Effects of perioperative oxygen concentration on oxidative stress in adult surgical patients: a systematic review

Background: the fraction of inspired oxygen (FIO2) administered during general anaesthesia varies widely despite in-ternational recommendations to administer FIO20.8 to all anaesthetised patients to reduce surgical site infections (SSIs).Anaesthetists remain concerned that high FIO2administration intraoperatively may increase harm, possibly throughincreased oxidative damage. In previous systematic reviews associations between FIO2and SSIs have been inconsistent,but none have examined how FIO2affects perioperative oxidative stress. We aimed to address this uncertainty byreviewing the available literature.Methods: EMBASE, MEDLINE, and Cochrane databases were searched from inception to March 9, 2020 for RCTscomparing higher with lower perioperative FIO2and quantifying oxidative stress in adults undergoing noncardiac sur-gery. Candidate studies were independently screened by two reviewers and references hand-searched. Methodologicalquality was assessed using the Cochrane Collaboration Risk of Bias tool.Results:from 19 438 initial results, seven trials (n¼422) were included. Four studies reported markers of oxidative stressduring Caesarean section (n¼328) and three reported oxidative stress during elective colon surgery (n¼94). Risk of biaswas low (four studies) to moderate (three studies). Pooled results suggested high FIO2was associated with greatermalondialdehyde, protein-carbonyl concentrations and reduced xanthine oxidase concentrations, together with reducedantioxidant markers such as superoxide dismutase and total sulfhydryl levels although total antioxidant status wasunchanged.Conclusions: higher FIO2may be associated with elevated oxidative stress during surgery. However, limited studies havespecifically reported biomarkers of oxidation. Given the current clinical controversy concerning perioperative oxygentherapy, further research is urgently needed in this area