Acute mountain sickness


  • Also referred to as AMS
  • Usually only occurs with altitude >7,000-8,000ft
    • May occur at lower altitudes in patients who are particularly susceptible (COPD, CHF)
  • Development of symptoms based on: rate of ascent, sleeping altitude, strength of hypoxic ventilatory response, alcohol intake, obesity
    • NOT based on physical fitness, age, sex, smoking, previous high-altitude experience
  • Tend to have recurrence of symptoms whenever they return to the symptomatic altitude

Clinical Features


  • Symptoms usually develop 1-6hr after arrival at elevation
    • May be delayed for 1-2d
  • Especially common after the 1st or 2nd night's sleep


  • Average duration of symptoms at 10,000ft = 15hr
  • At higher elevations symptoms may last weeks / more likely to progress to headache

Differential Diagnosis

High Altitude Illnesses


  • Clinical diagnosis
  • Mental status, cerebellar exam
  • Lung exam - rule out HAPE


High altitude management algorithm.


  • Terminate ascent and/or descend [2]
    • Descend to lower altitude (by 1000-3000ft) OR acclimatize for 12-36hr at same altitude
  • Acetazolamide
    • Mechanism: speeds acclimatization by promoting bicarb diuresis
    • Indications:
      • History of altitude illness
    • Abrupt ascent to >9800ft
      • AMS requiring treatment
      • Bothersome periodic breathing during sleep
    • 125-250mg PO BID until symptoms resolve
    • Side-effects
      • Allergic reaction (if patient allergic to sulfa), paresthesias, polyuria, carbonated beverages taste bitter
  • Symptomatic treatment as necessary with analgesics and antiemetics
  • Sleep-agents


  • Immediate descent for worsening symptoms
  • Low-flow 0.5-1 L/min O2 if available (especially nocturnal administration)
  • Acetazolamide 250mg PO BID
  • Dexamethasone 4mg PO q6hr
    • Symptom-improvement only; unlike acetazolamide does not aid acclimatization
  • Hyperbaric therapy


  • Graded ascent with adequate time for acclimatization is the best prevention
  • Acetazolamide prophylaxis
    • Indicated for patients with history of altitude illness or forced rapid ascent to altitude
    • Start 24hr before ascent and continue for the first 48hrs at peak altitude
    • Can be restarted if illness develops
    • Reduces symptoms of AMS by 75% in patients ascending rapidly to altitudes >8200ft
  • Dexamethasone[3]
    • Start day of ascent and continue for first 2 days at altitude
    • 4mg PO q12hr
    • Prevents and treats cerebral edema
  • Ginkgo biloba
    • Controversial if effective; safe
  • Ibuprofen
    • Prevention - less effective than acetazolamide, better than placebo
    • Treatment of headache (however, important to consider that taking ibuprofen may mask symptoms)


See Also


  1. Schneider M et al. Acute mountain sickness: Influence of susceptibility, preexposure, and ascent rate. Med Sci Sports Exerc 2002; 34:1886-1891.
  2. Luks A, McIntosh S, Grissom C, Auerbach P, Rodway G, Schoene R, Zafren K, Hackett P. Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2014 Update. Wilderness Environ Med. 2014; S4-S14.
  3. Luks AM, McIntosh SE, Grissom CK, et al. Wilderness Medical Society Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness: 2014 Update. Wilderness & Environmental Medicine. 2014(25): S4–S14)