To aid readability of the numerical data in our reviews, we round many percentages to the nearest whole number. In addition, we use a regular surveillance protocol to capture harms alerts from organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA), which are added to the reviews as required. We included systematic reviews of RCTs and RCTs where harms of an included intervention were studied applying the same study design criteria for inclusion as we did for benefits. We excluded individual RCTs that examined effects of simulated altitude in hypobaric chambers. We excluded RCTs if rates of ascent and absolute altitude were different between treatment groups. We excluded crossover trials that did not report pre-crossover results. For drug studies, we excluded all studies described as "open", "open label", not blinded, or single-blinded. There was no minimum length of follow-up required to include studies. RCTs had to contain 20 or more individuals of whom 80% or more were followed up. RCTs had to be at least single-blind for drug interventions, but open studies were acceptable for other options. Study design criteria for inclusion in this review were: published systematic reviews of RCTs and RCTs in any language. Selected studies were then sent to the contributor for additional assessment, using pre-determined criteria to identify relevant studies. Abstracts of the studies retrieved from the initial search were assessed by an information specialist. We also searched for retractions of studies included in the review. An additional search within the Cochrane Library was carried out for the Database of Abstracts of Reviews of Effects (DARE) and Health Technology Assessment (HTA) database. The following databases were used to identify studies for this systematic review: Medline 1966 to October 2009, Embase 1980 to October 2009, and The Cochrane Database of Systematic Reviews 2009, Issue 4. The overall odds ratio for developing acute mountain sickness in susceptible compared with non-susceptible people was 2.9 (95% CI 2.1 to 4.1).Ĭlinical Evidence search and appraisal October 2009. In non-susceptible people, the corresponding values were 31%, 16%, 11%, and 4%. It found that, in susceptible people (who had previously had acute mountain sickness at high altitude), the prevalence of acute mountain sickness was 58% with rapid ascent and no pre-exposure, 29% with pre-exposure only, 33% with slow ascent only, and 7% with both pre-exposure and slow ascent. In this study, pre-exposure was defined as having spent more than 4 days above 3000 m in the preceding 2 months, and slow ascent was defined as ascending in more than 3 days. One survey in Switzerland (827 mountaineers ascending to 4559 m) examined the effects of susceptibility, pre-exposure, and ascent rate on acute mountain sickness. One systematic review (search date 1999) comparing prophylactic agents versus placebo found that, among people receiving placebo, the incidence of acute mountain sickness was higher with a faster rate of ascent (54% of people at a mean ascent rate of 91 m/hour 73% at a mean ascent rate of 1268 m/hour 89% at a simulated ascent rate in a hypobaric chamber of 1647 m/hour). However, the study was too small to exclude these as risk factors, or to quantify risks reliably. It found no evidence of a difference in risk between men and women, or that previous episodes of altitude experience, load carried, or recent respiratory infections, affected risk. One survey in the Himalayas identified the rate of ascent and absolute height attained as the only risk factors for acute mountain sickness.
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