Skip to Main Content



  • Altitude illness is likely to occur at >2500 m and has occurred even at 1500–2500 m.

  • 100 million persons travel to high-altitude locations each year.


Acute Mountain Sickness (AMS), Including HACE

AMS represents a clinical continuum of neurologic disease, of which high-altitude cerebral edema (HACE) is the most severe form.

  • Risk factors: rate of ascent, history of high-altitude illness, exertion

    • – Lack of physical fitness is not a risk factor.

    • – Exposure to high altitude within the preceding 2 months may be protective.

    • – Pts >50 years old may be less likely to develop AMS than younger pts.

  • Pathophysiology: Although the exact mechanisms remain unknown, hypoxic cerebral vasodilatation and altered permeability of the blood-brain barrier contribute to cerebral edema in AMS.

  • Clinical manifestations

    • – Nonspecific symptoms (headache, nausea, fatigue, and dizziness) with a paucity of physical findings, developing 6–12 h after ascent to a high altitude

    • – HACE: encephalopathy whose hallmarks are ataxia and altered consciousness with diffuse cerebral involvement but generally without focal neurologic deficits

      • Retinal hemorrhages and, less commonly, papilledema may be seen.

      • Retinal hemorrhages occur frequently at ≥5000 m irrespective of the presence of symptoms of AMS or HACE.

  • Prevention: Gradual ascent with acclimation is the best measure to prevent AMS.

    • – At >3000 m, a graded ascent of ≤300 m each day is recommended.

    • – Taking an extra day for acclimation after 3 days of gain in sleeping altitude is helpful.

    • – Pharmacologic prophylaxis is warranted when the pt has a history of AMS or when flight to a high-altitude location is required.

      • Acetazolamide (125–250 mg PO bid) or dexamethasone (8 mg/d in divided doses), administered 1 day before ascent and continued for 2–3 days, is effective.

      • Gingko biloba is ineffective for prevention of AMS.

TREATMENT Acute Mountain Sickness

See Table 31-1.


Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.