Noninvasive assessment of cerebral oxygenation during high altitude trekking in the Nepal Himalayas (2850-5600 m).

Mountain trekking is significantly increasing in popularity. Hypoxia seems to play a key role in the pathogenesis of acute mountain sickness (AMS). The purpose of this study was to investigate regional cerebral (rSO2) and peripheral (SaO2) oxygen saturation for the first time, during 22 days high altitude trekking (measurement points: 3450, 4450, 4750, 5050 and 2850 m) in the Khumbu region of Nepal with near infrared spectroscopy and pulse oximetry. We examined 17 healthy volunteers 19-65 years old (8 female, 9 male; mean age +/- SD, 46.1 +/- 13.1 years). RSO2 and SaO2 were significantly (p < 0.001, ANOVA, Tukey test) decreased at high altitudes (4450, 4750 and 5050 m). The decrease in cerebral oxygen saturation was more pronounced at higher altitudes than in the periphery (rSO2/SaO2 = 0.56 at 5050 m). At higher altitudes (> 4450 m), two subjects showed reversible symptoms of AMS. The present data indicates that acute reduction in rSO2 values might be a primary cause of AMS, however, further studies and analysis are necessary to correlate our findings with cerebral symptom scores.