Hanouz JL, et al. - In this randomised crossover study including 50 healthy volunteers, researchers compared the end-tidal fraction of oxygen (ETO₂) following a 3 min pre-oxygenation with high-flow nasal oxygen (HFNO) and face mask. In a random manner, they pre-oxygenated participants through spontaneous breathing 100% oxygen in a face mask and with HFNO (mouth closed, heated and humidified gas flow at 60 l min^–1). They continuously measured the ETO₂ in the face mask group. They quickly exchanged nasal cannula with a face mask, in the HFNO group, while the subject held their breath at end inspiration. In this group, they measured ETO₂ after a deep expiration. Findings demonstrated the non-reliability of pre-oxygenation with HFNO as a method of pre-oxygenation before the induction of anaesthesia.