Rate of ascent and acute mountain sickness at high altitude

Objective: To examine the effect of ascent rate on the induction of acute mountain sickness (AMS) in young adults during a climb to Jiaming Lake (3350 m) in Taiwan. Design: Prospective, nonrandomized. Setting: Climb from 2370 to 3350 m. Participants: Young adults (aged 18 to 26 years) (N = 91) chose to participate in either the fast ascent (3 days; n = 43) or slow ascent (4 days; n = 48) group (1 and 2). Assessment of Risk Factors: Two criteria were used to define AMS. A Lake Louise score $3 and Lake Louise criteria [in the setting of a recent gain in altitude, the presence of headache and at least 1 of gastrointestinal discomfort (anorexia, nausea, or vomiting), fatigue or weakness, dizziness or lightheadedness, or difficulty sleeping]. Main Outcome Measures: Heart rate, blood oxygen saturation (SaO2), and symptoms of AMS were monitored each morning and evening. Results: Baseline characteristics were similar between groups, except for significant differences in history of alcohol consumption (P = 0.009) and climbing experience above 3000 m (P, 0.001). The incidence of AMS was not associated with the rate of ascent. Acute mountain sickness was most prevalent in group 1 on day 2 in the evening and in group 2 on day 3 in the evening. In both groups, AMS correlated with the initial reduction in SaO2. Body mass index (BMI).24 kg/m2 was identified as a significant risk factor for AMS. Conclusions: The development of AMS was closely associated with an initial reduction in SaO2. A BMI.24 kg/m2 also contributed to the occurrence of AMS. Clinical Relevance: These findings indicate that factors other than ascent rate should be considered when trying to ameliorate the risk of AMS.