Rate of ascent and acute mountain sickness at high altitude.

Hsu, Tai-Yi; Weng, Yi-Ming; Chiu, Yu-Hui; Li, Wen-Cheng; Chen, Pang-Yen; Wang, Shih-Hao; Huang, Kuo-Feng; Kao, Wei-Fong; Chiu, Te-Fa; Chen, Jih-Chang

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/m 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/m 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.