Medical / Travel

Facts About Altitude Sickness: Acute Mountain Sickness, High Altitude Cerebral Edema, High Altitude Pulmonary Edema

Acute mountain sickness (AMS), high altitude cerebral edema (HACE), and high altitude pulmonary edema (HAPE) represent a progression of the same disorder.

The higher the altitude, the lower the atmospheric pressure. The oxygen level stays the same but the partial pressure of oxygen decreases. This causes changes to the cells of the brain and lung primarily.

The mildest form of altitude sickness is acute mountain sickness. This can occur at altitudes as low as 6500 ft. The highest mountain in the Appalachians is North Carolina’s Mt. Mitchell at 6684 ft.; Yosemite’s Half Dome is 8835 ft. high. Skiers and hikers are particularly at risk.

Acute Mountain Sickness (AMS)

Symptoms: Basically like those of a hangover.

  • Headache and at least one of the following;
  • Fatigue
  • Nausea, vomiting, or decreased appetite
  • Dizziness
  • Sleep disorder (either too much or too little)
  • Increased activity makes worse

High Altitude Cerebral Edema (HACE)

This is a progression of acute mountain sickness.

Symptoms are due to swelling of the brain (cerebral edema) and are;

  • Headache
  • Confusion
  • Staggering (ataxia) as if drunk.
  • Seizures
  • Weakness or damage to nerves that control the eyes, facial, tongue, and swallowing movement (cranial nerve palsy)
  • Damage to visual nerves and retina
  • Progresses to stupor, comatose state, and death, if untreated, often as rapidly as a few hours.

High Altitude Pulmonary Edema (HAPE)

Symptoms usually develop within 1-4 days of a rapid ascent to over 8000 ft. (Mount Olympus, Washington 7979 ft., El Capitan, Texas 8084 ft., Mount St. Helens, Washington 8366 ft.) This is the #1 cause of climber’s deaths. Symptoms are:

  • Shortness of breath
  • Inability to tolerate much activity
  • Rapid breathing and heart rate
  • Cough- often with pink or bloody sputum
  • Untreated, death can occur in hours

Treatment: This is pretty straight forward in the field and consists of:

  • For mild AMS, halt the accent and acclimate. See prevention.
  • Increase fluid intake
  • Acetazolamide (Diamox) a diuretic, 250mg twice a day or 500 mg of extended release, by mouth, once a day
  • HAPE and HACE: Descend immediately if possible
  • O² and portable hyperbaric bag
  • For HAPE, nifedipine 10mg by mouth may help initially
  • With descent, symptoms usually resolve in 24-48 hrs.


  • The two most important things are acclimatizing with a slow ascent and starting to get well hydrated prior to the ascent
  • The recommended ascent rate from 8000 ft. is sleeping the first 2-3 nights at 8000-10,000 ft. followed by sleeping another night per every additional 1000 ft. of climbing e.g. overnight at 11,000 ft. then 12,000 ft. and so forth
  • These times may be pushed forward if a quick ascent and return are planned


  • Physical fitness has nothing to do with this condition just as it has little to do with motion sickness. This isn’t to say that medical conditions such as heart disease aren’t a factor.
  • Alcohol can worsen symptoms
  • If traveling in a group, the pace of ascent needs to be that of the slowest member of the group.
  • If a person has any one of the conditions altitude sickness conditions, they are at higher risk of a recurrence and they need to notify their partners ahead of time.
  • No one can acclimate completely to altitudes over 17,000 ft. Everest is 29,029 ft.; Denali in Alaska is 20,236 ft.
  • If there is a respiratory infection (cold, cough, etc.) prior to or during an accent, it can accelerate and worsen symptoms.
  • Aircraft cabin pressure at 39,000 ft. is typically maintained at a pressure equal to 4500 to 7500 ft.
  • Divers have a “No Fly” period. After prolonged diving, nitrogen builds in the body from the higher, below sea level pressures. They are subject to decompression sickness, even at altitudes less than 8000 ft.


  • See terms and conditions
  • Some of the information for this post comes from the Merck Manual, 19th edition.

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