High-Altitude Illness: AMS, HAPE, and HACE

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Updated July 2026  |  More ICU nursing guides →

High-altitude illness is what happens when the body ascends faster than it can acclimatize to falling oxygen. Most nurses will not see it in a coastal ICU, but mountain-region hospitals, flight and transport teams, and any unit near ski country encounter it — and its two severe forms, high-altitude pulmonary edema (HAPE) and high-altitude cerebral edema (HACE), are true emergencies. The organizing idea is simple: these illnesses live on a spectrum, they are driven by hypoxia, and the definitive treatment for the dangerous end of that spectrum is descent.

The spectrum, from nuisance to fatal

Acute mountain sickness (AMS) is the common, mild end: headache plus some combination of nausea, fatigue, dizziness, and poor sleep, appearing hours after arriving at altitude. It usually resolves with rest and stopping further ascent. The danger is that AMS can progress. HACE is essentially the brain-swelling end of the same process — AMS plus neurologic signs, most classically ataxia (a stumbling, can't-walk-a-straight-line gait) and altered mental status. HAPE is a separate but overlapping process in the lungs: hypoxic pulmonary vasoconstriction drives fluid into the alveoli, producing dyspnea, cough, and hypoxemia that is out of proportion to anything else. HAPE and HACE can occur together, and both can kill.

Why descent is the treatment

Every other intervention buys time; descent fixes the cause. Even a modest loss of altitude often produces dramatic improvement in HAPE and HACE, and delay is what turns these into fatalities. In the hospital setting the patient has already "descended" to sea-level pressure or is on supplemental oxygen, so the nursing focus shifts to oxygenation and monitoring — but the mental model of "the answer is lower altitude / more oxygen" explains why everything else is adjunctive. A portable hyperbaric (Gamow) bag simulates descent in the field when real descent is impossible.

The drugs, and what each one is for

The pharmacology of altitude illness confuses people because three different drugs get mentioned. Keeping their jobs separate is the whole point:

Acetazolamide is a carbonic anhydrase inhibitor that produces a mild metabolic acidosis, which stimulates breathing and helps the body acclimatize; it is the classic AMS prevention drug and causes a harmless tingling and a flat taste to carbonated drinks that patients often notice. Dexamethasone treats the brain swelling of HACE but does not speed acclimatization the way acetazolamide does. Nifedipine relieves the hypoxic pulmonary vasoconstriction that drives HAPE. Phosphodiesterase inhibitors are sometimes used for HAPE as well. The nurse's role is knowing which drug maps to which problem so the orders make sense at the bedside.

Nursing priorities in the unit

For the HAPE patient, the priorities look like any hypoxemic respiratory patient: titrate oxygen to a target saturation, position upright, minimize exertion (which worsens the hypoxic pulmonary pressures), and escalate to non-invasive or invasive support if oxygenation fails — the same lung-protective principles covered in lung-protective ventilation apply if intubation becomes necessary. For the HACE patient, the priorities are neurologic: frequent neuro checks, protect the airway as consciousness declines, and watch the gait and mental status as your earliest trend. In both, oxygen is continuous and the team is arranging the "descent" the patient can't do for themselves.

For the respiratory support side, see lung-protective ventilation for ARDS and PEEP titration; for the neuro monitoring, neuro checks and the Glasgow Coma Scale. Related environmental emergencies: decompression sickness.