Preoxygenation with high-flow nasal oxygen: the role of flow rate in safe apnoea time

High-flow nasal oxygen (HFNO) is increasingly used for preoxygenation, yet the optimal flow rate remains uncertain. Sjöblom and colleagues compared 45, 70, and 95 L min^-1 and found no significant differences in safe apnoea time when HFNO was stopped at apnoea onset and the airway left open to atmosphere. This commentary reflects on why, under their study design, higher flows might not be expected to extend safe apnoea time and shows that clinically relevant differences (≈2-3 min) cannot be excluded from the summary data. It places the findings within their physiological context and discusses why results may differ if HFNO is continued through apnoea, if patient positioning varies, or when patient-level factors are taken into account. It also emphasises that the absence of a statistically significant difference does not constitute evidence of equivalence and proposes a pragmatic approach to preoxygenation.