High Altitude Cerebral Edema (HACE)

1. Definition

High-Altitude Cerebral Edema (HACE) is a life-threatening form of acute high-altitude illness, characterized by:

• Severe neurologic dysfunction
• Ataxia (early sign)
• Altered sensorium progressing to coma
• Occurs typically at >2,500–3,000 m, but more common above 4,000 m

HACE represents the severe end of the Acute Mountain Sickness (AMS) spectrum.

2. Epidemiology

• Usually develops after rapid ascent
• Typically occurs 2–5 days after arrival
• Rare below 3,000 m
• Risk increases with:
• Rapid ascent
• Previous HACE
• Young age
• Heavy exertion
• Dehydration
• Concomitant High-Altitude Pulmonary Edema (HAPE)

3. Pathophysiology 

Hypoxia → Cerebral Edema

High altitude → ↓ Barometric pressure → ↓ Inspired PO₂ → Hypoxemia → Cerebral consequences:

A. Vasogenic Edema (Primary mechanism)

• Hypoxia → cerebral vasodilation
• ↑ Capillary hydrostatic pressure
• Blood–brain barrier (BBB) disruption
• Extravasation of plasma proteins → white matter edema

Predominantly affects:

• Corpus callosum (especially splenium)
• Subcortical white matter

B. Cytotoxic Edema (Secondary mechanism)

• Cellular hypoxia
• Failure of Na⁺/K⁺ ATPase
• Intracellular swelling

C. Increased ICP

• Edema → ↑ ICP → ↓ CPP → worsening hypoxia
• Brainstem compression → coma, death

4. Relationship to AMS and HAPE

HACE is essentially AMS + ataxia and/or altered mental status.

5. Clinical Features

Early

• Severe headache
• Fatigue
• Irritability
• Nausea/vomiting
• Poor concentration

Progressive (Diagnostic)

• Ataxia (most sensitive sign)
• Confusion
• Dysarthria
• Hallucinations

Late

• Drowsiness
• Stupor
• Coma
• Seizures (rare)
• Papilledema (inconsistent)

6. Diagnosis

Clinical Diagnosis (No delay for imaging)

Diagnosis =Recent altitude exposure +Severe AMS +Ataxia and/or altered mental status

Lake Louise Score (LLS)

Used for AMS; not specific for HACE but supportive.

7. Differential Diagnosis 

8. Imaging

CT Brain

Often normal or mild edema.

MRI Brain (More sensitive)

Typical findings:

• T2/FLAIR hyperintensity
• Splenium of corpus callosum involvement
• White matter edema
• Microhemorrhages (in severe cases)

9. Management 

 This is a MEDICAL EMERGENCY

1️⃣ Immediate Descent (Definitive Treatment)

• Descend at least 500–1,000 m
• Most effective intervention
• Mortality decreases dramatically

2️⃣ Oxygen Therapy

• Target SpO₂ > 90%
• High-flow oxygen preferred
• Mechanical ventilation if comatose

3️⃣ Dexamethasone (Drug of Choice)

• Reduces vasogenic edema
• Stabilizes BBB

 Does NOT replace descent.

4️⃣ Portable Hyperbaric Chamber (Gamow Bag)

Used when descent not possible.

Mechanism:

• Simulates descent
• Temporary measure

5️⃣ ICU Management

If coma or severe case:

• Airway protection
• Mechanical ventilation
• Head elevation 30°
• Maintain CPP
• Avoid hypotension
• Control seizures (if present)

6️⃣ Role of Mannitol?

 Not routinely recommended
May worsen dehydration
Limited evidence

10. Prognosis

• Rapid improvement within 24–48 hrs if treated early
• Mortality high if untreated
• Full recovery possible
• Delayed descent → brain herniation → death

11. Prevention 

Gradual Ascent Rule

• < 300–500 m sleeping elevation per day above 3,000 m
• Rest day every 3–4 days

Acetazolamide (Prophylaxis)

• Carbonic anhydrase inhibitor
• Causes metabolic acidosis → ↑ ventilation

Dexamethasone

• Used in high-risk individuals
• Not preferred for routine prophylaxis

12. HACE vs HAPE – Rapid Comparison

13. Complications

• Brain herniation
• Persistent cognitive deficits
• Death