Definition: 3 distinct clinical entities caused by acute hypoxia at elevation. Usually occurs at >2500 meters above sea level.

  • At altitudes greater than 2440 meters, the decrease in partial pressure of ambient air and thus the alveoli will result in a decrease in the oxygen saturation in healthy people (Hacket 2011)

Acute Mountain Sickness Visual (

Acute Mountain Sickness (AMS)

  • Definition: Constellation of symptoms including headache with some combination of anorexia, nausea, nausea, dizziness, sleep disturbances, malaise caused by hypoxia at altitudes >2500 meters above sea level
  • Epidemiology
    • 10-25% of all unacclimated persons at 2500m or higher (Bartsch 2013)
    • Increases 50-85% of people at 4500-5500 meters
    • Can occur at lower altitudes in persons with cardiopulmonary disease
  • Presentation
    • Headache with some combination of anorexia, nausea, nausea, dizziness, sleep disturbances, malaise
    • Onset usually 6-12 hours at >2500 meters
  • Risk factors:
    • Previous acute mountain sickness
    • Fast ascent (>625 meters per day above 2000 meters)
    • Sleeping at altitude
  • Course: usually resolves in 1-2 days if person maintains elevation but can last longer
  • Lake Louise Acute Mountain Sickness Questioner tool indicates disease severity
  • Treatment
    • Stop Ascent
    • Descend immediately: altered mental status, ataxia or pulmonary edema are noted
    • Descend if symptoms worsen or do not resolve in 1-2 days
    • Supportive care
      • Hydration
      • NSAIDs for headaches
      • Antiemetics for nausea/vomiting
  • Medications
    • Dexamethasone 4mg q6h for moderate to severe symptoms
    • Consider acetazolamide 125mg BID (Luks 2014)

High-altitude cerebral edema (HACE)

  • Clinical progression of acute mountain sickness
  • Includes cerebral hypoxia causing increased cerebral blood flow leading to potentially life-threatening cerebral vasogenic edema with microhemorrhages
  • Presentation
    • Commonly occurs 2-4 days after arriving to altitudes >2500 meters
    • Headache, nausea and vomiting are common but not obligatory
    • Continuum from truncal ataxia, altered mental status, low-grade fever, coma, herniation to death
  • Treatment
    • Priority #1: Immediate Descent
    • Supplemental O2 as needed
    • Medications
      • Dexamethasone 8mg once, then 4mg q6h until resolution of symptoms
      • Consider acetazolamide 125mg BID (Luks 2014)
  • Always consider alternative diagnosis, i.e. infections, strokes, subarachnoid hemorrhage

HAPE (Mayo Clinic)

High-altitude pulmonary edema (HAPE)

  • Non-cardiogenic, hydrostatic pulmonary edema cause by hypoxic-induced vasoconstriction leading to high microvascular pressures (i.e. altitude-dependent pulmonary hypertension)]
  • 50% fatal if untreated
  • Presentation
    • Initial symptoms: dry cough, decreased exercise tolerance, dyspnea on exertion and increased recovery time
    • Progresses to tachycardia, tachypnea, dyspnea at rest, weakness, productive cough, cyanosis, generalized rales; late findings include hypoxia, altered mental status, coma, death
    • Low resting O2 saturation for given altitude and marked drop with exertion
    • Usually presents 2-4 days at altitude >2500 meters
    • Can occur independently of other symptoms of AMS or HACE
    • In mild HAPE, 30% of patients will not have rales at rest but can be induced with exercise
    • Diagnostics
      • EKG may show right-axis deviation
      • CXR findings vary from interstitial to localized alveolar to diffuse alveolar infiltrates depending on disease severity

HAPE (Circulation)

  • Treatment
    • Immediate descent while minimizing exertion.
    • Consider hyperbaric tents if unable to descend
    • O2 supplementation to SpO2 >90% to decrease hypoxia-induces pulmonary artery vasoconstriction
    • Keep warm as hypothermia exacerbates pulmonary arterial pressures
    • Medications
      • Nifedipinee 30mg extended-release BID reduces pulmonary artery pressures
      • Phosphodiesterase-5 inhibitors used for prophylaxis and possible treatments as shown to blunt hypoxic pulmonary vasoconstriction (Bartsch 2013)
      • Inhaled salmeterol can be used for prophylaxis
      • No known utility for steroids or diuretics

Take Home Points

  1. Headache at altitude is concerning for AMS and can progress to HACE
  2. Suspecting HAPE is the key to diagnosing HAPE. Look for inappropriate dyspnea at rest or with exertions, lower resting oxygen saturations compared with peers
  3. Descent is the most important treatment for AMS, HACE, and HAPE

Read More:

Life in the Fast Lane: High Altitude Illness


Bartsch P, Swenson E. Acute High-Altitude Illnesses. NEJM 2013;368 (24): 2294-2302. PMID: 23758234

Hacket P, Hargrove J. High-Altitude Medical Problems in Tintinalli JE, Stapczynski JS, Ma OJ, Cline DM, Cydulka RK, Meckler GD, et al (eds): Tintinalli’s Emergency Medicine: A Comprehensive Guide, ed 7. McGraw Hill Companies, Inc., 2011, (Ch) 216: p 1403-1410.

Luks A et. al. Wilderness Medical Society practice guidelines for the prevention and treatment of acute altitude illness: 2014 update. Wilderness and Environ Med 2014; 25:S4-S14. PMID: 25498261.