INTRODUCTION — The manifestations, evaluation, and management of heat illness in children other than heat stroke will be reviewed here. Heat stroke in the pediatric patient and heat illness in the adult patient are discussed separately. (See "Heat stroke in children" and "Severe nonexertional hyperthermia (classic heat stroke) in adults".)
PATHOPHYSIOLOGY — Body temperature is maintained within a narrow range by balancing heat load with heat dissipation. The body's heat load results from both metabolic processes and absorption of heat from the environment. Evaporation is the principal mechanism of heat loss in a hot environment, but this becomes ineffective above a relative humidity of 75 percent. The other major methods of heat dissipation — radiation (emission of infrared electromagnetic energy), conduction (direct transfer of heat to an adjacent, cooler object), and convection (direct transfer of heat to convective air currents) — cannot efficiently transfer heat when environmental temperature exceeds skin temperature (typically 35ºC or 95ºF).
Children differ from adults with respect to their anatomical and physiologic response to heat stress. These differences translate into a potentially greater susceptibility for severe heat illness in children, especially infants and young athletes [1,2]. The pathophysiology of heat illness in children is discussed in greater detail separately. (See "Heat stroke in children", section on 'Pathophysiology'.)
CLINICAL MANIFESTATIONS AND TREATMENT — All heat-related illnesses result from excessive heat exposure caused by an increased environmental heat burden, an inability of the body to dissipate endogenous heat, or a combination of these two factors. There are many manifestations of heat-related illnesses (table 1).
Miliaria (heat rash) — Miliaria is a common finding in newborns, especially in warm climates. It may also occur in older individuals. Accumulation of sweat beneath eccrine sweat ducts results from obstruction by keratin at the level of the stratum corneum. Pruritus is common. Several types of lesions may result:
●Miliaria crystallina is characterized by small thin-walled vesicles resembling dewdrops without inflammation (picture 1).
●Miliaria rubra ("heat rash," "prickly heat") occurs when the obstructed sweat leaks into the dermis and causes a localized inflammatory response, resulting in small groups of pruritic, erythematous papules and pustules (picture 2).
●Miliaria pustulosa also results from localized inflammation; it consists of pustules with an erythematous base similar to miliaria rubra.
●Miliaria profunda is papular or papulopustular and skin colored.
This benign condition typically resolves without specific treatment when the individual is placed in a cooler environment with associated measures to reduce sweating, such as light, loose clothing, and cool baths.
On occasion, nonspecific treatments may be used for pruritus (eg, calamine lotion, anhydrous lanolin, wet compresses, topical corticosteroids), and oral antihistamines (eg, cetirizine). Superinfection of miliaria (eg, impetigo) rarely occurs and should be treated with antistaphylococcal antibiotics (eg, topical mupirocin or oral cephalexin) . (See "Impetigo", section on 'Treatment' and "Miliaria".)
Heat edema — Heat edema is most commonly seen in unacclimatized older persons. This mild form of heat illness involves the hands and feet and is caused by vasodilation with pooling of interstitial fluid in dependent extremities . Core body temperature remains normal.
Management consists of moving to a cooler environment, elevation of the extremities, and use of compression stockings . Diuretics should be avoided in these patients.
Heat syncope — Heat syncope refers to dizziness, orthostatic hypotension, and syncope that occur in patients with heat-related peripheral vasodilation and venous pooling . Syncope often occurs in patients who remain standing after significant exertion or who rapidly change position during exertion. When this occurs in the exercising child, this condition is sometimes referred to as “exercise-associated collapse.” These patients have a normal or near-normal core body temperature and a rapid return to normal mental status once they are supine.
Treatment includes moving the patient to a cooler environment and administering intravenous normal saline (initial infusion 20 mL/kg; maximum initial dose 1 L) or providing oral rehydration with salt-containing liquids until the patient no longer has orthostatic vital sign changes. While orthostatic, the patient should maintain a supine position until volume repletion has occurred.
Heat cramps — Heat cramps refer to painful muscular cramping that may occur during or after exertion in hot environments. The cramping commonly involves the large muscle groups of the legs (eg, quadriceps, gastrocnemius), abdomen, or arms. Patients may have a normal or elevated core body temperature. However, core body temperature does not exceed 40ºC (104ºF). Heat cramps are sometimes referred to as exercise-associated muscle cramps when they occur during or after exercise. (See "Exertional heat illness in adolescents and adults: Epidemiology, thermoregulation, risk factors, and diagnosis", section on '"Heat cramps" (exercise associated muscle cramps)'.)
The management of heat cramps is discussed separately. (See "Exertional heat illness in adolescents and adults: Management and prevention", section on '"Heat cramps"'.)
Heat cramps differ from heat tetany because they are not associated with circumoral paresthesias and do not typically cause upper extremity spasms.
Heat tetany — Heat stress may cause hyperventilation that may result in respiratory alkalosis, positive Chvostek or Trousseau sign, laryngospasm, or spontaneous carpopedal spasm (heat tetany) . Affected patients often complain of circumoral paresthesias. Core body temperature may be normal or elevated up to 40ºC (104ºF).
Treatment consists of moving the patient to a cooler environment, which typically causes the hyperventilation to cease and the symptoms to abate. Consideration must be given to other serious etiologies, such as status asthmaticus, metabolic acidosis, pain, central nervous system disorders, and drug intoxication, and these diagnoses must be excluded.
Occasionally, additional measures may be necessary:
●In those patients with persistent hyperventilation and symptoms despite cooling, placement of a partial rebreather oxygen mask with oxygen flow set below 5 L per minute allows the patient to rebreathe carbon dioxide without causing hypoxia and may assist in terminating the hyperventilation.
Heat exhaustion — Patients with heat exhaustion have known heat exposure and an elevated core body temperature between 37ºC (98.6ºF) and 40ºC (104ºF). Additional symptoms include:
●Sweating (especially when associated with exercise)
●Syncope with prompt return of normal mental status
●Normal mental status or mild confusion that responds rapidly (within 30 minutes) to cooling
●Signs of mild to moderate dehydration
There is some overlap of symptoms between heat exhaustion and heat stroke (table 2). While the distinction between heat exhaustion and heat stroke is sometimes unclear, children with elevated body temperature and CNS abnormalities should be treated as victims of heat stroke, given the significant morbidity and mortality associated with this condition. (See "Heat stroke in children", section on 'Hospital management'.)
While most patients with heat exhaustion have normal electrolytes, some patients may have increased serum sodium due to hypotonic fluid losses, or decreased serum sodium due to excess salt losses in the sweat; hyponatremia may be exacerbated by hypotonic fluid replacement. Thus, these patients should receive salt-containing oral fluids (eg, flavored sports drinks such as Gatorade) or intravenous normal saline.
Prehospital treatment — Prompt recognition of heat exhaustion is important because some cases progress to heat stroke. Unfortunately, many patients who develop heat stroke do not have antecedent heat exhaustion. Children with symptoms of heat exhaustion should stop exercising immediately and be moved to a cooler environment (eg, natural shade, air-conditioned vehicle, air-conditioned building). Excess clothing should be removed, and the patient should be given chilled salt-containing liquids (eg, flavored sports drinks) to drink. Most patients with mild heat exhaustion respond to these measures and do not require further care [6-9].
Hospital management — Patients who do not respond to prehospital measures or who initially present with dehydration or mental status changes warrant hospital evaluation. In addition to maintaining a cool ambient environment, such patients should undergo the following care:
●Measurement of rectal temperature
●Intravenous bolus of normal saline (20 mL/kg; maximum initial infusion 1 L)
●Measurement of serum electrolytes and treatment of any sodium abnormalities (see "Treatment of hypovolemia (dehydration) in children in resource-abundant settings", section on 'Therapy according to serum sodium')
Children with mild confusion should have rapid clearing of their mental status within 30 minutes of initiation of treatment for heat exhaustion. Children with altered mental status on arrival to the hospital and a history of exertion in warm weather should be treated for heat stroke. (See "Heat stroke in children".)
Disposition — Most children with heat exhaustion who require hospital care recover fully within a few hours and can be discharged home. Rarely, patients with heat exhaustion may need to be admitted to the hospital for correction of significant electrolyte abnormalities.
PREVENTION OF HEAT ILLNESS — Successful prevention of heat-related morbidity and mortality requires recognition of the potential for heat stress posed by environmental conditions and appropriate adaptation to elevated ambient temperature during outside activities occurs. Specific actions include:
●Activity restriction – Clinicians should support efforts to curtail organized athletic activities and warn the public of danger when weather conditions pose a significant risk for heat injury. Up to 70 percent of the risk for heat illness is attributable to excess humidity, followed by elevated solar radiation (20 percent) and increased temperature (10 percent). Risk for heat stress can be identified using either the wet bulb globe temperature (WBGT) or the heat index [10,11]. The WBGT takes into account all three weather factors when assessing environmental conditions. However, the heat index, which only takes into account humidity and temperature, is more easily obtainable (table 3 and table 4).
Specific activity restrictions are suggested for given levels of heat index or WBGT (table 5) [11,12]. Recommended adaptations include more hydration breaks, more frequent player substitutions during organized competition, ensuring a shaded area for rest, scheduling of practices or games earlier or later in the day when heat conditions abate, or canceling athletic activities when the risk of severe heat illness is too high. When activity is allowed, complete rest and a cool-down period after a period of strenuous exercise may reduce the risk of increased heat strain during a subsequent exercise period in some children . Children who are currently ill or recovering from an illness (especially fever and/or gastrointestinal illnesses) should avoid or limit exercise .
●Maintenance of hydration – Scheduled hydration breaks with strong encouragement for drinking is very important in children because they are more likely to inadequately replenish fluid losses during prolonged exercise when dehydrated compared to adults [14,15]. General guidelines suggest 100 to 250 mL (three to eight ounces) every 20 minutes for 9 to 12 year old children and up to 1 to 1.5 L (34 to 50 ounces) per hour in adolescents assuming normal pre-activity hydration . (See "Heat stroke in children", section on 'Pathophysiology'.)
Flavoring water by adding both carbohydrates and sodium chloride increases fluid intake by as much as 90 percent versus offering unflavored water [16-18].
The adequacy of hydration can be measured by comparing pre- and post-activity dry weight. One rule of thumb is to consume 240 mL (8 ounces) of fluid for every pound lost during the event . Athletes with persistent weight loss of 2 percent or more should be withheld from activity since unreplaced fluid losses over consecutive days of exercise markedly increase the risk for heat illness.
●Appropriate clothing – Children should wear a single layer of absorbent, loose fitting clothing to maximize convective heat loss. Light colors help reduce absorption of solar radiation .
●Acclimatization – Heat acclimation provides the best protection against heat exhaustion and heat stroke, but this takes repeated exposures to heat. The number and duration of exposures necessary for acclimatization varies by age. For example, an older adolescent may become acclimatized after four successive days of limited heat exposure. In contrast, a young school age child typically needs up to 14 days to achieve the same physiologic endpoint [10,11,19]. In general, acclimatization should occur over 7 to 14 days with progressively increasing intensity and duration of physical activity . (See "Heat stroke in children", section on 'Pathophysiology'.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Heat illness in children" and "Society guideline links: Exertional heat illness".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Heat stroke (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Pathophysiology – All heat-related illnesses result from excessive heat exposure caused by an increased environmental heat burden, an inability of the body to dissipate endogenous heat, or a combination of these two factors. Children are at greater risk for severe heat illness, especially infants and young athletes. (See 'Pathophysiology' above.)
●Clinical manifestations and treatment – The clinical manifestations and treatment of minor heat illness (eg, miliaria [heat rash], heat edema, heat syncope, heat cramps, and heat tetany), heat exhaustion, and heat stroke are summarized in the tables (table 1 and table 2). (See 'Clinical manifestations and treatment' above.)
Prompt recognition of heat exhaustion is important because some patients will progress to heat stroke. Patients who do not respond to prehospital measures or who initially present with dehydration or mental status changes warrant hospital evaluation and management for potential heat stroke. (See "Heat stroke in children", section on 'Hospital management'.)
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