High-Altitude Cerebral Edema (HACE): Symptoms, Causes & Prevention

HACE is a life-threatening encephalopathy from hypobaric hypoxia at altitude. It is the end-stage of acute mountain sickness (AMS).

Pathophysiology

• Hypoxia → cerebral vasodilation → increased cerebral blood flow → capillary leakage → vasogenic edema
• Impaired autoregulation, inflammatory mediators (VEGF, MMPs), free radicals
• Typically >3000m (9800 ft), but reported at 2500m (8200 ft)
• Incidence: 0.5–1% at 4000m; higher with rapid ascent

Clinical Presentation (Often Follows AMS)

• AMS prodrome: Headache, nausea, fatigue, insomnia
• HACE hallmarks:
  • Altered mental status: confusion, apathy, ataxia (truncal > appendicular)
  • Gait ataxia (heel-to-toe test) — most sensitive sign
  • Papilledema (late)
  • Cranial nerve palsies (rare)
  • Seizures, coma (terminal)

Diagnosis

• Clinical (Lake Louise Score ≥3 + ataxia/altered mental status)
• MRI: T2/FLAIR hyperintensities in corpus callosum, white matter (reversible)
• Rule out: stroke, tumor, meningitis, metabolic

Immediate Treatment (Life-Saving)

1. DESCEND IMMEDIATELY: ≥500–1000m (1500–3000 ft). Do not wait for helicopter if walking possible.
2. Supplemental O₂: Target SpO₂ >90%. Portable hyperbaric chamber (Gamow bag) if descent delayed.
3. Dexamethasone: 8 mg PO/IV/IM stat, then 4 mg q6h. Reduces edema. Continue until descent + 24h asymptomatic.
4. Acetazolamide: 250 mg q12h (adjunct — aids acclimatization)
5. Monitor: GCS, vitals, fundoscopy if possible

Prevention

• Graded ascent: ≤300–500m (1000–1600 ft) gain/day above 3000m. Rest day every 3–4 days / 1000m.
• Acetazolamide prophylaxis: 125 mg q12h starting 24h before ascent (if rapid ascent unavoidable)
• Hydration, nutrition, avoid alcohol/sedatives
• Pre-acclimatization: Hypoxic tents, prior high-altitude exposure
• Recognize AMS early — treat/descend before HACE develops

HACE is a medical emergency. Descent + dexamethasone + oxygen = survival. Never ascend with symptoms.