Hyperthermia: Progressive Symptoms from Heat Stress to Life-Threatening Emergency

Hyperthermia (core temperature >38.5°C/101.3°F from failed thermoregulation) progresses through predictable stages. Early recognition saves lives.

Stage 1: Heat Stress / Exhaustion (Core 38.5–40°C)

• Profuse sweating → dehydration, electrolyte loss
• Tachycardia, tachypnea
• Muscle cramps (heat cramps)
• Fatigue, weakness, dizziness
• Headache, nausea
• Orthostatic hypotension

Stage 2: Heat Injury (Core 40–40.5°C)

• CNS dysfunction: confusion, irritability, ataxia
• Vomiting, diarrhea
• Hypotension, oliguria
• Creatinine kinase rise (rhabdomyolysis risk)

Stage 3: Heat Stroke (Core >40.5°C) — MEDICAL EMERGENCY

• Classic (non-exertional): Elderly, chronic illness, meds (anticholinergics, diuretics, beta-blockers)
• Exertional: Athletes, laborers, military in heat
• Hallmarks: Anhidrosis (late), altered mental status (delirium, coma, seizures), multi-organ failure (coagulopathy, hepatic/renal failure, ARDS)
• Mortality: 10–50% even with treatment; higher with delay

Immediate First Aid

1. Call EMS.
2. Move to shade/AC.
3. Rapid cooling: ice-water immersion (gold standard), evaporative (mist + fan), ice packs to neck/axillae/groin.
4. IV fluids if available.
5. Monitor core temp (rectal/esophageal).

Prevention

• Hydrate pre/during/after activity
• Acclimatize 7–14 days
• Light, loose clothing
• Schedule activity in cooler hours
• Know medication heat risks