A

Breathing 100 % O₂ for about 3 minutes of normal tidal breathing is the standard recommendation to achieve adequate denitrogenation and create an oxygen reserve before induction and tracheal intubation; this duration reliably attains an end-tidal O₂ ≥ 90 % in most patients, prolonging safe apnoea time [Bouroche & Bourgain, 2015, PMID 26044934; Tanoubi et al., 2009, PMID 19399574].