Acute mountain sickness: influence of susceptibility, preexposure, and ascent rate

We examined the interaction of various established risk factors for acute mountain sickness (AMS) in a setting relevant for mountaineering and trekking.

Questionnaires were obtained from 827 mountaineers on the day of arrival at the Capanna Margherita (4559 m) and on the next morning. Susceptibility to AMS was assessed by type and frequency of symptoms during previous exposures. AMS was defined as an AMS-C score >/= 0.7 (environmental symptom questionnaire) on the morning after arrival at 4559 m. Preexposure was defined as having spent more than 4 d above 3000 m during the 2 months preceding the climb to the Capanna Margherita. Slow ascent was defined as ascending in more than 3 d. A risk model was developed by multiple logistic regression and prospectively validated on independent data.

In susceptible individuals, the prevalence of AMS was 58% with rapid ascent and no preexposure, 29% with preexposure only, 33% with slow ascent only, and 7% with both preexposure and slow ascent. The corresponding values for nonsusceptible individuals were 31%, 16%, 11%, and 4%. The overall odds ratio for developing AMS in susceptible versus nonsusceptible individuals was 2.9 (95% confidence interval, 2.1-4.1). Age, gender, training, body mass index, alcohol intake, and cigarette smoking had no significant effect in bivariate analyses or in multivariate logistic regressions.

Individual susceptibility, rate of ascent, and preexposure are the major, independent determinants for prevalence of AMS.