• M G Mythen, R C N McMorrow, J S Windsor, N D Hart, P Richards, G W Rodway, V Y Ahuja, M J O'Dwyer, and Caudwell Xtreme Everest Research Group.
• UCL Centre for Altitude Space and Extreme Environment Medicine, UCL Institute of Child Health, University College London, London, UK. mcmorrow.roger@gmail.com
• Anaesthesia. 2012 Aug 1;67(8):875-80.

AbstractWe present a randomised, controlled, crossover trial of the Caudwell Xtreme Everest (CXE) closed circuit breathing system vs an open circuit and ambient air control in six healthy, hypoxic volunteers at rest and exercise at Everest Base Camp, at 5300 m. Compared with control, arterial oxygen saturations were improved at rest with both circuits. There was no difference in the magnitude of this improvement as both circuits restored median (IQR [range]) saturation from 75%, (69.5-78.9 [68-80]%) to > 99.8% (p = 0.028). During exercise, the CXE closed circuit improved median (IQR [range]) saturation from a baseline of 70.8% (63.8-74.5 [57-76]%) to 98.8% (96.5-100 [95-100]%) vs the open circuit improvement to 87.5%, (84.1-88.6 [82-89]%; p = 0.028). These data demonstrate the inverse relationship between supply and demand with open circuits and suggest that ambulatory closed circuits may offer twin advantages of supplying higher inspired oxygen concentrations and/or economy of gas use for exercising hypoxic adults.Anaesthesia © 2012 The Association of Anaesthetists of Great Britain and Ireland.

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