Heat Illness: Heat Exhaustion and Heat Stroke
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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
- System(s) affected: endocrine/metabolic, nervous, hepatic, hematologic
- Synonym(s): heat illness; heat injury; hyperthermia; heat collapse; heat prostration
Elderly persons are more susceptible.
Children are more susceptible.
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
- Poor acclimatization to heat
- Poor physical conditioning
- Salt or water depletion
- 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)
- 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
- Disseminated intravascular coagulation (DIC)
- Hepatocellular necrosis