High‑altitude cerebral oedema (HACE / HACO)
Overview
High‑altitude cerebral oedema (HACE) is the most severe form of altitude illness-an acute, potentially fatal encephalopathy caused by cerebral oedema after ascent to high altitude. It typically develops 2-4 days after ascent and commonly follows moderate-severe acute mountain sickness (AMS).
Rapid recognition and immediate treatment (descent, oxygen, steroids) are essential. Untreated HACE can progress to coma, brain herniation and death within 24 hours.
Pathophysiology (concise) Sustained hypoxaemia at altitude leads primarily to vasogenic cerebral oedema:
- Cerebral vasodilatation with increased cerebral blood flow and vascular pressure.
- Endothelial dysfunction with increased blood-brain barrier permeability.
- Extravasation of plasma into the interstitium (predominantly white matter), increasing intracranial pressure (ICP) and impairing cerebral perfusion.
Cytotoxic mechanisms may contribute, but the dominant process is leakage across a disrupted blood-brain barrier.
Epidemiology and timing
- Incidence is lower than high‑altitude pulmonary oedema (HAPE); approximately 1-2% in people who ascend rapidly to around 4 500 m.
- Typical onset is 2-4 days after ascent.
- Often occurs in association with moderate-severe AMS.
- Progression can be rapid; prompt descent markedly improves outcome.