Description

• A continuum of increasingly severe illness caused by dehydration, electrolyte losses, and failure of 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 (1).
  • Heat stroke is characterized by an elevated core temperature >104°F with central nervous system (CNS) abnormalities and is a true medical emergency (1),(2).
• Can be exertional (related to activity) or non-exertional
• 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.

Epidemiology

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

Incidence

• Depends on intensity of heat; estimate of 20/100,000 persons per season
• Concern for increasing incidence because ambient environmental temperatures continue to rise

Prevalence

• 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, vascular endothelial damage, and 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 prevention. Activity modification and adequate fluid replacement are key preventive measures.
• Allow acclimatization 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.