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

AbstractObjective-To evaluate the therapeutic efficacy of a portable hyperbaric chamber for treatment of acute mountain sickness.Design-Controlied randomised trial over two mountaineering seasons.Setting-High altitude research laboratory at 4559 m above sea level.Subjects-64 climbers with acute mountain sick ness randomly allocated to different treatments.Interventions-One hour oftreatment in the hyper baric 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 betweengroups.Conclusions-One hour of treatment with 193 mbar in a portable hyperbaric chamber, correspond ing to a descent of 2250 m, leads to a short term improvement in symptoms of acute mountain sick ness but has no beneficial long term effects attribut able to pressurisation.