Acute Mountain Sickness
Acute mountain sickness (AMS) occurs when the body does not adapt quickly enough to reduced oxygen at altitude. It typically sets in above 2,500 metres and is common among trekkers heading to Nepal, Tibet, Bhutan, or the high plateaus of western China. Symptoms, headache, nausea, dizziness, and disturbed sleep, usually appear within hours of reaching elevation.
Key points
- Headache, nausea and poor sleep are the usual early symptoms, showing up within a few hours after gaining altitude.
- Climbing gradually, limiting how much sleeping altitude is gained each day once above 3,000 metres, best prevents the illness.
- One preventive medicine stimulates faster breathing, which lifts blood oxygen levels before symptoms have a chance to start.
- Confusion, an unsteady walk or a persistent cough at height can signal a more serious complication needing immediate descent.
Prevention and treatment at altitude
Ascending gradually (no more than 300-500 metres of sleeping elevation gain per day above 3,000 m) is the most reliable preventive measure. Staying well-hydrated and avoiding alcohol in the first 24-48 hours also helps.
Acetazolamide is the established medicine for both preventing and relieving AMS. It works by stimulating faster, deeper breathing, which raises blood oxygen levels. It is usually started one to two days before ascent.
Descent remains the definitive treatment for any severe or worsening AMS. Symptoms such as confusion, inability to walk straight, or a persistent dry cough at altitude warrant immediate descent and medical assessment, these can signal the more serious conditions of high-altitude cerebral or pulmonary oedema.