Pediatric Heat-Related Illnesses

Environmental Factors

Several environmental risk factors predispose children to heat-related illnesses. Infants are completely dependent on their caregivers for hydration and environmental protection from the heat. Infants who are over-bundled or left in a hot car are particularly at risk for heat-related illnesses.¹¹ Older children are at risk for sports-related overexertion and typically must depend on permission from a coach or supervising adult to hydrate or take a break from exercise. Lastly, medications such as stimulants frequently prescribed for ADHD or medications with anticholinergic properties (secondary to decreased sweating) can predispose children to heat intolerance.¹²

Minor Heat-Related Illnesses

Heat-related illnesses range from benign conditions (eg, heat rash) to life-threatening processes (eg, heatstroke).

Miliaria Rubra

There are several forms of miliaria. Miliaria rubra, also known as heat rash or prickly heat, is a common, benign manifestation of heat exposure in infants and young children. A combination of heat exposure and obstructed sweat glands results in a pruritic, erythematous rash with papules and pustules (Figure). This is often seen in areas of friction from skin rubbing against skin or clothing.¹³

Heat Edema/Heat Cramps

Heat edema is another benign process related to heat exposure that generally occurs in older adults but can also occur in children. It is the result of peripheral vasodilation as the body attempts to shunt warm blood to the periphery.¹⁴ Heat cramps are a common manifestation in young athletes exercising in hot, summer conditions. Although benign, the cramps are very painful spasms that often affect large muscle groups, particularly in the legs, such as the calves, quadriceps, and hamstrings. There is conflicting data regarding the underlying cause of heat cramps. Many believe there is a significant component related to dehydration, while others attribute the cramps to fatigue or a combination
of the two.¹⁵

Heat Syncope

Heat syncope secondary to peripheral vasodilation, and venous pooling occurs as the body attempts to dissipate heat by transferring warm blood to the periphery. Relative dehydration plays a role in heat syncope, which is often precipitated by a rapid change in positioning during exercise, such as moving from a sitting to standing position. Heat syncope usually improves after the patient is supine, and children with heat syncope do not have an elevation in core body temperature.¹⁴ Some patients who experience heat syncope, however, may also have heat exhaustion.

Heat Exhaustion

Heat exhaustion occurs in patients with a known heat exposure. As opposed to the previously described processes, heat exhaustion is characterized by a body temperature elevated up to 104°F. Heat exhaustion is often accompanied by diffuse, nonspecific symptoms such as tachycardia, sweating, nausea, vomiting, weakness, fatigue, headache, and mild confusion. Dehydration often plays a significant role in heat exhaustion, but in contrast to heatstroke (described in the following section), mentation is normal, or there is a transient, mild confusion.¹⁶

Heatstroke

Heatstroke is observed in patients with a known heat exposure who have a temperature greater than 104°F accompanied by central nervous system (CNS) dysfunction.¹⁴ The CNS dysfunction involves an alteration in mental status manifested by slurred speech, ataxia, delirium, hallucinations, or seizure activity. In severe cases, obtundation or coma may result in airway compromise.¹⁷ Vital signs are unstable, and tachycardia and hypotension are often present. Patients with heatstroke may stop sweating, although the absence of sweating is not required for the diagnosis. Other nonspecific findings such as vomiting and diarrhea are common.⁶

The hallmark of heatstroke is multisystem organ dysfunction, which is caused by heat-induced tissue damage resulting in a systemic inflammatory response.¹⁸ Since the pediatric brain is particularly sensitive to temperature extremes, cerebral edema and herniation are potential complications of heatstroke.¹⁷ Damage to myocardial tissue, coupled with dehydration and systemic vasodilation, results in hypotension and poor systemic perfusion.¹⁹ Muscle breakdown causes rhabdomyolysis that can lead to kidney failure and hepatic injury. Degradation of clotting factors disrupts the clotting system and can cause disseminated intravascular coagulation (DIC).²⁰ Damage to the mucosal lining of the intestines may result in ischemia and massive hematochezia.²¹

Heatstroke is classified as either nonexertional or exertional. Nonexertional heatstroke occurs most frequently in younger children who are exposed to a hot environment, such as an infant left in a car on a warm day. Exertional heatstroke occurs primarily in children exercising on a hot day, such as young athletes.⁶

Due to its significant morbidity and mortality, heatstroke is the most concerning manifestation of excessive heat exposure. The mortality rate for children with heatstroke is significantly lower than for adults; however, approximately 10% of children with heatstroke will not survive,²² and 20% will have long-term neurological disabilities, including permanent impairment in vision, speech, memory, behavior, and coordination.²³