Hyperthermia is defined as a body temperature over 40 °C. Causes include sepsis, toxidromes, medication reactions, and environmental conditions. In sepsis, a dysregulated immunologic response produces fever. In toxidromes, withdrawal syndromes, and medication reactions, dysregulated metabolism generates endogenous heat. Heat-related illnesses arise when thermoregulatory mechanisms cannot adequately compensate for environmental and metabolic heat. Only heat-related illnesses resulting from environmental exposure respond directly to cooling interventions. Heat-related illness encompasses a spectrum of conditions that arise when thermoregulatory mechanisms fail. Heat exhaustion is characterized by elevated core body temperature accompanied by orthostatic hypotension, tachycardia, diaphoresis, and tachypnea. Heat stroke is defined by elevated core body temperature with central nervous system involvement, potentially manifesting as delirium, decreased level of consciousness, or ataxia. Heat-related illness most commonly affects athletes (exertional hyperthermia) but can also occur in hot environments or regions with extreme temperatures (classic hyperthermia). People with impaired thermoregulation or limited coping strategies, such as those at the extremes of age or individuals with comorbidities like obesity, psychiatric disorders, substance use disorders, metabolic disorders, or cardiac conditions, are at higher risk. Most cases in the U.S. occur in patients aged 25 to 64 years. The rising burden of heat-related illness is exacerbated by climate change, as heat waves increase in frequency and intensity. The risk of morbidity and mortality is influenced by heat exposure, individual susceptibility, and population-level factors, including social determinants of health. The definitive treatment for heat-related illness is total body cooling. Conduction and evaporation are the 2 primary modes of heat removal. Ice-water immersion has been shown to be the most effective method. However, logistical and resource constraints often limit its use in the emergency department. This intervention may be provided during athletic events, particularly endurance competitions like marathons, where heat-related illnesses are common. Evaporative cooling using mist and fans is the next most efficient method. Application of ice packs to the groin, axilla, neck, and other areas adjacent to major vessels is less effective. Cooled intravenous fluids have been studied, but evidence remains inconclusive regarding their benefit for neurologic preservation versus potential harm from induced shivering, although they may be considered in select cases. This activity will outline the procedure for evaporative cooling and describe adjunct methods applicable in the emergency department. Commercially available devices designed for cooling include invasive cooling catheters and noninvasive adhesive pads that circulate chilled water. These devices were originally developed for targeted hypothermia following cardiac arrest but may be applied to heat-related illnesses when available. Limited literature directly compares these devices with traditional cooling methods. Antipyretics should not be used in heat-related illness, as they may exacerbate coagulopathy and contribute to organ dysfunction. Dantrolene has not been shown to improve recovery and is not indicated for heat-related illness. Benzodiazepines may serve as an adjunct, primarily to control shivering and agitation. Early recognition and intervention are crucial in managing heat-related illness. Military and sports medicine literature identifies 39 °C as the treatment goal, and achieving this temperature more rapidly is associated with lower patient mortality.
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