BACKGROUND: Administration of supplemental oxygen in the perioperative period is controversial, as it may increase long-term mortality. Our aim was to assess the association between 80% oxygen and occurrence of subsequent cancer in patients undergoing abdominal surgery in a post hoc analysis of the PROXI trial. METHODS: The 1386 patients in the PROXI trial underwent elective or emergency laparotomy between 2006 and 2008 with randomization to either 80% or 30% oxygen during and for 2 h after surgery. We retrieved follow-up status regarding vital status, new cancer diagnoses, and new histological cancer specimens. Data were analysed using the Cox proportional hazards model. RESULTS: Follow-up was complete in 1377 patients (99%) after a median of 3.9 yr. The primary outcome of new cancer diagnosis or new malignant histological specimen occurred in 140 of 678 patients (21%) in the 80% oxygen group vs 150 of 699 patients (21%) assigned to 30% oxygen; hazards ratio 1.06 [95% confidence interval (CI) 0.84, 1.34], P=0.62. Cancer-free survival was significantly shorter in the 80% oxygen group; hazards ratio 1.19 (95% CI 1.01, 1.42), P=0.04, as was the time between surgery and new cancer, median 335 vs 434 days in the 30% oxygen group. In patients with localized disease, non-significant differences in cancer and cancer-free survival were found with hazard ratios of 1.31 and 1.29, respectively. CONCLUSIONS: Although new cancers occurred at similar rate, the cancer-free survival was significantly shorter in the 80% oxygen group, but this did not appear to explain the excess mortality in the 80% oxygen group. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov (NCT01723280).
British Journal of Anaesthesia, 2014, Vol 113, Issue suppl. 1