Approximately 20% of people will develop mild symptoms at altitudes between 6,300 to 9,700 feet, but pulmonary and cerebral edema are extremely rare at these heights. However, above 14,000 feet, a majority of people will experience at least mild symptoms. Some people who stay at this height can develop pulmonary or cerebral edema.
Symptoms generally associated with mild to moderate altitude illness include:
Dizziness or light-headedness
Loss of appetite
Nausea or vomiting
Rapid pulse (heart rate)
Shortness of breath with exertion
Symptoms generally associated with more severe altitude illness include:
Bluish discoloration of the skin
Chest tightness or congestion
Coughing up blood
Decreased consciousness or withdrawal from social interaction
Gray or pale complexion (cerebral edema)
Inability to walk in a straight line, or to walk at all
Shortness of breath at rest
- If possible, you should spend at least one night at an intermediate elevation below 3000 meters (10,000 feet).
- At altitudes above 3000 meters (10,000 feet), your sleeping elevation should not increase more than 300-500 meters (1000-1500 feet) per night.
- Every 1000 meters (3000 feet) you should spend a second night at the same elevation.
Remember, it's how high you sleep each night that really counts; climbers have understood this for years, and have a maxim "climb high, sleep low". The day hikes to higher elevations that you take on your "rest days" (when you spend a second night at the same altitude) help your acclimatization by exposing you to higher elevations, then you return to a lower (safer) elevation to sleep. This second night also ensures that you are fully acclimatized and ready for further ascent.
Respiratory depression (the slowing down of breathing) can be caused by various medications, and may be a problem at altitude. The following medications can do this, and should never be used by someone who has symptoms of altitude illness (these may be safe in persons who are not ill, although this remains controversial):
- Sleeping pills