Supplemental Intraoperative Oxygen Does Not Promote Acute Kidney Injury or Cardiovascular Complications After Noncardiac Surgery: Subanalysis of an Alternating Intervention Trial

BACKGROUND: Perioperative hyperoxia has been recommended by the World Health Organization and the Centers for Disease Control and Prevention for the prevention of surgical site infections. Based on animal studies and physiological concerns, the kidneys and heart may be at risk from hyperoxia. We therefore conducted 2 unplanned subanalyses of a previous alternating cohort trial in which patients having colorectal surgery were assigned to either 30% or 80% inspired intraoperative oxygen. Specifically, we tested 2 coprimary hypotheses: (1) hyperoxia increases the incidence of acute kidney injury (AKI) within 7 postoperative days (PODs); and (2) hyperoxia worsens a composite of myocardial injury, in-hospital cardiac arrest, and 30-day mortality. METHODS: The underlying controlled trial included 5749 colorectal surgeries in 4481 patients, with the exposure alternating between 30% and 80% fraction of inspired oxygen (FIO2) during general anesthesia at 2-week intervals over a period of 39 months. AKI was defined as a 1.5-fold increase in creatinine from the preoperative level to the highest value measured during the initial 7 PODs. Myocardial injury was defined by fourth-generation troponin-T level >0.03 ng/mL. We assessed the effect of 80% vs 30% oxygen on the outcomes using generalized estimating equation (GEE) logistic models that adjusted for the possible within-patient correlation across multiple potential operations for a patient on different visits. RESULTS: For the AKI outcome, 2522 surgeries were allocated to 80% oxygen and 2552 to 30% oxygen. Hyperoxia had no effect on the primary outcome of postoperative AKI, with an incidence of 7.7% in the 80% oxygen group and 7.7% in the 30% oxygen group (relative risk = 0.99; 95% confidence interval [CI], 0.82-1.2; P = .95). One thousand six hundred forty-seven surgeries (all with scheduled troponin monitoring) were analyzed for the composite cardiovascular outcome. Hyperoxia had no effect on the collapsed composite of myocardial injury, cardiac arrest, and 30-day mortality, nor on any of its components (estimated relative risk = 0.71; 95% CI, 0.44-1.16; P = .17). CONCLUSIONS: We found no evidence that intraoperative hyperoxia causes AKI or cardiovascular complications in adults undergoing colorectal surgery. Consequently, we suggest that clinicians select intraoperative inspired oxygen fraction based on other considerations.