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High-altitude travel: Altitude sickness

High-altitude travel can occasionally lead to health problems such as altitude sickness, which is also known as mountain sickness. The health issues observed are the result of inadequate acclimatization to the lack of oxygen at higher elevations and become more noticeable above 2,500 meters (even 2,000 meters for some). Altitude sickness includes a number of medical problems such as:

  • Acute mountain sickness (AMS) - AMS is quite common and symptoms resemble those of a hangover.
  • High-altitude cerebral edema (HACE) - HACE, a rare and potentially life-threatening illness, is a severe presentation of AMS. It is characterized by loss of coordination, unusual behaviour, extreme fatigue, sleepiness and loss of consciousness due to swelling of the brain.
  • High-altitude pulmonary edema (HAPE) - HAPE, which is quite uncommon and potentially life-threatening, is caused by an accumulation of fluid in the lungs. Symptoms include: breathlessness at rest or with exertion, rapid heart rate, a dry, throaty cough, coloured secretions (pinkish to blood red) and respiratory distress.


Travel to high elevations may aggravate underlying illnesses, and may even bring to light other illnesses such as heart and respiratory diseases.

There is no link between physical fitness and susceptibility to altitude sickness. Certain factors however, do increase one's risk of developing altitude sickness:

  • A past history of altitude sickness
  • Strenuous activity, consumption of alcohol or sedatives prior to acclimatizing
  • A rapid ascent

Regardless of your fitness level, it is important to speak to your healthcare provider before leaving to take a closer look at the overall state of your health, your travel plans (altitude of your stay, rate of ascent), the availability of medical care along the intended route of travel and the possible need for medication to prevent and/or treat altitude sickness.

Acute mountain sickness (AMS)

AMS is the most common form of altitude sickness. It affects close to 25% of adults sleeping above 2,400 meters and approximately 40 to 50% of those sleeping above 3,000 meters. Symptoms usually occur 6 to 24 hours after arrival at a higher altitude and can last 2 to 5 days after ascent is stopped. Symptoms associated with AMS include:

  • Headache
  • Nausea that is sometimes accompanied by vomiting
  • Loss of appetite
  • Breathlessness
  • General fatigue
  • Dizziness
  • Insomnia and other sleep disorders

Preventing AMS

Gradual ascent is the safest and most efficient way to prevent AMS. In other words, the key is to follow the golden rule used by climbers: «Climb high, Sleep low». In fact, acclimatization is easier if you spend the night at an altitude that is lower by a few hundred meters than the highest point reached during the day.

The following preventive measures are recommended to aid acclimatization:

  • Avoid strenuous activities and alcohol during the acclimatization period, particularly during the first 48 hours
  • Avoid fast ascent to sleeping altitudes beyond 3,000 meters
  • Spend 2 to 3 nights at 2,500 to 3,000 meters before going higher
  • Avoid ascending more than 300 to 400 meters a day beyond 3,000 meters
  • If continuing ascent, spend an extra night for acclimatization every 600 to 900 meters
  • Beyond 3,000 meters, avoid alcohol and medications that have an effect on breathing (i.e.: sleeping pills, anti-anxiety medications and certain pain medications)
  • Plan a rest day with 2 nights at the same altitude, every 3 to 4 days
  • Hydrate and opt for carbohydrate-rich foods
  • Avoid overexertion and opt for moderate activities
  • Avoid smoking

It is particularly significant for those who have suffered from altitude sickness in the past or who are planning a rapid ascent, to take medication as a preventive measure against AMS.

Treating AMS

As soon as you feel the first symptoms of AMS, stop climbing. Ignoring the initial symptoms can lead to severe complications, including neurological deterioration or respiratory failure. It is important to rest and acclimatize at the same altitude; acclimatization may take 12 hours to 4 days. If symptoms persist or progress, descend immediately to an altitude at least 500 meters lower than where the symptoms began. It is important to promptly seek medical help if symptoms worsen or do not disappear.

Some symptoms are similar to those of AMS but are in fact the result of intense exertion, ascent-related stress, dehydration, etc. The Lake Louise scale may help assess symptoms.

If you have symptoms that resemble those of high-altitude cerebral edema or high-altitude pulmonary edema, descend immediately by 500 meters or more and seek medical advice. Delaying the descent will increase the risk of potentially life-threatening complications.

Before your leave, speak to your healthcare provider as he or she may prescribe a product that prevents or accelerates acclimatization. An analgesic such as acetaminophen (i.e.: Tylenol®) or ibuprofen (i.e.: Motrin®, Advil®) may also be recommended to relieve AMS-related headache.

For more information:

Public Health Agency of Canada

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