If you're going to altitudes above 3000m, acute mountain sickness (AMS) is an issue. The biggest risk factor is going too high too quickly – follow a conservative acclimatisation schedule found in good trekking guides, and never go to a higher altitude when you have any symptoms that could be altitude related. There is no way to predict who will get altitude sickness, and it is quite often the younger, fitter members of a group who succumb.
Symptoms usually develop during the first 24 hours at altitude but may be delayed up to three weeks. Mild symptoms include the following:
- difficulty sleeping
- loss of appetite.
AMS may become more severe without warning and can be fatal. Severe symptoms include the following:
- a dry, irritative cough (which may progress to the production of pink, frothy sputum)
- severe headache
- lack of coordination and balance
- irrational behaviour
- loss of consciousness.
Treat mild symptoms by resting at the same altitude or lower until recovery, which usually takes a day or two. Paracetamol or aspirin can be taken for headaches. If symptoms persist or become worse, immediate descent is necessary; even 500m can help. Drug treatments should never be used to avoid descent or to enable further ascent.
The drugs acetazolamide (Diamox) and dexamethasone are recommended by some doctors for the prevention of AMS; however, their use is controversial. They can reduce the symptoms, but they may also mask warning signs; severe and fatal AMS has occurred in people taking these drugs.
To prevent AMS, carry out the following steps:
- ascend slowly – have frequent rest days, spending two to three nights at each rise of 1000m
- sleep at a lower altitude than the greatest height reached during the day, if possible. Above 3000m, don’t increase sleeping altitude by more than 300m daily
- drink extra fluids
- eat light, high-carbohydrate meals
- avoid alcohol and sedatives.