Heat-Related Illnesses

Key Features

Essentials of Diagnosis

• Spectrum of preventable heat-related illnesses: heat cramps, heat exhaustion, heat syncope, and heat stroke

• Heat stroke: the most serious disorder, heat stroke, is defined as hyperthermia with cerebral dysfunction in a patient with heat exposure

• Best outcome: early recognition, initiation of rapid cooling, and avoidance of shivering during cooling; delays in cooling result in higher morbidity and mortality in heat stroke victims

• Best choice of cooling method: whichever can be instituted the fastest with the least compromise to the patient

General Considerations

Heat syncope

• Defined as a transient loss of consciousness with spontaneous return to normal mentation

• Results from volume depletion and cutaneous vasodilation with subsequent systemic and cerebral hypotension

• May occur during or immediately following exercise

Heat cramps

• Exercise-associated painful involuntary muscle contractions during or immediately after exercise

• Muscle cramps result from dilutional hyponatremia as sweat losses are replaced with water alone or sometimes from high utilization of aldosterone leading to potassium wasting

Heat exhaustion

• Characterized by dehydration, sodium depletion, or isotonic fluid loss with accompanying cardiovascular changes

• Exhaustion results from prolonged strenuous activity in a hot environment with inadequate water or salt intake

Heat stroke

• A life-threatening medical emergency

• Severe form of heat-related illness resulting in cerebral dysfunction with core body temperature over 40°C

• May present in one of two forms: classic or exertional

  • Classic heat stroke occurs in patients with impaired thermoregulatory mechanisms or in extreme environmental conditions

  • Exertional heat stroke occurs in healthy persons undergoing strenuous exertion in a hot or humid environment

Demographics

• Persons at greatest risk for heat stroke

  • Very young

  • Elderly (age > 65 years)

  • Chronically ill

  • Patients taking medications that interfere with heat-dissipating mechanisms

Clinical Findings

Symptoms and Signs

Heat syncope

• Systolic blood pressure usually < 100 mm Hg; weak pulse

• Skin typically cool, moist

Heat cramps

• Slow, painful skeletal muscle contractions

• Severe muscle spasms last 1–3 min

• Muscles tender, hard, and lumpy; may be twitching

• Skin moist, cool

• Victim alert, with stable vital signs, but may be agitated and complain of focal pain

• Body temperature may be normal or slightly increased

Heat exhaustion

• Rectal temperature > 37.8°C (> 100°F), tachycardia, and moist skin

• Symptoms associated with heat syncope and heat cramps may be present

• Additional symptoms

  • Nausea, vomiting

  • Malaise

  • Myalgias

  • Hyperventilation

  • Thirst

  • Weakness

• Central nervous system symptoms

  • Headache

  • Dizziness

  • Fatigue

  • Anxiety

  • Paresthesias

  • Impaired judgment

  • Psychosis (occasionally)

• Hyperventilation secondary to heat exhaustion can lead ...