Each July, emergency departments across the country see a predictable rise in patients presenting with heat-related illness.Construction workers, outdoor athletes, older adults living without adequate cooling, and children exposed in or near vehicles can all arrive to the hospital within minutes of a single sustained heat event. Heat remains one of the leading weather-related causes of death in the United States, and the public health burden tends to peak during the summer months when prolonged exposure, urban heat islands, and seasonal activities converge. For ED clinicians, the window between presentation and disposition is often the window in which outcome is decided. Heat stroke is one of the few critical illnesses where the speed and quality of cooling at the point of care correlate directly with morbidity and mortality. Patients who arrive on the cooler end of the heat illness continuum can decompensate quickly if recognition is delayed, and the differential for altered mental status with hyperthermia is wide enough that anchoring on a single diagnosis early can be costly. This article reviews the continuum of heat illness, the two clinical phenotypes of heat stroke, evidence-based cooling strategies, the medications and conditions that raise patient risk, and the populations at highest risk during peak summer months.
The Continuum of Heat Illness
Heat-related illness is best understood as a continuum, with progression from mild to life-threatening determined by exposure intensity, duration, hydration status, acclimatization, and underlying medical risk. Recognizing where a patient sits on that continuum at the point of arrival shapes the workup and disposition.
Heat cramps, often involving the large muscle groups of the legs and abdomen, occur in the setting of sodium losses through sweating during sustained physical activity. They are typically self-limited and respond to rest, oral rehydration with electrolytes, and removal from heat exposure.
Heat exhaustion is more clinically significant. Patients present with core temperatures generally below 40°C (104°F), profuse sweating, fatigue, headache, nausea, lightheadedness, and often tachycardia. Mental status is preserved. Treatment includes moving the patient to a cool environment, removing excess clothing, active cooling with evaporative methods or wet towels, and intravenous fluid replacement when oral intake is insufficient or symptoms are severe.
Heat stroke represents the failure of thermoregulation and is defined by core temperature elevation above 40°C (104°F) combined with central nervous system dysfunction. Confusion, ataxia, seizures, and coma can all occur. Heat stroke is a true medical emergency and the only point on the continuum at which delay in cooling materially changes outcome.
The clinical distinction between heat exhaustion and heat stroke is mental status. A patient with a core temperature of 39.8°C who is alert and conversational is managed differently than a patient with a core temperature of 40.2°C who is disoriented and combative. The presence of CNS dysfunction shifts the disposition immediately.
Classic and Exertional Heat Stroke
Heat stroke presents in two clinical phenotypes that share underlying physiology but differ in patient population, risk factors, and onset.
Classic heat stroke typically affects older adults, patients with chronic medical conditions, and individuals taking medications that impair heat dissipation. It tends to develop over days during sustained heat waves and is more common in patients living without adequate cooling. The original NEJM review of classic heat stroke by Bouchama and Knochel outlined the pathophysiology of thermoregulatory failure and the systemic inflammatory response that drives multi-organ dysfunction once core temperatures climb.
Exertional heat stroke develops more acutely in physically active individuals, often young and previously healthy, whose metabolic heat production exceeds the body’s capacity to dissipate it. Football players, military trainees, marathon runners, and outdoor workers are the most commonly affected populations. The more recent NEJM review of heatstroke by Epstein and Yanovich describes the heightened risk of rhabdomyolysis, acute kidney injury, hepatic injury, disseminated intravascular coagulation, and cardiovascular collapse, and emphasizes the critical importance of immediate cooling.
Despite differences in population and trajectory, both phenotypes are governed by the same principle at the point of care: time at elevated core temperature drives organ injury, and aggressive cooling is the single intervention with the strongest evidence to improve outcomes.
Cooling Strategies in the ED
The Wilderness Medical Society’s Clinical Practice Guidelines for the Prevention and Treatment of Heat Illness, most recently updated in 2019, summarize the current evidence on cooling techniques and recommend a tiered approach based on access, patient population, and clinical setting.
Cold water immersion remains the most effective cooling technique for exertional heat stroke, achieving the fastest rates of core temperature reduction documented in the literature. When available, full-body immersion in a tub or stock tank with circulating ice water is the gold standard. The National Athletic Trainers’ Association position statement on exertional heat illnesses recommends cooling to a core temperature of 38.9°C (102°F) before transport, and emphasizes that for exertional heat stroke, “cool first, transport second” is the appropriate approach when immersion is available on site.
Evaporative cooling, with the patient undressed, sprayed with tepid water, and exposed to fans, is widely used in EDs that cannot accommodate immersion. When combined with ice packs to the neck, axillae, and groin, it provides reasonable cooling rates and is often the preferred approach for classic heat stroke patients, particularly older adults who may not tolerate immersion well.
Internal cooling techniques, including cold intravenous fluids, gastric or bladder lavage, and intravascular cooling devices, can supplement external methods in critically ill patients but do not replace effective external cooling as the primary intervention.
Regardless of technique, the practical goal is the same: bring core temperature to approximately 38.9°C (102°F), then stop active cooling to avoid overshoot. Continuous core temperature monitoring, ideally with a rectal or esophageal probe, is essential. Skin and oral temperatures underestimate core temperature in this setting and should not be used to guide cooling decisions.
Medications and Conditions That Raise the Risk
Several classes of medication impair the body’s ability to dissipate heat and increase the risk of heat illness during sustained exposure. Recognition of these patterns matters for two reasons: they shape risk assessment in any patient who presents during a heat wave, and they should inform discharge counseling for patients leaving the department with prescriptions during summer months.
The American Geriatrics Society Beers Criteria, updated in 2023, identifies several of the relevant medication classes as potentially inappropriate in older adults, particularly during periods of environmental heat stress. Categories worth scrutinizing include:
- Anticholinergic medications, which reduce sweating and impair evaporative cooling. This class includes first-generation antihistamines, certain antimuscarinic agents for overactive bladder, tricyclic antidepressants, and some antiemetics.
- Diuretics, which reduce intravascular volume and predispose to dehydration during heat exposure.
- Beta blockers, which blunt the cardiovascular response to heat stress and reduce skin blood flow.
- SSRIs and other psychoactive agents, including antipsychotics, which can interfere with central thermoregulation and may carry an additional risk of neuroleptic malignant syndrome that complicates the differential.
- Stimulants and sympathomimetics, including cocaine, amphetamines, and MDMA, which increase metabolic heat production and have been associated with severe hyperthermia.
Chronic conditions that raise heat illness risk include cardiovascular disease, diabetes, obesity, neurologic conditions that limit mobility or temperature perception, dermatologic conditions that impair sweating, and recent acute illness with fever.
Occupational and behavioral risk factors round out the picture. Outdoor workers, athletes training in early-season heat without adequate acclimatization, military trainees, and unhoused individuals all carry elevated risk during sustained heat exposure.
Pediatric and Older Adult Considerations
The two age groups most vulnerable to heat illness sit at the ends of the spectrum, and for very different reasons.
Children have higher body surface area to mass ratios, lower sweating capacity, and slower acclimatization than adults. Younger children may not recognize or communicate early warning signs of heat illness, and behavioral cues are often the only warning. The American Academy of Pediatrics has emphasized the disproportionate impact of climate-related heat exposure on children’s health, with policy guidance addressing pediatric vulnerability and the role of pediatricians and emergency clinicians in recognition and prevention.
Vehicular heat stroke remains the leading cause of pediatric heat-related death in the United States, with the interior of a parked car reaching dangerous temperatures within minutes even on moderate days. Recognition of this mechanism and a low threshold for evaluation in any child with a relevant history is essential.
Older adults face a different physiology. Thermoregulation, thirst response, skin perfusion, and cardiovascular reserve all decline with age, and chronic medication use further compounds risk. Older patients living alone or in housing without air conditioning are particularly vulnerable during sustained heat events and may present late in the course of classic heat stroke. The mental status changes that define heat stroke can be easily attributed to baseline cognitive impairment, which represents one of the more common diagnostic pitfalls.
For both populations, the admission threshold should be lower. Discharge planning must include a realistic assessment of the environment to which the patient is returning. A heat-stable disposition is not a safe disposition for a patient returning to a third-floor apartment without cooling in the middle of a heat advisory.
Heat as a Predictable Emergency
Heat illness is among the most predictable critical presentations in emergency medicine. Forecasts give days of warning. The National Weather Service’s HeatRisk and heat safety resources provide daily, location-specific information on heat-related health risk that can inform staffing, supply, and surge planning in EDs that face recurring heat events. Many regions now experience heat waves with sufficient regularity that operational preparedness around cooling supplies, dedicated cooling spaces, and rapid-immersion capability is increasingly part of standard ED operations.
The clinical fundamentals remain durable. Recognize where the patient sits on the heat illness continuum. Differentiate classic from exertional presentations. Cool early and aggressively, using the most effective technique available. Identify the medications and conditions that increase risk. Pay particular attention to children and older adults, and to the environments they return to. Document core temperature accurately and reassess frequently during cooling.
Heat-related illness is unusual in emergency medicine in that it offers a clear path from recognition to intervention to outcome. Patients who are cooled quickly do well. Patients in whom cooling is delayed do not. July is a fitting moment to revisit the protocols, equipment, and clinical habits that determine which side of that line each patient lands on.
References
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Bouchama, A., & Knochel, J. P. (2002). Heat stroke. New England Journal of Medicine, 346(25), 1978-1988. https://doi.org/10.1056/NEJMra011089
By the 2023 American Geriatrics Society Beers Criteria® Update Expert Panel. (2023). American Geriatrics Society 2023 updated AGS Beers Criteria® for potentially inappropriate medication use in older adults. Journal of the American Geriatrics Society, 71(7), 2052-2081. https://doi.org/10.1111/jgs.18372
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Epstein, Y., & Yanovich, R. (2019). Heatstroke. New England Journal of Medicine, 380(25), 2449-2459. https://doi.org/10.1056/NEJMra1810762
Lipman, G. S., Gaudio, F. G., Eifling, K. P., Ellis, M. A., Otten, E. M., & Grissom, C. K. (2019). Wilderness Medical Society clinical practice guidelines for the prevention and treatment of heat illness: 2019 update. Wilderness & Environmental Medicine, 30(4S), S33-S46. https://doi.org/10.1016/j.wem.2019.07.001
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