Acute mountain sickness and ascent rates in trekkers above 2500 m in the Nepali Himalaya.

INTRODUCTION: The aim of this study was to ascertain the incidence of acute mountain sickness (AMS) at different altitudes in the Solu-Khumbu. This was a pilot to examine the feasibility of investigating demographic, behavioral, and physiological factors related to the etiology of AMS and to assess the region's suitability for a future study.
METHODS: A convenience sample of 150 recreational trekkers staying in teahouses was interviewed at altitudes above 2500 m. Two interviews were performed, firstly in the evening and then the subsequent morning. Trekker's age, gender, ascent profile, and use of acetazolamide were noted. A Lake Louise score was calculated to determine the presence of AMS.
RESULTS: The incidence of AMS was 0% at 2500-3000 m, 10% between 3000-4000 m, 15% between 4000-4500 m, 51% between 4500-5000 m, and 34% over 5000 m. There was no significant association between age or gender and the altitude studied or incidence of AMS. Subjects with AMS ascended significantly further in the preceding 72 h than subjects without AMS, with a mean altitude gained of 846 m vs. 722 m. DISCUSSION: We concur with the literature that incidence of AMS increases with altitude. We found an abrupt increase in incidence over 4500 m. This appears to be a new finding. A future study examining factors predisposing to AMS would be most effectively performed above 4500 m. No association was found between age or gender and AMS. Mean vertical ascent gained in the previous 72 h was significantly higher among the trekkers with AMS but remained within recommended guidelines.