Fraction of inspired oxygen during general anesthesia for non-cardiac surgery: Systematic review and meta-analysis

Background: Controversy exists regarding the effects of a high versus a low intraoperative fraction of inspired oxygen (FiO₂ ) in adults undergoing general anesthesia. This systematic review and meta-analysis investigated the effect of a high versus a low FiO₂ on postoperative outcomes.

Methods: PubMed and Embase were searched on March 22, 2022 for randomized clinical trials investigating the effect of different FiO₂ levels in adults undergoing general anesthesia for non-cardiac surgery. Two investigators independently reviewed studies for relevance, extracted data, and assessed risk of bias. Meta-analyses were performed for relevant outcomes, and potential effect measure modification was assessed in subgroup analyses and meta-regression. The evidence certainty was evaluated using GRADE.

Results: This review included 25 original trials investigating the effect of a high (mostly 80%) versus a low (mostly 30%) FiO₂ . Risk of bias was intermediate for all trials. A high FiO₂ did not result in a significant reduction in surgical site infections (OR: 0.91, 95% CI 0.81-1.02 [p = .10]). No effect was found for all other included outcomes, including mortality (OR = 1.27, 95% CI: 0.90-1.79 [p = .18]) and hospital length of stay (mean difference = 0.03 days, 95% CI -0.25 to 0.30 [p = .84). Results from subgroup analyses and meta-regression did not identify any clear effect modifiers across outcomes. The certainty of evidence (GRADE) was rated as low for most outcomes.

Conclusions: In adults undergoing general anesthesia for non-cardiac surgery, a high FiO₂ did not improve outcomes including surgical site infections, length of stay, or mortality. However, the certainty of the evidence was assessed as low.