Background: We aimed to examine whether using a high fraction of inspired oxygen (FIO 2 ) in the context of an individualised intra-and postoperative open-lung ventilation approach could decrease surgical site infection (SSI) in patients scheduled for abdominal surgery. Methods: We performed a multicentre, randomised controlled clinical trial in a network of 21 university hospitals from June 6, 2017 to July 19, 2018. Patients undergoing abdominal surgery were randomly assigned to receive a high (0.80) or conventional (0.3) FIO 2 during the intraoperative period and during the first 3 postoperative hours. All patients were mechanically ventilated with an open-lung strategy, which included recruitment manoeuvres and individualised positive end-expiratory pressure for the best respiratory-system compliance, and individualised continuous postoperative airway pressure for adequate peripheral oxyhaemoglobin saturation. The primary outcome was the prevalence of SSI within the first 7 postoperative days. The secondary outcomes were composites of systemic complications, length of intensive care and hospital stay, and 6-month mortality. Results: We enrolled 740 subjects: 371 in the high FIO 2 group and 369 in the low FIO 2 group. Data from 717 subjects were available for final analysis. The rate of SSI during the first postoperative week did not differ between high (8.9%) and low (9.4%) FIO 2 groups (relative risk [RR]: 0.94; 95% confidence interval [CI]: 0.59e1.50; P¼0.90]). Secondary outcomes, such as atelectasis (7.7% vs 9.8%; RR: 0.77; 95% CI: 0.48e1.25; P¼0.38) and myocardial ischaemia (0.6% [n¼2] vs 0% [n¼0]; P¼0.47) did not differ between groups. Conclusions: An oxygenation strategy using high FIO 2 compared with conventional FIO 2 did not reduce postoperative SSIs in abdominal surgery. No differences in secondary outcomes or adverse events were found. Clinical trial registration: NCT02776046.

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