Bhutan - Lindsay Brown [225]
ACCLIMATISATION
With an increase in altitude, the human body needs time to develop physiological mechanisms to cope with the decreased oxygen. This process of acclimatisation is still not fully understood, but is known to involve modifications in breathing patterns and heart rate induced by the autonomic nervous system, and an increase in the blood’s oxygen-carrying capabilities. These compensatory mechanisms usually take about one to three days to develop at a particular altitude. Once you are acclimatised to a given height you are unlikely to get AMS at that height, but you can still get ill when you travel higher. If the ascent is too high and too fast, these compensatory reactions may not kick into gear fast enough.
SYMPTOMS
Mild symptoms of AMS are very common in travellers visiting high altitudes, and usually develop during the first 24 hours at altitude. Most visitors to Tibet will suffer from some symptoms; these will generally disappear through acclimatisation in several hours to several days.
Symptoms tend to be worse at night and include headache, dizziness, lethargy, loss of appetite, nausea, breathlessness and irritability. Difficulty sleeping is another common symptom.
AMS may become more serious without warning and can be fatal. Symptoms are caused by the accumulation of fluid in the lungs and brain, and include breathlessness at rest, a dry irritative cough (which may progress to the production of pink, frothy sputum), severe headache, lack of coordination (typically leading to a ‘drunken walk’), confusion, irrational behaviour, vomiting and eventually unconsciousness.
The symptoms of AMS, however mild, are a warning – be sure to take them seriously! Trekkers should keep an eye on each other as those experiencing symptoms, especially severe symptoms, may not be in a position to recognise them. One thing to note is that while the symptoms of mild AMS often precede those of severe AMS, this is not always the case. Severe AMS can strike with little or no warning.
PREVENTION
To prevent acute mountain sickness:
Ascend slowly. Have frequent rest days, spending two to three nights at each rise of 1000m. If you reach a high altitude by trekking, acclimatisation takes place gradually and you are less likely to be affected than if you fly directly to high altitude.
Trekkers should bear in mind the climber’s adage ‘Climb high, sleep low’. It is always wise to sleep at a lower altitude than the greatest height reached during the day. High day climbs followed by a descent back to lower altitudes for the night are good preparation for trekking at high altitude. Also, once above 3000m, care should be taken not to increase the sleeping altitude by more than 400m per day. If the terrain won’t allow for less than 400m of elevation gain, be ready to take an extra day off before tackling the climb.
Drink extra fluids. The mountain air is dry and cold, and moisture is lost as you breathe. Evaporation of sweat may occur unnoticed and result in dehydration.
Eat light, high-carbohydrate meals for more energy.
Avoid alcohol as it may increase the risk of dehydration, and don’t smoke.
Avoid sedatives.
When trekking, take a day off to rest and acclimatise if feeling over-tired. If you or anyone else in your party is having a tough time, make allowances for unscheduled stops.
Don’t push yourself when climbing up to passes; rather, take plenty of breaks. You can usually get over the pass as easily tomorrow as you can today. Try to plan your itinerary so that long ascents can be divided into two or more days. Given the complexity and unknown variables involved with AMS and acclimatisation, trekkers should always err on the side of caution and ascend mountains slowly.
TREATMENT
Treat mild symptoms by resting at the same altitude until recovery, usually a day or two. Take paracetamol or aspirin for headaches.