Heat-related illnesses in children encompass a wide range of disease processes—from minor conditions such as heat rash to life-threatening thermoregulatory emergencies such as heatstroke. Physiological differences in children compared to adults make them particularly susceptible to illnesses caused by heat exposure.
Pediatric heat-related illnesses can usually be prevented if appropriate precautions are taken (see “Taking Steps to Prevent Heat-Related Illnesses” box). In lieu of prevention, early recognition and treatment of heatstroke in children may drastically reduce life-threatening complications related to multisystem organ dysfunction. Management of heatstroke rests primarily on prompt initiation of rapid cooling measures and evaluation for organ dysfunction.
Case Scenarios
Case 1
An obese 10-year-old boy was brought to the ED by emergency medical services (EMS) during the first week of youth football tryouts. It was a hot day in late August, with 100% humidity and temperatures over 95°F. The patient, who weighed approximately 240 lb, was trying out for football but had no previous athletic-conditioning experience. Despite his obesity, he had been generally healthy and only took a stimulant medication for attention-deficit/hyperactivity disorder (ADHD).
At approximately noon, the boy collapsed on the field and had a seizure. When the EMS technicians arrived, they administered a dose of intramuscular (IM) midazolam. Although his seizure ceased, he remained obtunded and was intubated. A rectal temperature revealed a temperature of 105.8°F and paramedics noted that while the patient felt hot, he was no longer sweating. While en route to the ED, EMS technicians removed the patient’s football uniform; placed a fan in front of him; and sprayed cool water on him in an effort to lower his body temperature. At the time of arrival to the ED, his rectal temperature was 104.9°F.
Case 2
A previously healthy 3-month-old female infant was brought to the ED by EMS after she was accidentally left in a car on a summer day with a temperature of 90°F and 100% humidity. The infant’s father said that while running errands, he had forgotten his daughter was in the car and had left her in the rear facing backseat car carrier for approximately 10 minutes. When he returned to the car, he found his daughter awake but crying inconsolably. She had sweated through her clothes, vomited, and felt very hot, so he called 911. Her initial rectal temperature was 102.2°F, and her clothes were removed as she was being transported in an air-conditioned ambulance to the ED for further evaluation. Once undressed, she was noted to have an erythematous rash with multiple papules and pustules on her trunk.
Epidemiology
From 2006 to 2010, an average of 668 heat-related deaths per year occurred among people of all ages in the United States. Of these deaths, approximately 7% occurred in children younger than age 4 years (2.5% in those younger than age 1 year and 4.5% in those age 1-4 years). These figures have remained relatively stable over the last 10 years.1,2 Adolescents are particularly at risk for overexertion, and heatstroke is the third leading cause of death in young athletes, after traumatic and cardiac causes.3 As may be expected, most heat-related deaths (76%) occur in the southern and western regions of the United States.
Pathophysiology of Heat-Related Illnesses
The hypothalamus is the main control center for temperature homeostasis. As the core temperature rises due to either metabolic or environmental causes of heat, the hypothalamus primarily acts on the autonomic nervous system to engage mechanisms of heat dissipation.4 Evaporation of sweat is believed to be the most important mechanism of heat dissipation in humans; however, this method becomes less effective when humidity levels are above 75%.5 Radiation allows heat to transfer from the skin to the air, but is reliant on a temperature gradient. Conduction can allow heat to transfer to a cooler object through physical contact (as seen with cold-water immersion), while convection utilizes air movement to transfer heat (as illustrated by fanning).6
Thermoregulation is disrupted when the body is unable to balance metabolic heat production and heat dissipation. Heat dissipation mechanisms are easily overwhelmed when a person is exposed to excessive heat from the environment. The resulting stress from hyperthermia can directly injure cells, leading to a cytokine storm and endothelial injury. Heat can cause proteins to denature and cells to undergo apoptosis, which, if severe, can result in multisystem organ dysfunction.7
Physiological Differences in Children
Several physiological differences in children compared to adults compromise their ability to manage heat exposure. Thermoregulation in infants is less developed secondary to an immature hypothalamus; therefore, they are less able to utilize compensatory mechanisms to dissipate heat.8 In addition, infants and young children have a decreased sweating capacity, which makes evaporative cooling less effective.9 Children also produce more endogenous heat per kilogram than adults, which is believed to be secondary to a higher basal metabolic rate. They have less blood volume than adults, which decreases their ability to transfer warm blood into the periphery in order to cool the central core. Lastly, children have a higher surface area-to-body mass ratio, which causes increased heat absorption. All of these factors ultimately result in a slower rate of acclimatization in children compared to adults.10