Kalamaoo County

Health and Community Services Department


Acute Mountain Sickness (AMS)

The cause
High altitude holidays are increasingly popular. In South America they include crossing Andean passes often above 4000 meters. Trekkers in the Himalayas, especially in Nepal, often reach similar heights. Kilimanjaro in Tanzania and Mount Kenya are both more than 5000 meters.

Only those healthy and trained should attempt such expeditions, and if in doubt medical advice should be taken. All including the physically fit can get acute mountain sickness during rapid ascent if staying for more than 12 hours above 2500 meters. It affects all ages including children when the symptoms may be more difficult to recognize.

The altitude difference undergone in 24 hours is the determining factor. From 3000 meters and higher, the risk increases when the altitude difference between encampments exceeds 300 meters.


  • High Altitude: 2400m to 3658m. (e.g. Cochabamba in Bolivia = 2550m. Bogota in Columbia = 2645m. Quito in Ecuador = 2879m. Cuzco in Peru = 3225m)
  • Very High Altitude: 3658m to 5500m. (La Paz in Bolivia = 3658m. Lhasa in Tibet, China = 3685m. Base camps of Everest in Nepal = 5500m)
  • Extreme Altitude: 5500m to 8848m (e.g. the summit of Mount Everest).

Signs of mountain sickness
Early signs of acute mountain sickness include headache, nausea, loss of appetite and insomnia. If vertigo, vomiting, apathy, staggering and breathlessness occur, immediate accompanied descent is essential. Failing to descend may be fatal.

Avoid ascents of greater than 300 meters per day if starting from above 3000 meters. If early signs of mountain sickness appear, rest for a day at the same altitude. If they persist or increase, descend at least 500 meters.

Acetazolamide (Diamox) can be used to help prevent mountain sickness when a gradual ascent cannot be guaranteed. It should NOT be used as an alternative to a gradual ascent. It acts on acid-base balance and stimulates respiration. It should be combined with a good fluid intake. It should not normally be used in young children except under close medical supervision. Dose: 250mg bd. for adults. A smaller dose (125mg bd) is probably just as effective and gives less side effects.

Initially simple analgesia (e.g. paracetamol ) for headaches. Sleeping pills should be avoided if possible.

Acute mountain sickness with cerebral edema.
Immediate evacuation or descent at least 1000 meters; oxygen if available. (b) Dexamethasone (12-20 mg daily) or Prednisolone (40 mg daily).

High altitude pulmonary oedema.
Immediate evacuation or descent. If symptoms are acute and/or descent is impossible or delayed consider Nifedipine (20mg tds).

Useful addresses
For information sheets available to Doctors/Climbers/Trekkers contact the British Mountaineering Council, 177-179 Burton Road, Manchester, M20 2BB. Tel:0870 010 4848. Fax:0161 445 4500 web-site address: www.thebmc.co.uk

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