Background: A follow-up analysis from a large trial of oxygen and surgical-site infections reported increased long-term mortality among patients receiving supplemental oxygen, especially those having cancer surgery. Although concerning, there is no obvious mechanism linking oxygen to long-term mortality. We thus tested the hypothesis that supplemental oxygen does not increase long-term mortality in patients undergoing colorectal surgery. Secondarily, we evaluated whether the effect of supplemental oxygen on mortality depended on cancer status.
Methods: Mortality data were obtained for 927 patients who participated in 2 randomized trials evaluating the effect of supplemental oxygen on wound infection. We assessed the effect of 80% vs 30% oxygen on long-term mortality across 4 clinical sites in the 2 trials using a Cox proportional hazards regression model stratified by study and site. Kaplan-Meier survival estimates were calculated for each trial. Finally, we report site-stratified hazard ratios for patients with and without cancer at baseline.
Results: There was no effect of 80% vs 30% oxygen on mortality, with an overall site-stratified hazard ratio of 0.93 (95% confidence interval [CI], 0.72-1.20; P = 0.57). The treatment effect was consistent across the 2 original studies (interaction P = 0.88) and across the 4 sites (P = 0.84). There was no difference between patients with (n = 451) and without (n = 450) cancer (interaction P = 0.51), with hazard ratio of 0.85 (95% CI, 0.64-1.1) for cancer patients and 0.97 (0.53-1.8) for noncancer patients.
Conclusions: In contrast to the only previous publication, we found that supplemental oxygen had no influence on long-term mortality in the overall surgical population or in patients having cancer surgery.