Altitude Sickness

Acute mountain sickness (AMS) is a condition that affects many travellers to high altitude. It is caused by a lack of oxygen and is especially common at heights above 2,500m. The main symptoms are headache, loss of appetite, nausea, vomiting and lethargy. The development of AMS is not dependent on age, gender or level of fitness.

The main danger with AMS is that it may progress to life threatening 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 with blood stained sputum) and excessive 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 final progression into a coma.

Prevention of Altitude Sickness

AMS is best prevented by ascending gradually. The usual recommendation when above 3,000m is to ascend on average no more than 300m each day and to stop for a day and rest every 1000m or every 3 days.

A drug called acetazolamide (Diamox®) has been shown to reduce the incidence and severity of AMS, however this drug is not routinely recommended. The usual dose is 250mg tablet twice a day or 500mg sustained release tablet nightly at least the day before ascending above 2,500m. Some doctors are now recommending halving this dose to 125mg twice a day to reduce side effects (although this dose has not been studied extensively). Acetazolamide can make you pass urine more than usual, can cause ‘pins and needles’ in the fingers and toes, and can make fizzy drinks taste flat. When acetazolamide is taken, it should be continued until descent.

Treatment of Altitude Sickness

The principles of treatment of AMS are as follows

  • stop further ascent 
  • descend if there is no improvement or if the condition worsens
  • descend immediately if there are symptoms or signs of HAPE or HACE
  • do not leave anyone with AMS on their own. 

The best treatment for all forms of altitude illness is descent. However in mild forms of AMS rest alone may be sufficient. Anyone with symptoms of AMS must not ascend any further until symptoms have disappeared. Painkillers such as paracetamol may be given for a headache.

Ref: Pollard, A.J; Murdoch, D.R, (2003), ‘The High Altitude Medicine Handbook’