Heat-Related Illnesses

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Chapter 66 Heat-Related Illnesses

Kathy Palmer, MD

1 Explain the four methods of heat loss from the body

image Conduction by direct contact of the body with objects and surrounding air

image Convection to air or liquid that surrounds body tissues

image Evaporation through perspiration

image Radiation of infrared energy directly into the environment

Ewald MB, Baum CR: Environmental emergencies. In Fleisher GR, Ludwig S, Henretig FM (eds): Textbook of Pediatric Emergency Medicine, 5th edition, Philadelphia, Lippincott Williams & Wilkins, 2006, pp 1017–1021.

2 What environmental conditions predispose to heat-related illnesses?

High ambient temperature and humidity. Once ambient temperature equals or exceeds skin temperature, conduction, convection, and radiation cease to be effective methods of heat dissipation. The only remaining method of heat loss is evaporation (perspiration). Evaporative heat loss begins to decrease once ambient humidity reaches 75% and is minimal once it reaches 90–95%. In the presence of high ambient temperature and humidity, the body can no longer dissipate heat by any mechanism and the core temperature inevitably rises, causing heat-related illnesses.

Ewald MB, Baum CR: Environmental emergencies. In Fleisher GR, Ludwig S, Henretig FM (eds): Textbook of Pediatric Emergency Medicine, 5th edition. Philadelphia, Lippincott Williams & Wilkins, 2006, pp 1017–1021.

3 What is the best type of clothing to prevent heat-related illness?

Light-colored clothing permeable to moisture but impervious to radiant heat from the environment allows heat loss by evaporation but prevents heat gain by radiation from the environment. During longer periods of activity, dry clothes should replace sweat-saturated garments.

4 Why are children at a greater risk for heat-related illnesses than adults?

image Larger ratio of body surface area to mass (greater heat exchange with the environment)

image Higher set point (change in rectal temperature at which sweating starts)

image Greater endogenous heat production

image Lower output of sweat

image Greater thermoregulatory impairment by dehydration

image Blunted thirst response in comparison with adults

Neonates are at greatest risk because they have poorly developed thermoregulatory mechanisms and depend on others to remove them from a hot environment and provide adequate hydration.

Bytonski JB: Heat illness in children. Curr Sports Med Rep 2:320–324, 2003.

5 What situations or activities are associated with a high risk for heat-related illnesses in children?

image Saunas, steam rooms, whirlpools, and hot tubs: Severe hyperthermia secondary to rapid conduction of heat from the water

image Unventilated automobiles in the hot sun: Temperatures can reach 60° C within 15 minutes when a car is left in the sun at 30–40° C.

6 What patient factors predispose to heat-related illnesses?

1 Conditions associated with excessive fluid loss (fever, gastrointestinal infection, diabetes insipidus, and diabetes mellitus)

2 Suboptimal sweating (spina bifida)

3 Excessive sweating (some cyanotic heart disease)

4 Diminished thirst (cystic fibrosis)

5 Inadequate drinking (mental retardation, young children who rely on others for liquid intake)

6 Abnormal hypothalamic thermoregulatory function (anorexia nervosa, prior heat-related illness)

7 Obesity

American Academy of Pediatrics Committee on Sports Medicine and Fitness: Climactic heat stress and the exercising child and adolescent. Pediatrics 106:158–159, 2000.

7 What is the most important risk factor for heat-related illnesses?

Dehydration. Participants in sports associated with intentional weight loss immediately before competition (wrestlers, jockeys, and boxers) are at increased risk for heat-related illnesses. Attempts at rapid oral rehydration after weighing in are not successful at preventing heat-related illness because plasma volumes remain decreased despite return to normal body weight.

8 What problems are considered minor heat emergencies?

Heat edema, heat cramps, and heat syncope.

Pratt A: Putting the chill on heat-related illness Contemp Pediatr June:23–28, 2005.

9 What is heat edema? How is it treated?

Heat edema is mild swelling of the feet and ankles during the summer months, usually worse in the first few days of exposure. No treatment is necessary except reassurance.

10 What are heat cramps? How are they treated?

Heat cramps are painful involuntary spasms of major muscle groups during or immediately after exercise in a hot environment. Symptoms may be exacerbated by excessive intake of hypotonic fluids during exercise. Heat cramps are treated by placing the victim in a cool environment and replacing fluid and salt losses. Oral electrolyte solutions (or 1 tsp of table salt in 500 mL of water) are appropriate for milder cases; IV fluids (20 mL/kg of 0.9 normal saline solution) are used in more severe cases. Appropriate conditioning, acclimation, and adequate hydration can prevent heat cramps.

Bytonski JB: Heat illness in children. Curr Sports Med Rep 2:320–324, 2003.

11 What is heat syncope? How is it treated?

A syncopal event caused by prolonged standing in hot weather is seen most often in military recruits and marching band members. High temperatures, vasodilatation, and relative dehydration are the precursors. Heat syncope is treated by placing the victim in a recumbent position in a cool environment and administering oral fluids. Minimal knee bending can prevent future syncopal events while standing at attention for prolonged periods.

Lugo-Amador NM: Heat-related illness. Emerg Med Clin North Am 22:315–327, 2004.

12 What is the difference between heat exhaustion and heat stroke?

Heat exhaustion and heat stroke are a continuum of heat-related illnesses that occur when the body’s heat loss mechanisms are overwhelmed or insufficient to respond to environmental demands. Heat exhaustion is the less severe of the two and is believed to represent reversible heat overload, whereas heat stroke is characteristically associated with irreversible tissue damage.

13 What are the clinical characteristics of heat exhaustion? How is it treated?

Heat exhaustion is a precursor to heat stroke and therefore warrants vigorous treatment. Symptoms include temperature elevation, nausea, vomiting, headache, excessive sweating, hyperventilation, and intense fatigue. Victims have a relatively normal mental status except for mild confusion, clumsiness, unsteadiness, dizziness, or weakness. Tachycardia, tachypnea, and orthostatic hypotension are often present. Hemoconcentration, hypernatremia, hyperchloremia, and urinary concentration are common. Treatment includes allowing the victim to rest in a cool environment, administering oral fluids (IV fluids in more severe cases), external cooling (e.g., fans, ice, sponge baths), and monitoring for signs of heat stroke. An adolescent or adult should consume 1–2 L of cold water over 2–4 hours. Cooling to the point of shivering should be avoided because shivering increases the body’s endogenous heat load.

Glazer JL: Management of heatstroke and heat exhaustion. Am Fam Phys 71:2133–2142, 2005.

14 What are the two variants of heat stroke?

Classical and exertional.

Classical heat stroke presents with coma, elevated temperature, and hot, dry skin. Heat stroke is often seen in epidemic proportions during heat waves when victims are constantly exposed to elevated temperature and humidity for several days without relief. The typical pediatric victim initially becomes dehydrated; if left untreated over a period of days, symptoms progress to lethargy, coma, and ultimately death. The disease process may advance more rapidly if the child is exposed to extremely high temperatures (e.g., if left in an unventilated car in the summer).

Exertional heat stroke most often is associated with strenuous physical activity in hot weather; poorly conditioned and poorly acclimated patients are at the highest risk. Exertional heat stroke most often presents with an acute deterioration of mental status.

Ewald MB, Baum CR: Environmental emergencies. In Fleisher GR, Ludwig, S, Henretig FM (eds): Textbook of Pediatric Emergency Medicine, 5th edition, Philadelphia, Lippincott Williams & Wilkins, 2006, pp 1017–1021.

15 What are the central nervous system manifestations of heat stroke?

Central nervous system dysfunction can be manifested in many ways, including a sense of impending doom, headache, dizziness, weakness, confusion, euphoria, gait disturbance, combativeness, seizures, posturing, and coma. The early clinical symptoms are sometimes overlooked because they often are perceived to be the normal result of exertion. Often the severity of the problem is realized only when the victim collapses suddenly.

Glazer JL: Management of heatstroke and heat exhaustion. Am Fam Phys 71:2133–2142, 2005.

16 Describe the clinical characteristics of heat stroke

Shock (hypovolemic), altered mental status, and rectal temperature > 40° C are suggestive but not diagnostic for heat stroke. Sweating may or may not be present. Dehydration, tachycardia, tachypnea, and postural or frank hypotension may be seen. In more severe cases, seizures, posturing, or coma is present.

Ewald MB, Baum CR: Environmental emergencies. In Fleisher GR, Ludwig S, Henretig FM (eds): Textbook of Pediatric Emergency Medicine, 5th edition, Philadelphia, Lippincott Williams & Wilkins, 2006, pp 1017–1021.

17 How is heat stroke treated?

The goals of therapy are to restore intravascular volume and to lower core body temperature. Treat the victim as you would any other patient with shock:

1 Address airway, breathing, and circulation while moving the victim to a cool, shaded environment.

2 Obtain large-bore IV access, and place a Foley catheter to monitor urine output.

3 Attach the patient to a cardiac monitor and supply supplemental oxygen.

4 Administer crystalloid solutions (normal saline or lactated Ringer’s) to address hypovolemia or hypotension.

5 Begin external cooling as soon as possible.

6 Order initial laboratory studies: blood gas, complete blood count, clotting studies, electrolytes, glucose, renal and liver function tests, and electrocardiography. Be prepared to treat arrhythmias and seizure activity and to correct electrolyte imbalances.

7 Cooling should be continued until the core temperature reaches 38.5° C.

8 More severe cases may require central venous pressure monitoring and inotropic support. α-Adrenergic drugs should be avoided because they decrease skin perfusion and limit heat dissipation.

9 All victims of heat stroke require hospitalization, the majority in an intensive care setting.

Lugo-Amador NM: Heat-related illness. Emerg Med Clin North Am 22:315–327, 2004.

18 List the possible complications of heat stroke

Acidosis, electrolyte imbalance, adynamic ileus, dysrhythmias, shivering, seizures, rhabdomyolysis, disseminated intravascular coagulation, renal failure, hepatic damage, permanent neurologic sequelae, and death.

Glazer JL: Management of heatstroke and heat exhaustion. Am Fam Phys 71:2133–2142, 2005.

19 Explain heat acclimatization

Acclimatization describes the body’s physiologic adaptation to tolerate activity in a hot, humid environment. Acclimatized people demonstrate increased ability to sweat and improved conservation of total body sodium. Well-conditioned athletes acclimate to hot weather more efficiently than their poorly conditioned peers. People who are not acclimatized are at greater risk for heat-related illnesses.

American Academy of Pediatrics Committee on Sports Medicine and Fitness: Climactic heat stress and the exercising child and adolescent. Pediatrics 106:158–159, 2000.

20 How long does it take to acclimate to a hot, humid environment?

Eight to 12 days in adults. Children require a gradual increase in duration and intensity of activity over 10–14 days. The American Academy of Pediatrics recommends “as many as 8 to 10 exposures (30–45 minutes each) to the new climate to acclimatize sufficiently. Such exposures can be taken at a rate of one per day or one every other day.” Athletes who plan to compete during the midday should include periods of training during the warmer midday hours.

American Academy of Pediatrics Committee on Sports Medicine and Fitness: Climactic heat stress and the exercising child and adolescent. Pediatrics 106:158–159, 2000.

21 What is the best way to provide external cooling for victims of heat-related illnesses?

The victim’s clothing should be removed to allow maximal skin exposure and heat dissipation. The most traditional method of cooling involves covering the patient with sheets or towels that have been immersed in ice water and then allowing a fan to blow across them; sheets and towels should be changed frequently to keep them cool. Ice baths or ice water baths have been advocated by some authors, but they are impractical in more severe cases of heat stroke requiring cardiopulmonary resuscitation or defibrillation.

Evaporative cooling can be accomplished by spraying the skin with cool water and allowing a fan to blow across the moistened skin. Cooling by evaporation is more efficient than ice water baths in reducing core body temperature.

Alternative methods of cooling that require special training or equipment include peritoneal lavage with cold fluids, cardiopulmonary bypass, ice water enemas, and bladder and gastric lavage.

Stewart C, Ruddy R: The spectrum of heat illness in children. Pediatr Emerg Med Rep 4:41–52, 1999.

22 What methods of cooling are ineffective or harmful?

image Alcohol baths: Children are susceptible to toxic absorption of alcohol through the skin

image Antipyretics: Not successful in decreasing temperatures secondary to heat-related illnesses

Stewart C, Ruddy R: The spectrum of heat illness in children. Pediatr Emerg Med Rep 4:41–52, 1999.

23 How can heat-related illnesses be prevented?

Physical activity should be modified in the face of high ambient temperature and humidity. Athletes should be well hydrated before initiating physical activity and should continue to consume cold water throughout the exercise period and after exercise has been completed to avoid dehydration. Clothing should be lightweight and light-colored, with as much skin exposed as possible to allow evaporative dissipation of heat. Athletes should participate in a preseason conditioning program and allow a period of acclimation when exercising in the hot summer months.

Glazer JL: Management of heatstroke and heat exhaustion. Am Fam Phys 71:2133–2142, 2005.

KEY POINTS FOR HEAT-RELATED ILLNESS

1 Heat-related illness can be fatal but is most importantly PREVENTABLE.

2 Heatstroke is the third most common cause of exercise-related deaths in U.S. high schools (following head injuries and cardiac disorders).

3 Adequate hydration before, during, and after exercising is one of the key elements in prevention of heat-related illness.

4 Children may require as long as 2 weeks to acclimate safely to exercising in a hot climate.

24 What is the Wet Bulb Globe Temperature (WBGT) Index?

The WBGT index is an attempt to standardize the effects of heat, humidity, and solar radiation on the body. It reflects the influence of ambient temperature, humidity, and solar radiation. Recommendations for modification of physical activity in hot weather are based on the WBGT index.

The U.S. Armed Forces WBGT index can be found on the following website: www.usariem.army.mil/heatinjury.htm.

25 What are the current recommendations for modification of activity in hot, humid weather?

See Table 66-1.

Table 66-1 Restraints on Activities at Different Levels of Heat Stress*

image

American Academy of Pediatrics Committee on Sports Medicine and Fitness. Climactic heat stress and the exercising child and adolescent. Pediatrics 106:158–159, 2000.

26 How much fluid is required to maintain hydration during exercise?

Exercising athletes may lose 2–3% of body weight before they become thirsty. Athletes should drink 8 ounces of cold water 10–15 minutes before exercising and consume an additional 8–12 ounces every 20–30 minutes during exercise. Heavier athletes require more fluid; smaller athletes may require less. When beginning training in the heat, athletes should weigh themselves before and after a workout to ensure adequate postexercise rehydration—a pint of water for every pound lost. Maintenance of clear, unconcentrated urine output indicates adequate hydration.

27 Why is even mild dehydration and heat exposure a dangerous combination in children?

Children who are dehydrated experience an excessive increase in core body temperature when exposed to a hot environment compared to their well-hydrated peers and similarly hydrated adults.

American Academy of Pediatrics Committee on Sports Medicine and Fitness. Climactic heat stress and the exercising child and adolescent. Pediatrics 106:158–159, 2000.

28 How much fluid should a child drink while exercising in a hot climate?

They should begin the exercise period well hydrated, and periodic drinking should be enforced during the exercise period. For every 20 minutes of exercise, 150 mL of cold tap water or a flavored salted beverage should be consumed for a 40-kg child (250 mL for a 60-kg adolescent). The child should be encouraged to drink even if he or she is not thirsty.

American Academy of Pediatrics Committee on Sports Medicine and Fitness. Climactic heat stress and the exercising child and adolescent. Pediatrics 106:158–159, 2000.

29 What are the benefits of flavored sports drinks?

Flavored sports drinks were shown to increase voluntary drinking by 90% over plain water. Adding salt to sports drinks also enhances thirst. The recommended concentration is 15–20 mmol NaCl/L or 1 gm of NaCl in 2 pints of water.

American Academy of Pediatrics Committee on Sports Medicine and Fitness. Climactic heat stress and the exercising child and adolescent. Pediatrics 106:158–159, 2000.

WEBSITES

1. The American Red Cross: Heat-related illness www.redcross.org/services/hss/tips/heat.html

2. Centers for Disease Control and Prevention: Tips for preventing heat-related illness http://www.bt.cdc.gov/disasters/extremeheat/heattips.asp

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