Heat-Related Illness in Children in an Era of Extreme Temperatures

After completing this article, readers should be able to:A 12-year-old obese football player finishes his second 2-hour practice on a hot August day. His temperature is 105°F (40.6°C), and he is agitated and confused. His family calls you, his general pediatrician, seeking guidance. What advice do you give?A bystander discovers a 23-month-old infant in the back seat of a minivan on a warm day. She is flushed, fussy, and has vomited. The baby is brought to your community emergency department for further management. What are your next steps?As the planet gets warmer, the incidence of heat-related illness (HRI) and injury is increasing. (1)(2)(3)(4)(5) Among those suffering HRI, children compose almost half (47.6%) of this population. (1) In the pediatric population, the most common forms of heat-related pathology occur in exercising adolescents and in children left unattended in vehicles or excessively warm environments. Pediatricians must effectively counsel caregivers in recognizing the dangers related to heat exposure and preventing dehydration and HRI. When prevention fails, prompt recognition and treatment of HRI become paramount.Heat-related illness refers to a clinical spectrum of disorders resulting from exposure to excessive environmental heat and the body’s inability to effectively regulate heat. Presentation can range from mild (heat rash, heat stress) to severe (heat stroke). Note that tolerance to heat varies by individual. Many factors, including general health, overall conditioning, hydration status, and ability to acclimatize (or adapt over time to change in temperature) play a role in the effect that heat has on the individual.Heat rash and prickly heat are colloquial names for miliaria. It is commonly seen in infants during periods of high heat and humidity. It is an erythematous, papular, or vesicular rash caused by the obstruction of eccrine sweat glands. (6) It may be pruritic and is benign and self-limited. Treatment is supportive and includes wearing light, loose garments and avoiding overheating. (7)Heat edema is a mild form of HRI manifested as swelling of the feet, hands, and other dependent areas. It occurs in unacclimatized individuals as a result of vasodilation and venous pooling. (6) Although more common among the elderly, heat edema can occur in children as well. The body temperature of the individual is normal and the condition is unrelated to heart failure or kidney disease. Treatment is supportive: elevation, compression stockings, and moving to a cooler environment. (7)Heat cramps are due to involuntary contractions of skeletal muscle that occur during or after exercise. (8)(9) The term heat cramps is a misnomer because the heat does not directly trigger cramping, and high-intensity exercise in cold environments (eg, hockey, swimming) can be associated with cramps. A more accurate term is exercise-associated muscle cramping. The spasms are painful and usually involve only the muscle groups actively involved in exercise. (8) They typically occur in the dehydrated, deconditioned, or poorly acclimatized athlete. (10) Risk factors include a history of muscle cramps or previous injury to the muscle, tendon, or ligament; heavy sweating; dehydration; or poor sodium intake before or during exercise. (9) Treatment is supportive: rest, hydration, and static stretching. (6)(8)(9)Heat syncope is also related to vasodilation and venous pooling. It is an orthostatic event that causes brief loss of consciousness and is usually seen in an individual who is standing for a prolonged period or changing positions rapidly in a warm environment. (8) Heat exposure may contribute to the event but is not the causative factor. As with heat edema, body temperature is normal. Treatment is also similar: individuals should be moved to a cooler environment and remain supine until light-headedness has resolved and vital signs have normalized. Hydration status should be assessed while providing the patient with oral or intravenous fluids. (1)Heat stress represents a mild form of HRI. It refers to perceived discomfort and physical strain that result from exposure to heat or a warm environment. Symptoms are typically mild, and core temperature remains within the normal range. (7)Heat exhaustion (also called heat injury) is a moderate illness associated with increase in core temperature (98.6°F–104°F [37°C–40°C]) and symptoms include thirst, headache, weakness, syncope, vomiting, and dizziness. (6) Heat exhaustion is often accompanied by dehydration and heavy sweating. The patient’s vital signs will likely demonstrate tachycardia and hypotension. An important feature of this clinical syndrome is that there is no central nervous system (CNS) dysfunction or end-organ damage. (9) If there are CNS symptoms (headache, slight confusion), they are mild and resolve quickly with cooling and rest. (7)Treatment of heat exhaustion entails cessation of physical exertion, removal of excess clothing and equipment, movement to a cooler environment, and hydration with oral or intravenous fluids. (1) Cooling methods may include taking a cool shower or applying cold compresses. Heat exhaustion may progress to heat stroke if not recognized and managed promptly. (6) When treated promptly and appropriately, however, most patients' symptoms will resolve quickly, and hospital admission is unnecessary. (8)Heat stroke represents the most severe form of HRI and results from thermoregulatory failure. It is a life-threatening condition defined as a core temperature greater than 104°F (>40°C) accompanied by CNS dysfunction in the setting of known heat exposure and/or strenuous exercise. The CNS abnormalities can include agitation, confusion, delirium, or coma. Henceforth, this review focuses on the differential diagnosis, pathophysiology, etiology, diagnosis, management, and prevention of heat stroke.It is important for the clinician to be aware of and distinguish other causes of hyperthermia. Hyperthermia in the form of a fever is a common occurrence in the pediatric population. A fever is a normal physiologic response to infection or inflammation that causes a rise in body temperature. The response is controlled by central thermoregulatory centers in the brain, and the temperature rises, although not usually higher than 105.8°F (41°C), in a neurologically normal host. Fever is often, but not always, accompanied by other signs of infection, illness, or inflammation.Less common causes of hyperthermia include neuroleptic malignant syndrome and malignant hyperthermia. Neuroleptic malignant syndrome is a life-threatening, idiosyncratic reaction in patients taking antipsychotic medications. It is characterized by the clinical triad of hyperthermia, muscle rigidity, and altered mental status in the setting of exposure to dopaminergic agents. Malignant hyperthermia is an inherited condition that occurs in susceptible individuals exposed to inhalational anesthetics and/or succinylcholine. It is characterized by hyperthermia and skeletal muscle rigidity and responds to treatment with dantrolene. (11)Human body temperature is regulated by the anterior hypothalamus and is maintained within a narrow range of 97.7°F to 99.5°F (36.5°C–37.5°C). (8) As the body’s core temperature begins to rise (through exercise or exposure to ambient heat), the body shifts from heat storage to heat dissipation. (10) The body has several processes by which it can thermoregulate, although these processes become increasingly ineffective as ambient temperature increases.Radiation of heat from the body to the environment will occur only if the ambient temperature is below the body temperature. Convection occurs when heat from the body is transferred to cooler air (gas), and conduction occurs when heat is directly transferred from a warmer surface (the body) to a cooler one. Thus, as ambient temperature increases, the primary method of thermoregulation is evaporation. (10) Sweat is vaporized at the skin surface, allowing heat dissipation and cooling.Physiologic changes occur as the core body temperature increases: vasodilation leads to increased heart rate, stroke volume, and cardiac output. Warmer blood moves peripherally to the skin, allowing for sweat production and evaporation. (10) As blood moves from the core to the periphery, visceral perfusion is diminished, most prominently in the kidneys and gut. (2) If exposure to heat is excessive or prolonged, the body is less able to compensate.The critical thermal maximum (CTM) reflects the core body temperature and duration of heat exposure that is lethal to an animal. In humans, the CTM is estimated to be 106.9°F to 107.6°F (41.6°C–42°C) for 1 to 8 hours. (12) Prolonged hyperthermia exceeding the CTM can lead to a dangerous cascade of ischemia, end-organ damage, multisystem organ failure, and potentially death.As the body attempts to cool, high demand on the heart can progress to high-output cardiac failure and cardiogenic shock. Hypotension often develops and is multifactorial. It is commonly due to vasodilation (as part of the thermoregulatory process) as well as hypovolemia (secondary to profuse sweating and insensible losses). In the most severe cases, hypovolemia may also be secondary to cardiogenic shock. Prolonged hypotension will ultimately lead to poor perfusion, ischemic injury, and end-organ damage. In addition, the vascular endothelium is sensitive to heat, and excessive exposure may result in disseminated intravascular coagulation. As vascular and mucosal permeability is altered, cerebral and gut edema may develop. (2)(11)On the cellular level, protective mechanisms against hyperthermia exist; however, exposure to extreme or prolonged heat will result in direct cytotoxic effects to cells as well as activation of various cytokines and inflammatory pathways. Protein denaturation and programmed cell death (apoptosis) will ultimately occur. (2)(11) Because hyperthermia can be life-threatening, it is important for clinicians to understand the thermoregulatory process and the manner in which age and development effect it.It had previously been suggested that pediatric athletes were less capable of effective thermoregulation during exercise; however, newer findings demonstrate this to be false and suggest that, from a physiology standpoint, young athletes are not more susceptible to heat injury. (13) In fact, children are generally not at higher risk for HRI than adults (who tend to have more cardiovascular disease and comorbidities that worsen HRI outcomes). However, there are physiologic and developmental differences unique to children regarding thermoregulation.Children and adolescents take longer to acclimatize to a warm environment than adults. Acclimatization is the process by which an individual adapts to a change in temperature and/or humidity. Physiologic changes that occur during the acclimatization period include increased sweat production, reduced electrolyte losses in sweat, increased skin blood flow during exercise, larger stroke volume, larger plasma volume, increased aldosterone production with decreased urine sodium excretion, and decreased temperature threshold to start sweating. (8)(10) Student athletes should be given 10 to 14 days to acclimatize to new exercise in warm weather. (14) Furthermore, infants and young children are thought to have less effective thermoregulation than adults plus lack developmental capabilities to change their behavior in response to overheating (eg, drink water, remove seat belts or clothing, change environments). (15) Special care must be given to their unique needs during periods of extreme heat.Exposure to heat is the primary etiology of heat stroke. The nature of the exposure allows for further classification of heat stroke into nonexertional (classic) and exertional heat stroke. Nonexertional heat stroke results from exposure to high environmental temperatures in the absence of excessive physical activity. It is most commonly seen with extremes of age (young children and the elderly are at highest risk) during heat waves or extreme heat events. Common scenarios include a child left unattended in a vehicle (vehicular heat stroke) or living in a dwelling without central air-conditioning or climate control. (16) During extreme heat events, air-conditioning has been shown to be a protective factor and is associated with decreased risk of heat-related mortality. (17)(18)In the pediatric population, vehicular heat stroke is not uncommon, with an average of 37 deaths due to vehicular heat stroke per year in the United States during the past 2 decades. Of these vehicular heat stroke deaths, 87% were in children younger than 3 years. (19) A review of 171 deaths from vehicular heat stroke found that fatalities were attributed to children playing in the vehicle (27%) or to children left in the vehicle (73%). (20) In the most common scenario, a parent forgets that the child is in the back of the car and unintentionally leaves him or her in the vehicle. This conceivably happens when a parent deviates from their daily routine. (21)(22) A parent who usually drives straight to work may, on a different day, take his or her infant to day care and then drive to work. Out of habit or absentmindedness, the parent may follow his or her typical routine and go straight to work, leaving the infant in the vehicle unintentionally. In other circumstances, poorly supervised young children may gain access to an unattended vehicle and risk entrapment when they cannot escape from the trunk or vehicle. Finally, a parent may intentionally leave a child unattended in a car not realizing that even short periods in a closed vehicle may cause a serious HRI. (20)(22)It is an all-too-common misconception that vehicle-related HRI can happen only on extremely warm days. In reality, vehicles trap heat from the sun, causing the temperature within the car to rise rapidly. Even on days where the outdoor temperature is mild but sunny, the interior of the vehicle can reach dangerous temperatures. One study demonstrated these findings: on a day with an ambient temperature of 72°F (22.2°C), the interior of a car can reach 117°F (47.2°C) within 60 minutes. Furthermore, 80% of the temperature rise occurs in the first 30 minutes. (15) Cracking the car’s windows does little to alter this effect. Thus, children should not be left alone in cars, even with the windows open. (21) In fact, at the time of this writing, 19 of the states in the United States have made it illegal to leave a child unattended in a vehicle. (23)In to nonexertional heat exertional heat stroke is most common in the and occurs after prolonged strenuous exercise. It may also be seen in and who work in warm often in or heavy protective is estimated that more than high athletes are treated for exertional heat illness are at highest risk for exertional heat stroke among and an average of 2 high football of exertional heat stroke. August is the most common for exertional heat illness to although athletes can be during cooler as well. August has an high incidence of HRI, in part due to high temperatures and in part due to athletes after over the as cell disease and and and can adolescents at higher risk for HRI. that sweating increase loss or increase heat production may thermoregulatory (8)(10) generally deconditioned, dehydrated, or from a illness are risk factors for exertional heat care and should be aware of pediatric risk factors to against exhaustion and heat stroke are clinical defined by hyperthermia after heat that CNS dysfunction altered mental and core body temperature higher than 104°F are heat stroke from heat of the of of exertional and nonexertional heat stroke will usually with clinical however, of heat stroke may also have of end-organ damage. findings of heat stroke and heat exhaustion are in CNS symptoms may as mild but become severe (eg, delirium, and more core temperature is greater than 105.8°F It is important to that core temperature on to care may be less than 104°F if cooling have been heat stroke should remain on the differential for patients with the exposure and clinical even if core temperature is less than 104°F In of skin patients with or nonexertional heat stroke will have skin secondary to prolonged thermoregulatory (8) In patients with exertional heat stroke may have cool, skin or be warm and if they were in exercise or strenuous before stroke must be recognized promptly and treated Treatment is in begins first and with of the patient’s and per emergency activation on the of of core temperature and of cooling should be the next the and have been are the to core body temperature. that body temperature or are not to core temperature and should not be in of a must as as heat stroke is The of cooling is to blood flow from the to the core and to body temperature by the body’s (9) The method of cooling will on the the age of the clothing and should be while cooling is and the child is moved to a children and athletes with exertional heat suggest that (eg, in or an is the and most effective cooling This can be if temperature should be less than and the should be or The body should be when for the and can be by a If are vital signs and temperature should be (eg, (9) athletes with exertional heat illness, it is to cool first and second when If effective cooling cannot be (or if the patient has other emergency department should be although cooling methods should be infants and younger there are regarding and have been patient and regarding In this population, cooling than cooling should be for young children or for children when is include the patient with while to air methods for young and children may include of should be and or the patient in a cold to the or have been shown to be only effective and should be only if there are no (8) The of cooling is to rapidly the core temperature while to The threshold to cooling varies in the and from to the core temperature should be a or (10) vital signs and mental status should also be are to cooling with intravascular or or the and and cooling secondary includes of hydration status and as well as and treatment of of heat stroke. of heat stroke and associated are in should include of end-organ damage. may be for accurate and urine (10) and of should be by the patient’s status, and electrolyte in will of patients should be given a and then are no in the treatment of heat stroke. are not in core temperature due to HRI. which is to malignant hyperthermia, has no role in the of heat stroke. may be in the of heat stroke and should be on a may be to the and to which may be a of heat stroke. and of heat stroke are although it is known that is directly related to quickly cooling is (10) It is also known that of the injury is related to the duration of hyperthermia and the of the temperature. with mild heat stroke generally a with normal with severe heat stroke may but with injury. It is estimated that to of patients with severe heat stroke have moderate or severe and a of at signs include and (10) with higher or are more likely to and death is usually from cardiovascular must be to and patients the dangers of heat As the should clothing and for infants and children with needs who cannot their behavior in response to high environmental temperature or overheating. Special should be to hydration status during periods of high heat and as infants and children with needs may have increased insensible losses that will of water, it to HRI and heat there are prevention that can be should be to leave their child unattended in a vehicle and to car when not in to (21) The has an that caregivers to suggest that the a or in the seat that they are to the back seat before the may also vehicular HRI. has a system to to the back seat the vehicle is may to the of an seat and the the may play a role in are that will the to to vehicles with an system to to the exertional heat stroke various as the of the and the have to management, and prevention of HRI in and their are in the It is important for and caregivers to be with signs and symptoms of HRI as well as preventing these dangerous of athletes should a history and physical to or that may to HRI. should be the of HRI and effective prevention and should that athletes with or or should not be to the should follow for and for (eg, typically occur in during the days of the should acclimatize to warm and increase over 1 to 2 The and duration of physical should increase during this should garments that are and and practice should be made from or to heat (6) garments should be promptly. (10) The of should be in as in should be to and after physical During should have access to and and should be time to (9) hydration as has been shown to increase and 3 for daily is extremely should be for and when temperatures are generally should be in to or if heat or is to be The is an of heat stress that for and The may be as an to environmental a risk of HRI to are that suggest on physical on the (8)(10) When the is not the heat may also be to and event and for cooling should be at events. (9) should be for practice and playing in heat and humidity. An emergency should be in should demonstrate signs or symptoms of heat exhaustion or heat stroke. (9)