High-flow nasal oxygen versus conventional oxygen after bariatric surgery in adults with class II–III obesity: a randomized trial with factorial exploration of flow and duration

Adults with class II–III obesity are prone to postanesthesia hypoxemia. Whether early post-extubation high-flow nasal oxygen (HFNO) improves postoperative oxygenation compared with conventional oxygen therapy (COT) after bariatric surgery remains uncertain. Adults with class II–III obesity undergoing laparoscopic bariatric surgery were randomized to COT or HFNO. Participants assigned to HFNO were further randomized to one of four protocols combining flow rates of 40–60 L·min⁻¹ with protocol durations of 30–60 min. The primary endpoint was PaO₂/FiO₂ at T2, measured after completion of the allocated oxygen-therapy period. Of 148 participants randomized under Protocol Version 2.0, 143 were included in the modified intention-to-treat analysis (HFNO, n = 102; COT, n = 41). At T2, PaO₂/FiO₂ was higher with HFNO than with COT (median [IQR], 375 [330–405] vs. 217 [193.5–230] mmHg; Hodges–Lehmann median difference, 153 mmHg [95% CI, 133–168]; P < 0.001). Absolute T2 PaO₂ was 150.0 [132.2–161.5] versus 86.8 [77.6–92.0] mmHg (Hodges–Lehmann median difference, 61.2 mmHg [bootstrap 95% CI, 54.0–67.2]; P < 0.001). Because effective FiO₂ was not measured in the COT group, the PaO₂/FiO₂ estimate compares assigned oxygen strategies rather than identical delivered FiO₂ levels. A bounded sensitivity analysis varying assumed COT FiO₂ from 0.28 to 0.40 attenuated the estimated PaO₂/FiO₂ difference from approximately 61 to 153 mmHg. Fewer early hypoxemic events were observed with HFNO, although observation duration differed across protocols. Exploratory within-HFNO findings remained hypothesis-generating because protocol-duration comparisons were confounded by later assessment of the 60-min protocols. Dyspnea VAS, modified Aldrete score, and length of stay showed only small absolute differences. In patients with class II–III obesity after laparoscopic bariatric surgery, early HFNO improved short-term oxygenation and lung aeration and was associated with fewer early hypoxemic events compared with COT. Differences among HFNO settings were exploratory and should not be considered definitive. Chinese Clinical Trial Registry, ChiCTR2400091922. Registered on 6 November 2024; retrospectively registered.