Preoxygenation with high-flow nasal oxygen at various flow rates in elective surgical patients: a prospective,...

High-flow nasal oxygen (HFNO) is increasingly used for preoxygenation. Previous studies of preoxygenation have explored flow rates below 60 L min^-1. This study aimed to compare different HFNO flow rates during preoxygenation to identify the most effective flow rate for clinical use.

This randomised trial included patients aged 18-84 yr of ASA physical status 1-3 scheduled for elective surgery. Preoxygenation was conducted using HFNO at randomised flow rates of 45, 70, or 95 L min^-1. After preoxygenation, patients rated their level of preoxygenation-related discomfort. HFNO was discontinued at apnoea start. After intubation, apnoea was maintained until Spo₂ reached 93%. Primary outcome was apnoea time until Spo₂=93%. Secondary outcomes were Pao₂ levels during preoxygenation and preoxygenation-related discomfort.

Of 72 participants included in the final analysis, baseline characteristics were similar and the mean duration of preoxygenation was 250 s in all three groups. Apnoea times did not differ, with median durations of 472, 523, and 483 s for 45, 70, and 95 L min^-1, respectively (P=0.59). At apnoea onset, 95 L min^-1 produced higher Pao₂ than 45 L min^-1. No other differences in Pao₂ were observed during preoxygenation. The level of discomfort was lower for 45 L min^-1 compared with 70 and 95 L min^-1.

There was no difference in the safe apnoea time between preoxygenation with the three flow rates. As 45 L min^-1 generated the least discomfort while providing preoxygenation effectiveness comparable with higher flow rates, increasing preoxygenation flow rate from 45 to 70 L min^-1 will likely not prolong safe apnoea time.

NCT06736132.