• Jean-Luc Hanouz, David Lhermitte, Jean-Louis Gérard, and Marc Olivier Fischer.
• From the Department of Anaesthesia and Intensive Care Medicine, Caen University Hospital, Caen, France.
• Eur J Anaesthesiol. 2019 May 1; 36 (5): 335-341.

BackgroundHigh-flow nasal oxygen (HFNO) therapy has been proposed for pre-oxygenation before intubation, but the end-tidal fraction of oxygen (ETO2) obtained remains unknown.Objective(S)To compare the ETO2 following a 3 min pre-oxygenation with HFNO and face mask.SettingOperating room in a primary university hospital.DesignA randomised crossover study.ParticipantsFifty healthy volunteers.InterventionsParticipants were randomly pre-oxygenated through spontaneous breathing 100% oxygen in a face mask and with HFNO (mouth closed, heated and humidified gas flow at 60 l min). In the face mask group, the ETO2 was measured continuously. In the HFNO group, the nasal cannula was quickly exchanged with a face mask while the subject held their breath at end inspiration and the ETO2 was measured after a deep expiration. The protocol ended when ETO2 reached 90% or otherwise at 6 min.Main Outcome MeasuresThe primary endpoint was the ETO2 after 3 min of pre-oxygenation. Secondary endpoints were the proportion of participants with an ETO2 at least 90% and the time until the ETO2 at least 90%.ResultsThe ETO2 after 3 min of pre-oxygenation was 89 (2) % and 77 (12) % in the face mask and HFNO groups [difference 12% (95% confidence interval, 95% CI: 8 to 15]; P < 0.001), respectively. After 3 min of pre-oxygenation, 54 and 4% (P < 0.001) of volunteers had an ETO2 at least 90% in the face-mask and HFNO groups, respectively. After 6 min of pre-oxygenation, 96 and 46% (P < 0.001) of volunteers had an ETO2 at least 90% in the face-mask and HFNO groups, respectively. In the face mask group, the hazard ratio to achieve an ETO2 of 90% was 5.3 (95% CI: 3.2 to 8.9; P < 0.001).ConclusionOur study demonstrates that pre-oxygenation with HFNO is not a reliable method of pre-oxygenation before the induction of anaesthesia.Trial Registrationclinical trial NCT03399695.

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