Effect of inspiratory oxygen fraction and lung recruitment maneuvers in patients undergoing abdominal surgery (ORMA): study protocol for a multi-center, randomized, controlled trial in a 2 × 2 factorial design

Postoperative pulmonary complications (PPCs) are common among patients undergoing abdominal surgery. Despite the established benefits of lung-protective ventilation strategies in preventing PPCs, the optimal inspiratory oxygen fraction (FiO 2 ) and the role of recruitment maneuvers (RMs) in the strategy remain controversial. This trial aims to evaluate the effects of different FiO 2 levels and RMs on the incidence of pulmonary complications following abdominal surgery. This is a multi-center, 2 × 2 factorial, randomized, controlled trial involving 1536 patients at intermediate-to-high risk of PPCs undergoing major abdominal surgery. Participants will be randomly assigned (1:1:1:1) to receive lung-protective ventilation with either 80% FiO 2 or the minimum FiO 2 required to maintain SpO 2 ≥ 94%, with or without standardized RMs. All patients will follow an enhanced recovery after surgery protocol. The primary outcome is the incidence of pulmonary complications within the first 7 postoperative days, including respiratory infection, respiratory failure, atelectasis, and clinically significant pleural effusion. Secondary outcomes include the severity grade of PPCs, incidence of PPCs within 30 days, and other clinical endpoints. The use of conservative FiO 2 or standardized RMs within a lung-protective ventilation strategy is anticipated to reduce pulmonary complications in at-risk patients. The trial’s design, enrollment strategy, and outcome measures are expected to yield clinically relevant results and contribute to optimizing perioperative mechanical ventilation. Chinese Clinical Trial Registry ChiCTR2400092953. Prospectively registered on 26 November 2024. ( https://www.chictr.org.cn/bin/project/edit?pid=250812 ).