Environmental heat diagnoses

(Redirected from Heat Emergencies)


  • Heat related illnesses includes a wide range diagnoses from benign heat rash to heat stroke.
  • Dehydration and salt depletion affect thermoregulation by reducing the body's ability to increase the cardiac output needed to dissipate the heated blood
  • Cardiovascular disease and use of drugs that impair cardiac function can result in increased susceptibility to heat illness

Types of heat dissipation

  • Conduction: heat exchange between two surfaces in contact (placing ice pack in axilla)
  • Convection: heat exchange between a surface and a fluid (fanning)
  • Radiation: transfer of heat between body and environment through electromagnetic waves (reliant on temperature gradient)

Heat Illness Etiology

All types are due to inadequate thermoregulation

  1. Classic Heat Illness
    • Occurs without physical exertion
  2. Exertional
    • Preceded by physical activity

Clinical Features

Man with signs of heat exhaustion, including copious sweating.

Heat Illness Types

  1. Heat cramps
    • Muscle cramps due to electrolyte depletion
  2. Heat syncope
    • Prolonged standing +vasodilation + volume loss → decreased central venous return → decreased CO→ decreased cerebral perfusion pressure
  3. Heat exhaustion (temperature usually < 40°C)
    • headache, n/v, weakness, vertigo, no CNS dysfunction
    • Water depletion: inadequate fluid replacement to match fluid loss (sweat)
    • Salt depletion: large volume of fluid loss is replaced with water (with inadequate salt)
  4. Heat stroke (temperature usually > 40°C)
    • Similar to heat exhaustion plus CNS dysfunction (seizure, AMS), transaminitis, DIC, rhabdomyolysis

Differential Diagnosis

Environmental heat diagnoses

See also hyperthermia


  • Clinical diagnosis
  • Evaluate for alternate etiologies of hyperthermia if no clear exposure


  1. Heat cramps
    • Mild: oral electrolyte solution
    • Severe: IV NSS
  2. Heat syncope
    • Supine position
  3. Heat exhaustion
    • Mild: oral fluid replacement
    • Severe: IV fluid replacement and replete electrolytes as needed
  4. Heat stroke
    • ABCs
    • Rapid cooling
    • IVF, replete electrolytes
    • Benzos: for seizures and shivering


  • Heat stroke requires admission
  • Other conditions can be discharged after improvement with treatment
  • Do not use antipyretic agents (their use in heat illness has not been evaluated)

See Also