Key takeaways
- HACE is a life-threatening swelling of the brain from fluid accumulation at high altitude.
- Defining signs: confusion, loss of coordination (ataxia), and altered behavior or consciousness.
- It's often the severe end stage of acute mountain sickness (AMS).
- Treat with immediate descent (plus oxygen and dexamethasone if available) — it can be fatal in hours.
Acronym: High-Altitude Cerebral Edema.
This is general educational information, not medical advice. HACE is a medical emergency — descend immediately and seek professional help.
What HACE is
HACE — high-altitude cerebral edema — is a swelling of the brain caused by fluid buildup at high altitude, and the most severe form of altitude illness. It’s often the end stage of untreated acute mountain sickness (AMS): what begins as a bad altitude headache can progress to this life-threatening brain emergency, fatal within hours if ignored.
Warning signs
- Loss of coordination (ataxia) — the classic sign; the person can’t walk a straight heel-to-toe line.
- Confusion and irrational or altered behavior.
- Severe headache, nausea, drowsiness, sometimes hallucinations.
- Progression to unconsciousness.
A trekker becomes uncharacteristically confused and stumbles as if drunk, failing the heel-to-toe walking test. The group treats it as HACE, gives dexamethasone if available, and descends with them immediately — never letting them go down alone.
Treatment and prevention
Immediate descent is the lifesaving treatment; dexamethasone, oxygen, and a hyperbaric chamber can buy time but don’t replace it. Prevent it by ascending gradually, acclimatizing, and acting on early AMS. The lung counterpart is HAPE — see HAPE vs HACE.
The bottom line
HACE is brain swelling at altitude — the deadliest altitude illness, marked by confusion and stumbling coordination. Recognize ataxia and altered mental state as emergencies, and respond the same way as for HAPE: descend immediately, assisted, with oxygen and dexamethasone if available. Gradual ascent and heeding early AMS symptoms prevent it from ever reaching this stage.
Frequently asked questions
What is HACE?
HACE, or high-altitude cerebral edema, is a swelling of the brain caused by fluid buildup at high altitude. It's the most severe form of altitude illness, frequently the progression of untreated acute mountain sickness, and it is a life-threatening emergency that can be fatal within hours without descent.
What are the symptoms of HACE?
The hallmark signs are neurological: confusion, irrational or altered behavior, and a loss of coordination called ataxia (a classic test is the inability to walk a straight heel-to-toe line). Severe headache, nausea, drowsiness, hallucinations, and progressing to unconsciousness also occur. Ataxia and confusion at altitude are HACE until proven otherwise.
How is HACE treated?
Immediate descent is the definitive, lifesaving treatment. The steroid dexamethasone and supplemental oxygen, plus a portable hyperbaric chamber, can help buy time during evacuation, but they don't substitute for going down. Do not let someone with suspected HACE continue ascending or descend alone — they need assistance.
Sources
- High-altitude illness — Wilderness Medical Society
- Altitude illness — CDC
- Mountain medicine — UIAA