• Range of progressively more severe illnesses due to increasingly overwhelming heat stress
  • Begins with dehydration and electrolyte abnormalities and progresses to thermoregulatory dysfunction and multisystem organ failure
  • Body temperature is maintained within a narrow range by balancing heat production with heat dissipation
  • Oxidative phosphorylation becomes uncoupled and essential enzymes cease to function above 108°F (42°C)

Heat Stroke
  • Core body temp >105°F (40.5°C)
  • Failure of thermoregulatory function leads to severe central nervous system (CNS) dysfunction and multisystem organ failure
  • Classic heat stroke (nonexertional):
    • Occurs in patients with compromised thermoregulation or an inability to remove themselves from a hot environment (e.g., extremes of age, debilitated)
    • Develops over days to weeks, usually during heat waves
    • Severe dehydration, skin warm and dry
  • Exertional heat stroke:
    • Younger, athletic patients with combined environmental and exertional heat stress (e.g., military recruits)
    • Develops over hours
    • Internal heat production overwhelms dissipating mechanisms, often despite persistent sweating

Heat Exhaustion
  • Core temp moderately elevated but usually <104°F (40°C)
  • Fluid and/or salt depletion occurs secondary to heat stress
  • Thermoregulatory function is maintained and CNS function is preserved
  • Variable nonspecific symptoms including malaise, headache, fatigue, and nausea
  • If left untreated, progresses to heat stroke


  • Pre-existing conditions that hinder the body's ability to dissipate heat predispose for heat-related illness:
    • Age extremes
    • Dehydration (incl. gastroenteritis, inadequate fluid intake)
    • Cardiovascular disease (incl. CHF, CAD)
    • Obesity
    • Diabetes mellitus, hyperthyroidism, pheochromocytoma
    • Febrile illness
    • Skin diseases that hinder sweating (incl. psoriasis, eczema, cystic fibrosis, scleroderma)
  • Pharmacologic contributors:
    • Sympathomimetics
    • LSD, PCP, cocaine
    • MAO inhibitors, antipsychotics, anxiolytics
    • Anticholinergics
    • Antihistamines
    • β-blockers
    • Diuretics
    • Laxatives
    • Drug or alcohol withdrawal
  • Environmental factors:
    • Excessive heat/humidity
    • Prolonged exertion
    • Lack of mobility
    • Lack of air conditioning
    • Lack of acclimatization
    • Occlusive, nonporous clothing

Pediatric Considerations
Children are at increased risk of heat illness due to increased body surface area to mass ratio and lower sweat production

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