Heat Illness: Heat Exhaustion and Heat Stroke

Heat Illness: Heat Exhaustion and Heat Stroke is a topic covered in the 5-Minute Clinical Consult.

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  • A continuum of increasingly severe heat illnesses caused by dehydration, electrolyte losses, and failure of the body’s thermoregulatory mechanisms when exposed to elevated environmental temperatures
    • Heat exhaustion is a mild to moderate form of heat illness displaying dehydration type symptoms with a normal to elevated temperature <104°F (1).
    • Heat stroke is characterized by an elevated core temperature >104°F with central nervous system abnormalities and is a true medical emergency (1,2).
  • System(s) affected: endocrine/metabolic, nervous, hepatic, hematologic
  • Synonym(s): heat illness; heat injury; hyperthermia; heat collapse; heat prostration

Geriatric Considerations
Elderly persons are more susceptible.

Pediatric Considerations
Children are more susceptible.

Pregnancy Considerations
Pregnant women may be more susceptible to volume depletion with heat stress.


  • Predominant age: more likely in children or elderly
  • Predominant sex: male = female

  • Depends on intensity of heat; estimate of 20/100,000 persons per season (3)
  • Concern for increasing incidence because ambient environmental temperatures continue to rise
  • Depends on predisposing conditions in combination with environmental factors
  • Roughly 600 deaths per year in the United States

Etiology and Pathophysiology

  • Excess heat has direct cellular toxicity. Excess heat also leads to an imbalance between inflammatory and anti-inflammatory cytokines as well as vascular endothelial damage causing end-organ dysfunction.
  • Interplay between failure of heat-dissipating mechanisms, an overwhelming heat stress, and an exaggerated acute-phase inflammatory response

Risk Factors

  • Poor acclimatization to heat
  • Poor physical conditioning
  • Salt or water depletion
  • Obesity
  • Acute febrile or GI illnesses
  • Chronic illnesses: uncontrolled diabetes mellitus, hypertension, cardiac disease
  • Alcohol and other substance abuse
  • High heat and humidity, poor environmental air circulation
  • Heavy, restrictive clothing
  • Nutritional supplements (e.g., ephedra) (2)
  • Medications (α-adrenergics, anticholinergics, antihistamines, antipsychotics, benzodiazepines, β-blockers, calcium channel blockers, clopidogrel, diuretics, laxatives, neuroleptics, phenothiazines, thyroid agonists, tricyclic antidepressants) (1)

General Prevention

  • The most important factor in preventing heat illness is activity modification and adequate fluid replacement.
  • Allow acclimatization to hot weather through proper conditioning and activity modification.
  • Dress appropriately with loose-fitting, open-weaved, light-colored clothing.
  • Consume a proper volume of fluids, particularly during physical activity in hot environments.
  • Never leave children (or pets) unattended in cars during hot weather.
  • Try to gain access to air-conditioned environments during hot weather.


  • If mental function is not altered and serum chemistries are normal, the prognosis is good and recovery within 24 to 48 hours is typical.
  • The mortality rate for heat stroke (10–80%) is directly related to the duration and intensity of hyperthermia as well as to the speed and effectiveness of diagnosis and treatment (3).


  • May involve failure of any major organ system
  • Cardiac arrhythmias or infarction
  • Pulmonary edema, acute respiratory distress syndrome
  • Coma, seizures
  • Acute renal failure
  • Rhabdomyolysis
  • Disseminated intravascular coagulation (DIC)
  • Hepatocellular necrosis

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