Heat exhaustion and heatstroke

1. Overview

Both heat exhaustion and heatstroke are heat-related illnesses caused by excessive heat exposure and inadequate thermoregulation, but they differ significantly in severity.

• Heat exhaustion is a milder, reversible form of heat-related illness resulting from fluid and electrolyte depletion.

• Heatstroke is a life-threatening medical emergency characterized by extreme hyperthermia and central nervous system (CNS) dysfunction, requiring immediate treatment to prevent death or permanent disability.

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2. Pathophysiology

The body regulates temperature primarily through sweating and vasodilation. In extreme heat, high humidity, or during strenuous activity, heat production and environmental heat load can overwhelm the body’s capacity for heat dissipation.

• Heat exhaustion: Results from prolonged exposure leading to dehydration, electrolyte imbalance, and decreased plasma volume without significant CNS dysfunction.

• Heatstroke: Failsafe mechanisms collapse, causing core temperature ≥40 °C and systemic inflammatory response, leading to cellular injury, multi-organ dysfunction, and potentially death.

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3. Risk Factors

• High environmental temperature and humidity

• Prolonged physical exertion (especially in hot climates)

• Inadequate fluid intake

• Wearing heavy or non-breathable clothing

• Extremes of age (infants, elderly)

• Chronic diseases (cardiovascular disease, diabetes, renal disease)

• Medications impairing thermoregulation (anticholinergics, diuretics, beta-blockers, antipsychotics)

• Alcohol or drug intoxication

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4. Clinical Features

Heat Exhaustion

• Temperature: Usually ≤40 °C

• Symptoms: Profuse sweating, fatigue, weakness, dizziness, headache, muscle cramps, nausea/vomiting

• Skin: Cool, moist, pale

• Pulse: Rapid, weak

• Blood pressure: May be low (orthostatic hypotension common)

• CNS: No significant dysfunction – may feel lightheaded but remains alert and oriented

Heatstroke

• Temperature: ≥40 °C (often 41–43 °C)

• Symptoms: Sudden onset, hot and often dry skin (may still sweat in exertional type), severe headache, confusion, agitation, seizures, loss of consciousness

• CNS: Prominent dysfunction – delirium, ataxia, seizures, coma

• Cardiovascular: Rapid strong pulse initially; hypotension possible in later stages

• Other signs: Multi-organ dysfunction (renal failure, liver injury, coagulopathy, rhabdomyolysis)

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5. Diagnosis

• Clinical: Based on history of heat exposure and symptoms/signs

• Heatstroke confirmation: Core temperature ≥40 °C plus CNS dysfunction

• Labs (especially in suspected heatstroke):

  • CBC, electrolytes, renal and liver function

  • Coagulation profile

  • Creatine kinase (for rhabdomyolysis)

  • Arterial blood gas

  • Urinalysis (myoglobinuria)

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6. Management

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Heat Exhaustion

Goals: Cool the patient, restore fluids and electrolytes, prevent progression to heatstroke.

1. Move to a cool, shaded, or air-conditioned environment

2. Position: Lie down with legs elevated

3. Remove excess clothing

4. Active cooling: Cool wet cloths, fans, ice packs to groin/axilla/neck

5. Rehydration:

   • Oral fluids with electrolytes if conscious and not vomiting (e.g., oral rehydration solution)

   • IV fluids (normal saline) if unable to tolerate oral intake or if hypotensive

6. Monitor: Vital signs, symptoms resolution within 30–60 minutes

7. Avoid return to strenuous activity for at least 24–48 hours after recovery

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Heatstroke – Medical Emergency

Goals: Rapid reduction of core temperature to <39 °C within 30 minutes, support vital functions, prevent complications.

1. Activate emergency services immediately

2. Airway, Breathing, Circulation (ABCs) – Secure airway if unconscious, give high-flow oxygen

3. Rapid cooling:

   • Evaporative cooling: Spray lukewarm water + fans to enhance evaporation

   • Ice-water immersion (most effective for exertional heatstroke if feasible)

   • Ice packs to neck, axillae, groin

   • Cooling blankets or cold IV saline lavage in severe cases

4. Remove restrictive clothing

5. IV fluid resuscitation: Normal saline to correct hypotension and dehydration; avoid overhydration

6. Treat seizures: Benzodiazepines (e.g., diazepam 5–10 mg IV) if needed

7. Monitor and treat complications:

   • Rhabdomyolysis → aggressive hydration, monitor urine output

   • Electrolyte abnormalities (hyper/hyponatremia, hyperkalemia) → correct accordingly

   • Coagulopathy/DIC → supportive hematologic care

   • Renal or hepatic dysfunction → supportive management in ICU

8. Avoid antipyretics (paracetamol, NSAIDs) – ineffective and may cause harm

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7. Prevention

• Gradual acclimatization to hot environments

• Adequate hydration before, during, and after physical activity

• Wear light, loose, breathable clothing

• Avoid strenuous activity in peak heat hours

• Ensure shaded rest breaks during outdoor work

• For high-risk individuals (elderly, chronic illness), monitor during heat waves

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8. Prognosis

• Heat exhaustion: Excellent with prompt treatment; full recovery expected

• Heatstroke: Mortality 10–30% even with treatment; survivors risk long-term neurological or organ impairment if cooling is delayed