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?

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