Treatment of acute mountain sickness by simulated descent: a randomised controlled trial.

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Abstract
OBJECTIVE--To evaluate the therapeutic efficacy of a portable hyperbaric chamber for treatment of acute mountain sickness. DESIGN--Controlled randomised trial over two mountaineering seasons. SETTING--High altitude research laboratory at 4559 m above sea level. SUBJECTS--64 climbers with acute mountain sickness randomly allocated to different treatments. INTERVENTIONS--One hour of treatment in the hyperbaric chamber at a pressure of 193 mbar or 20 mbar as control or bed rest. MAIN OUTCOME MEASURES--Symptoms of acute mountain sickness before, immediately after, and 12 hours after treatment. Permitted intake of analgesic and antiemetic drugs in the follow up period. RESULTS--Treatment with 193 mbar caused greater relief of symptoms than did control treatment or bed rest. During the 12 hour follow up period intake of analgesics was similar (58-80% of subjects in each group). Symptom scores had improved in all subjects after 12 hours with no significant differences between groups. CONCLUSIONS--One hour of treatment with 193 mbar in a portable hyperbaric chamber, corresponding to a descent of 2250 m, leads to a short term improvement in symptoms of acute mountain sickness but has no beneficial long term effects attributable to pressurisation.