title: Risk of new or recurrent cancer after a high perioperative inspiratory oxygen fraction during abdominal surgery.
abstract: 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.
  
  
  BACKGROUND
  ClinicalTrials.gov (NCT01723280).
authors.affiliation: Department of Anaesthesiology, Herlev Hospital, University of Copenhagen, Herlev Ringvej 75, DK-2730 Herlev, Denmark christianmeyhoff@gmail.com.
authors.forename: C S
authors.initials: CS
authors.lastname: Meyhoff
authors.affiliation: Digestive Disease Center, Bispebjerg Hospital, University of Copenhagen, Bispebjerg Bakke 23, DK-2400 Copenhagen NV, Denmark.
authors.forename: L N
authors.initials: LN
authors.lastname: Jorgensen
authors.affiliation: Copenhagen Trial Unit, Centre for Clinical Intervention Research and.
authors.forename: J
authors.initials: J
authors.lastname: Wetterslev
authors.affiliation: The Research Unit for General Practice and Section of General Practice, Department of Public Health, University of Copenhagen, Øster Farimagsgade 5, DK-1014 Copenhagen K, Denmark.
authors.forename: V D
authors.initials: VD
authors.lastname: Siersma
authors.affiliation: Department of Anaesthesia, Centre of Head and Orthopaedics, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark.
authors.forename: L S
authors.initials: LS
authors.lastname: Rasmussen
mesh_terms: D000005:Abdomen / Q000601:surgery*; D000008:Abdominal Neoplasms / Q000453:epidemiology / Q000601:surgery; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003718:Denmark / Q000453:epidemiology; D018572:Disease-Free Survival; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007813:Laparotomy / Q000009:adverse effects / Q000401:mortality; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000453:epidemiology / Q000209:etiology*; D010102:Oxygen Inhalation Therapy / Q000009:adverse effects* / Q000379:methods / Q000401:mortality; D019990:Perioperative Care / Q000009:adverse effects* / Q000379:methods / Q000401:mortality; D012008:Recurrence; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors
keywords: laparotomy; neoplasms; oxygen therapy; postoperative complications