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Many travellers to high altitude can be affected by Acute Mountain Sickness (AMS). This condition is caused by the reduced partial pressure of oxygen in the air at altitude and is common at heights above 2500m.

 Here are the heights of some well known travel destinations:

Most people feel at least a little unwell if they drive, fly or travel by train from sea level to 3500m. Over 50% of travellers develop some form of AMS at 3500m, but almost all will do so if they ascend rapidly to 5000m. A small percentage of people will develop symptoms at heights between 1500 and 2500m.

Altitude sickness is not dependent on age, level of fitness, or whether the person has experienced it before; anybody can experience this condition.

Headache, fatigue, unusual breathlessness on exertion, palpitations, loss of appetite, nausea, vomiting, dizziness, difficulty sleeping and irregular breathing during sleep are the symptoms of AMS, which usually develop during the first 36 hours at altitude, typically within 6-12 hours, not immediately on arrival.

The most important factor in reducing the risk of AMS is to ascend slowly, allowing time to acclimatise. When first arriving at a location at high altitude rest for 2-3 days before ascending further, with no strenuous activities. Ascent should then be gradual - no more than a 300m increase in sleeping altitude per day (with a rest day at the same altitude every third day) and spending at least a week above 3500m before sleeping at 5000m.

If symptoms of AMS develop rest and stopping further ascent are essential. Usually symptoms will improve within 2-3 days as the body becomes acclimatised, as long as no further ascent is made. Headache can be treated with simple analgesics such as paracetamol or ibuprofen at the recommended dosage. The person should descend to a lower altitude if there is no improvement or if their symptoms worsen. Someone with AMS should not be left alone, as their condition may deteriorate without them realising it.

The main danger with AMS is that it may develop into more serious forms of altitude illness called high altitude pulmonary oedema (HAPE) and high altitude cerebral oedema (HACE).  In HAPE, fluid accumulates in the lungs and symptoms include shortness of breath (even at rest), cough (sometimes bringing up blood stained or pinky fluid) and extreme tiredness.  In HACE, excessive fluid causes the brain to swell leading to symptoms such as worsening headache, unsteadiness on the feet, altered behaviour, hallucinations, disorientation, confusion and drowsiness, progressing to coma.  HAPE and HACE can be life-threatening, so these symptoms should be treated as an emergency, with immediate descent and urgent medical treatment.

There has been much research on the medication acetazolamide (Diamox), a drug normally used to reduce fluid retention. Diamox can prevent the development of Acute Mountain Sickness if taken for several days before ascent, however it is not routinely recommended due to side effects and potential risks. The important point to understand is that it only relieves the symptoms of AMS and will not prevent the condition worsening should a sufferer fail to descend or rest. Its use to allow continued or rapid ascent is extremely dangerous, possibly masking warning signs of more serious HAPE and HACE. Diamox should only be used for the prevention or relief of AMS in a controlled fashion, to allow descent and rest - the only cure for AMS. If you do decide to take Diamox, you should consult your GP or a doctor experienced in mountain medicine.

Also remember to apply a high factor sunblock to all exposed skin areas even if it is cold or cloudy - high altitude increases UV exposure by about 15% for every 1000 metres, plus UV rays reflect off snow and ice and can cause burning in areas not usually exposed to a burn risk such as the underside of the chin and ears.