreme direct sunlight.

Resources

OTHER

Griffith, H. Winter. "Complete Guide to Symptoms, Illness & Surgery." ThriveOnline. http://thriveonline.oxygen.com.

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heat exposure

heat exposure Although the origins of human life were in the tropical regions, modern man is better able to cope with cold environments than with extreme heat. The skin and subcutaneous tissues of the body can function normally over a wide temperature range, and the temperature of the skin will generally follow the temperature of the surrounding environment. The deeper tissues, and especially the brain, however, must be maintained within a few degrees of the normal body temperature of 37°C if optimum function is to be maintained and irreversible damage prevented. Exposure to a high ambient temperature is a major challenge to the body's ability to keep its temperature within the optimum working range.

Heat is exchanged between the body and its surrounding environment by physical transfer involving conduction, convection, and radiation. When skin temperature is higher than the environmental temperature, heat is lost by these mechanisms, but at high environmental temperatures, heat is gained. Heat exchange can be regulated to some degree by regulating the skin blood flow, which alters the effective insulation layer between the deep tissues and the surface, but behavioural mechanisms, including alterations in the amount of clothing worn and control of the environmental temperature, are more effective. Heat is constantly produced by the metabolic reactions occurring within the body. These are relatively inefficient, and about 75% of the energy appears as heat: this is about the same level of efficiency as the internal combustion engine. At rest, the rate of heat production is low (about 60 W — roughly equivalent to the heat output of a small domestic light bulb), but this rises dramatically during exercise, and the average marathon runner produces more than 1 kW of heat (similar to the output of a small electric fire). When the ambient temperature is low, this can be lost to the environment by physical transfer without any large change in deep body temperature.

When the ambient temperature is high, heat is gained from the environment by physical transfer, and metabolic heat production continues to add to the heat load. Heat loss is promoted by increasing the rate of blood flow to the skin: this allows skin temperature to rise and reduces the thermal gradient, reducing the rate of heat gain. In order to prevent a catastrophic rise in body temperature, an additional heat loss mechanism is invoked as body temperature begins to rise. This involves evaporation of water from the body surface, and active secretion of sweat onto the skin surface will be initiated. The latent heat of vaporization of water is high, and evaporation of this water is an effective way of removing large amounts of heat from the body surface. Water is also lost by evaporation from the respiratory tract, but this is much less important in humans than it is in those animals which have thick coats of hair or wool, as such coats prevent evaporation from the skin by restricting air movement and allowing the air to become saturated with water vapour. A similar problem arises when the humidity of the air close to the skin is high: this is why a hot, humid climate feels more uncomfortable than a hot, dry environment.

At rest, low sweat rates are sufficient to maintain body temperature, but the sweat rate rises dramatically during exercise to balance the increased rate of heat production by the exercising muscles. Industrial workers in hot environments, or atheletes competing in hot climates, can sweat at rates approaching 3 litres/hour. Prolonged exposure to these conditions results in dehydration, and there is a need for fluid replacement if the work is to be sustained. Some of the water lost in sweat is derived from the blood plasma, with the remainder coming from the spaces between and within the body cells. Large sweat losses cause the blood volume to fall by 10% or even more. The reduced blood volume challenges the body's ability to continue to supply sufficient blood flow to the working muscles to provide oxygen and nutrients and to remove waste products, including heat, as well as to supply a high rate of blood flow to the skin to carry heat to the body surface where it can be lost. Heart rate will increase in an attempt to maintain the cardiac output, but eventually skin blood flow will fall, and body temperature will rise.

If body temperature is allowed to rise above about 40°C, a variety of symptoms of heat illness will appear. These include nausea, headache, and dizziness, which should be seen as warning signs. A core temperature of about 42°C or more will result in loss of consciousness, circulatory collapse, and eventually coma and death. The brain, liver, and kidneys, and the blood clotting mechanisms, appear to be particularly sensitive to rises in temperature. The danger of heat illness is obviously increased when both temperature and humidity are high, and is greatest when exercise has to be performed in these conditions. There have been many famous examples of athletes in endurance events collapsing in the later stages of an event, and these collapses normally occur only when the weather is unusually hot. The case of Dorando Pietri, who fell to the track close to the end of the 1908 Olympic Games Marathon held in London, is well known: Pietri was assisted to his feet, and staggered to the finishing line, only to be disqualified on the grounds that he had received assistance during the race.

Sweat contains a variety of salts (especially sodium chloride) as well as a large number of different organic molecules, and replacement of these salts as well as of water is necessary when large sweat losses are incurred. Humans have a limited appetite for salt compared with many animals, but it is normal to feel the need to add extra salt to food when sweat losses are high. Drinks taken to maintain hydration should contain small amounts of sugar and salt to stimulate water absorption in the intestine: this is the basis of the formulation of oral rehydration solutions developed for the treatment of the excessive rates of water loss caused by infectious diarrhoea. Sports drinks used by athletes are formulated along the same principles to achieve effective fluid replacement. The thirst mechanism is not normally sufficient to ensure an adequate rate of fluid to balance the sweat loss, and a conscious effort to drink beyond the level dictated by thirst must be made when sweating rates are high.

On repeated exposure to heat, the body adapts to increase its thermal tolerance. This is achieved by lowering the temperature threshold for the onset of sweating and increasing the sensitivity of the sweating mechanism so that a greater sweat rate is achieved for any given level of body temperature. There is also a more even distribution of sweating over the body surface, ensuring an effective rate of evaporation while minimizing the amount of sweat that drips from the body surface without evaporating. The salt content of the sweat is reduced to compensate for the increased sweating rate, allowing conservation of electrolytes to occur. These adaptations begin within one or two days of exposure to the heat, and the degree of adaptation is related to the amount of heat strain experienced. Adaptations occur more rapidly and more completely if exercise is performed during periods of heat exposure: passive exposure to heat is less effective. Adaptation is essentially complete after about 10–15 consecutive days of exposure to exercise in the heat. After adaptation, heart rate will be lower at any given level of thermal stress, and exercise tolerance is greatly increased. Even after a comprehensive programme of heat acclimatization, however, exercise performance remains impaired relative to that which can be achieved in cool conditions. On returning to a cool environment, the beneficial changes accompanying adaptation are gradually reversed.

R. J. Maughan

Bibliography

Maughan, R. J. and and Shirreffs, S. M. (1998). Fluid and electrolyte loss and replacement in exercise. In Oxford textbook of sports medicine (ed. Harries, Williams, Stanish, and Micheli), 2nd edn pp.97–113. Oxford University Press, New York.
Sutton, J. R. (1994). Physiological and clinical consequences of exercise in heat and humidity. In Oxford textbook of sports medicine, (ed. Harries, Williams, Stanish, and Micheli) pp. 231–8. Oxford University Press, New York.
Wenger, C. B. (1988). Human heat acclimatization. In Human performance physiology and environmental medicine at terrestrial extremes, (ed. K. B. Pandolf, M. N. Sawka, and R. R. Gonzalez) pp. 153–98. Cooper Publishing Group, Carmel.


See also body fluids; metabolism; sweating; temperature regulation.

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Heat Disorders

HEAT DISORDERS

DEFINITION


Heat disorders are a group of illnesses caused by prolonged exposure to hot temperatures, restricted fluid intake, or failure of the body's ability to regulate its temperature. The general term used for heat disorders is hyperthermia (pronounced hi-per-THUR-mee-uh). The three most common forms of hyperthermia are heat exhaustion, heat stroke, and heat cramps.

DESCRIPTION


Hyperthermia can cause harm to people of all ages. But its effects are more serious with increasing age. The conditions that cause heat cramps in a teenager may cause a more serious form of hyperthermiaheat exhaustionin a middle-aged person. Those same conditions may cause even more serious effects in an older person, a form of hyperthermia known as heat stroke.

The human body functions normally only within a very narrow range of temperatures close to 98.6°F (37°C). If the body gets much warmer or much colder than 98.6°F, health problems develop. Raising or lowering the body temperature by only a few degrees can cause death in a short period of time.

The body's temperature control center is in the brain. It senses changes in internal and external temperatures. It determines the changes that must be made to keep body temperature at 98.6°F. It then relays instructions to the body's cells to make these changes.

One method the body uses to cool down is perspiring (sweating). Perspiration is the loss of water from the skin. Body heat provides the energy needed to evaporate water from the skin. The more a person perspires, the cooler the body becomes.

However, excessive perspiration can cause problems. The body may lose too much water. It may become dehydrated. Dehydration can cause a variety of medical problems.

Heat Disorders: Words to Know

Electrolytes:
Chemicals that occur naturally in the body and that maintain the proper balance of fluids in the body.
Hyperthermia:
The general name for any form of heat disorder.

Heat Cramps

Heat cramps are the least serious form of hyperthermia. They are the first sign that the body is having difficulty with increased temperature. Heat cramps are a warning sign that more serious problems may soon develop.

Heat Exhaustion

Heat exhaustion is more serious than heat cramps. The condition may be caused when a person is exposed to high temperatures for a long period of time. Or the body may become dehydrated, or its temperature regulation system may begin to fail. Heat exhaustion is a common problem among athletes, firefighters, construction and factory workers, and anyone who wears heavy clothing in hot weather.

Heat Stroke

Heat stroke is the most serious form of hyperthermia. The condition can cause death in a short period of time. Heat stoke often results in death. The conditions that lead to heat stroke are the same as those that cause heat exhaustion. However, those conditions cause more serious symptoms in the case of heat stroke.

CAUSES


The primary cause of all types of hyperthermia are prolonged exposure to hot temperatures, restricted fluid intake, or failure of the body's ability to regulate its temperature. The three forms of hyperthermia are caused by progressively greater exposure to heat.

SYMPTOMS


Symptoms for the different types of hyperthermia vary. The longer one is exposed to heat, the more serious the symptoms of hyperthermia become.

Heat Cramps

At relatively warm temperatures, the body begins to perspire. Perspiration results in the loss of water. The body slowly becomes dehydrated. Dehydration leads to heat cramps.

As heat cramps develop, muscle tissue becomes less flexible. It becomes more difficult and more painful to move. Muscles in the legs are most frequently affected. A person may find it difficult to walk or maintain his or her balance. Young children, the elderly, and people with circulation problems are more likely to be affected by heat cramps.

Heat Exhaustion

After hours in a hot environment, perspiration increases and body temperature rises. The skin may appear cool, moist, and pale. Other symptoms of heat exhaustion include headache, nausea, exhaustion, and a general sense of weakness. Before long, dizziness, faintness, and mental confusion develop.

Breathing becomes rapid and shallow. The urine of a person with heat exhaustion is likely to be dark yellow or orange.

Heat Stroke

Under the most extreme conditions, the body's temperature regulation system may begin to fail. The brain is no longer able to send messages to the rest of the body telling it how to cool off. Heat stroke may occur after the body temperature has reached 104°F (40°C). At this point, the patient may become mentally confused and aggressive. He or she may begin to stagger and feel faint.

During heat stroke, a patient's pulse rate may reach 160 to 180 beats per minute. The skin appears to be dry and flushed. There is very little perspiration. At this point, the patient needs immediate medical attention. Without care, he or she may die in a matter of hours.

DIAGNOSIS


Most cases of hyperthermia can be diagnosed easily. The two key factors are the patient's visible symptoms and recent personal history. A tennis player who collapses while playing a game, for example, may be suspected of having hyperthermia. Testing that person's temperature, heart rate, and other vital factors may confirm the diagnosis quickly.

Blood and urine tests can also be used to confirm a diagnosis of hyperthermia. In any form of hyperthermia, the balance of chemicals in blood and urine changes. Laboratory tests can detect these changes and confirm the presence of hyperthermia.

TREATMENT


The first steps in treating any form of hyperthermia include:

  • Moving the patient to a cooler location.
  • Providing the patient with cool water.
  • Giving the patient liquids that contain electrolytes.

Electrolytes are chemicals that occur naturally in the body and that maintain the proper balance of fluids in the body. The usual liquids given a patient are salt water that contains a low concentration of salt, or a sports drink such as Gatorade.

The patient should not be given salt tablets. The concentration of salt in tablets is too high for the body to absorb. Salt tablets can make a case of hyperthermia more serious, rather than improving it.

The above steps are often sufficient to treat most cases of heat cramps and heat exhaustion. Massage of leg muscles can also offer relief from the pain and soreness of heat cramps. Patients with heat exhaustion should be made to lie down with their feet elevated.

Cases of heat stroke require emergency treatment by trained medical personnel. While waiting for this help, some first aid measures can be taken. Ice packs should be placed around the neck, under the arms and knees, and in the groin. Medical treatment may involve intravenous feeding of fluids and electrolytes. Bed rest is often necessary for many days.

PROGNOSIS


Prompt treatment of heat cramps and heat exhaustion is usually successful. Patients recover in a matter of hours or, at most, a day or two. Heat stroke poses more serious problems. Prognosis depends on the patient's age and general health. In the most serious cases, heat stroke can lead to permanent damage to internal organs, and even death.

PREVENTION


The general rules for avoiding any form of hyperthermia are the same. One should avoid strenuous exercise when it is very hot. Wearing light, loose-fitting clothing can also help. An important factor in preventing hyperthermia is consumption of sufficient amounts of liquids. The warmer it becomes and the more active a person is, the greater the body's need for liquids. Caffeine and alcohol should be avoided in hot conditions because they can contribute to dehydration, increasing the risk of hyperthermia. Eating lightlysalted foods can also help replace electrolytes lost during perspiration.

FOR MORE INFORMATION


Books

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

Larson, David E., ed. Mayo Clinic Family Health Book, 2nd edition. New York: William Morrow, 1996.

Morris, M., M. Walsh, and Shelton G. Walsh. The Team Physicians Hand Book. Philadelphia: Hanley & Belfus, 1990.

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"Heat Disorders." UXL Complete Health Resource. . Encyclopedia.com. 25 Jul. 2017 <http://www.encyclopedia.com>.

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