Hyperthermia

Description

• 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)

• 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

• 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

Etiology

• 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