What is it: altitude sickness is divided into three syndromes: acute mountain sickness (AMS), high-altitude cerebral edema (HACE), and high-altitude pulmonary edema (HAPE). AMS is the most common form of altitude illness and, while it can occur at altitudes as low as 1,219–1,829 m (4,000–6,000 ft), most often it occurs in abrupt ascents to over 2,743 meters (over 9,000 ft).
How do I get it: travellers whose itineraries who find themselves at an altitude of 1,829–2,438 m (6,000–8,000 ft) and above should are exposed to the risk of altitude sickness. This could happen for example by flying into a high-altitude city, by driving to a high-altitude destination, or by hiking or climbing in high mountains. High-altitude cities with airports are Cuzco, Peru (3,000 m; 11,000 ft); La Paz, Bolivia (3,444 m; 11,300 ft); or Lhasa, Tibet (3,749 m; 12,500 ft).
What happens if I get it: symptoms often resemble an alcohol hangover: headache, fatigue, loss of appetite, nausea, and, occasionally, vomiting. The onset of the most common form, acute mountain sickness is delayed, usually beginning 6–12 hours after arrival at a higher altitude, but occasionally more than 24 hours after ascent.
Diagnosis and treatment: the three rules that travellers should be made aware of to prevent death from altitude illness are:
- Learn the early symptoms of altitude illness and be willing to admit that you have them.
- Never ascend to sleep at a higher altitude when experiencing any of the symptoms of altitude illness, no matter how minor they seem.
- Descend if the symptoms become worse while resting at the same altitude
For most travellers, the best way to avoid altitude illness is to plan a gradual ascent, with extra rest days at intermediate altitudes. If this is not possible, prescription drugs are available to prevent or alleviate the effect of altitude sickness if taken in advance.
How can I avoid getting altitude sickness: not everyone is susceptible to altitude illness, and there are currently no screening tests that predict whether someone is at greater risk for altitude illness. Susceptibility to altitude illness appears to be inherent in some way and not affected by training or physical fitness. How a traveller has responded in the past to exposure to high altitude is the most reliable guide for future trips but is not infallible.