Rapid ascents of Mt. Everest: normobaric hypoxic pre-acclimatization.

BACKGROUND Acclimatization to high altitude is time consuming. An expedition to Mt. Everest (8848 m) requires roughly 8 weeks. Therefore it seems very attractive to reach the summit within three weeks from home, which is currently promised by some expedition tour operators. These rapid ascent expeditions are based on two main components, normobaric hypoxic training (NHT) prior to the expedition and the use of high flow supplemental oxygen (HFSO2). We attempted to assess the relative importance of these two elements. METHODS We evaluated the effect of NHT on the basis of the available information of these rapid ascent expeditions and our experiences made during an expedition to Manaslu (8163 m) where we used NHT for preacclimatization. To evaluate the effect of an increased O2-flow rate we calculated its effect for different activity levels at altitudes of 8000 m and above. RESULTS So far rapid ascents to Mt. Everest have been successful. The participants carried out 8 weeks of NHT, reaching sleeping altitudes equivalent to 7100 m and spent at least 300 hours in NH. At rest a flow rate of 2 l O2/min is sufficient to keep PIO2 close to 50 mmHg even at the summit. For physical exercise of about 80% VO2max at the summit 6 l O2/min are required to maintain a PIO2 above 50 mmHg. DISCUSSION NHT for preacclimatization seems to be the decisive element of the offered rapid ascent expeditions. An increased O2-flow rate of 8 l/min is not mandatory for climbing Mt Everest. CONCLUSIONS Preacclimatization using NH is far more important than the use of HFSO2. We think that NHT will be widely used in the future. The most effective regimen of preacclimatization in NH, the duration of each session and the optimal FIO2 are still unclear and require further studies.