Mountain Sickness

Frank Gillingham, MD

Modern travel has made it easy to reach high altitude destinations such as the Peruvian Andes, Lhasa (Tibet), or even the ski resorts of Colorado, without doing any actual mountain climbing. If you're planning such a trip, be sure to familiarize yourself with the health effects of altitude.


First, some basics. Because of the effect of gravity on the atmosphere, air pressure falls as you ascend above sea level. Though the percentage of oxygen in air remains about the same (21%), the air is 'thinner.' The result is a decline in the absolute amount of oxygen available, which results in a decline in the amount of oxygen available to your tissues. Without sufficient oxygen, your tissues can't convert nutrients into energy.

At sufficiently high altitudes (above 8000 ft., typically), symptoms can occur in anyone. Oddly enough, physical conditioning does not seem to protect against Mountain Sickness. In fact, it often strikes younger, more fit members of climbing expeditions and is less common in those over 50. Tolerance to high altitude varies tremendously between individuals, and can vary from trip to trip for the same individual. Cold weather seems to worsen the effects of altitude.

Anyone with chronic medical conditions or a history of lung or heart problems should discuss travel to a high altitude destination with a physician well in advance of travel. Individuals who suffer from the following chronic medical conditions should never travel to high altitude destinations:

Those who suffer from asthma or coronary artery disease are also at increased risk, and should be certain to have a thorough evaluation by a physician prior to travel.

Everyone who visits a high altitude destination will breathe more frequently and experience increased heart rate and pulse. Dryness of the skin and mucous membranes occurs, as does minor headache. These are normal mechanisms of high altitude adaptation.

Acute Mountain Sickness

Acute Mountain Sickness (AMS) is more common in those who have ascended too rapidly above 2,400 meters (8,000) feet. Typical symptoms include:

The symptoms typically develop within 36 hours at altitude.

The most severe forms of AMS are "High Altitude Cerebral Edema" (HACE), which is result of swelling of the brain from fluid leakage, and "High Altitude Pulmonary Edema" (HAPE) which results from fluid build-up in the lungs. Trekkers suffering from HACE are unable to walk a straight line, become disoriented, and can lapse into a coma if not given proper medical treatment. Signs of HAPE that can be detected by medical personnel or laboratory testing include widespread wet noises (crackles) in lungs, and extremely low oxygen levels. Left untreated, HAPE can lead to death in the most severe cases.


Proper acclimatization, the process of allowing the body time to adapt to the decrease in oxygen molecules, may help prevent AMS. Gradual ascent is crucial.

Treatment of AMS

Buddya Basnyat, M.B.B.S., a Participating Physician in Kathmandu, Nepal, wrote in the September 1999 issue of the Journal of Travel Medicine that despite an increase in trekkers entering the Himalayas in Nepal, the number of cases of severe AMS cases has not increased. Dr. Basnyat attributes the decease in the rate of AMS to the success of education campaigns by organizations such as the Himalayan Rescue Association, among others.

Special thanks to Carol Foley, Dr. Gustavo Zubieta-Calleja, Sr. (LaPaz, Bolivia, Dr. Buddya Basnyat (Kathmandu, Nepal) and Dr. Matthew Rusk (Philadelphia, PA, USA) for assistance in preparing this article.