Dose–response relationship between intraoperative hyperoxia and long-term mortality according to the cumulative oxygen exposure during surgery: a scoping review

Introduction: Oxygen administration is a fundamental component of general anaesthesia and constitutes one of the most frequently used interventions in the intraoperative management of surgical patients. In many procedures, the fractions of inspired oxygen (FiO₂) administered substantially exceed physiological levels in order to prevent hypoxaemia and optimise tissue oxygenation. However, increasing evidence suggests that exposure to supranormal oxygen concentrations may induce adverse pathophysiological effects, including oxidative stress, endothelial dysfunction, systemic vasoconstriction and alterations in microcirculation. Although several studies have evaluated the effects of hyperoxia during the perioperative period, the available evidence regarding its impact on long-term clinical outcomes, particularly late mortality, remains limited and heterogeneous. Methods: A scoping review will be conducted in accordance with the methodological recommendations of the Joanna Briggs Institute and the reporting guidelines of PRISMA-ScR. The literature search will be performed in the PubMed, Scopus and Web of Science Core Collection databases. Studies evaluating adult patients undergoing surgery under general anaesthesia and analysing exposure to intraoperative hyperoxia using metrics such as fraction of inspired oxygen (FiO₂), arterial oxygen tension (PaO₂) or other measures related to cumulative oxygen exposure over time will be included. The study selection process will be performed independently by two reviewers using the Rayyan platform. Data extraction will be conducted using a standardised matrix developed in Microsoft Excel to collect bibliographic and methodological information, population characteristics, hyperoxia exposure metrics and reported mortality outcomes. Expected results: This review is expected to systematically map the available evidence regarding exposure to intraoperative hyperoxia and its potential association with long-term mortality. In particular, it aims to identify the different metrics used to quantify intraoperative hyperoxia, the methodological variability across studies and the patterns of association reported between intraoperative oxygen exposure and late mortality. This evidence mapping will help identify relevant knowledge gaps and contribute to guiding future research aimed at optimising intraoperative oxygenation strategies in perioperative anaesthesiology.