Environmental heat diagnoses

Background

• 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

Miliaria

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

• Heat cramps
• Heat edema
• Heat exhaustion
• Heat tetany
• Heat stroke
• Heat syncope
• Miliaria
• Hyperthermia

See also hyperthermia

Evaluation

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

Management

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

Disposition

• 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

• Hyperthermia
• Celsius Fahrenheit Temperature Conversion