The authors concluded that supplemental perioperative oxygenation was beneficial in prevention of surgical site infection in patients who underwent colorectal surgery, but since there was heterogeneity among studies additional research was required. In view of the unexplained differences in results among studies, the authors’ conclusions about the benefits of supplemental oxygenation may not be reliable.

To evaluate the efficacy of supplemental perioperative oxygenation on surgical site infection in patients who underwent colorectal surgery.

PubMed (including MEDLINE), Current Contents, CINAHL, DARE and the Cochrane Library were searched from inception to September 2007. Search terms were reported. No language restrictions were applied. An additional search was undertaken using the Google search engine. ClinicalTrials.com and reference lists were searched and experts in the field were contacted for details of any unpublished studies.

Randomised controlled trials (RCTs) that compared supplemental perioperative oxygenation with placebo or standard care in patients who underwent colorectal surgery and evaluated surgical site infection were eligible for inclusion. The reviewers accepted authors’ definitions of surgical site infection. The review also assessed mortality and length of hospital stay.

The included studies compared 80% oxygen in the supplemental group with 30% or 35% oxygen in the control group. In most studies supplemental oxygenation was administered during and for two hours after surgery. Oxygen was given using a non-rebreathing face mask with a reservoir. Where reported, patients ranged in age from 18 to 80 years and underwent elective colorectal surgery. Other measures used to reduce the risk of surgical site infection included mechanical bowel preparation with and without antibiotics; studies differed in their use of antibiotics. Studies used different definition of surgical site infection. Duration of follow-up ranged from two to four weeks.

Two reviewers independently selected studies and resolved disagreements by discussion.

Validity was assessed using the method of randomisation, allocation concealment, blinding, losses to follow-up and use of intention-to-treat analysis. The authors did not state how many reviewers assessed validity.

A standard form was used to extract data on adverse effects and incidence of surgical site infection, mortality and length of intensive care unit stay. Data were extracted only for patients who underwent colorectal surgery.

The authors stated neither how data were extracted for the review nor how many reviewers performed the data extraction.

Pooled relative risks (RR) and 95% confidence intervals (CI) were calculated using the DerSimonian and Laird random-effects model and the fixed-effect Mantel-Haenszel method. Heterogeneity was assessed using the Q and the I² statistics. Analysis of surgical site infection was repeated after excluding the study that accounted for the heterogeneity. Potential reasons for this heterogeneity were discussed. Publication bias was assessed using a funnel plot and Egger’s test.

Four RCTs were included (n=989). All four studies reported randomisation methods, three reported allocation concealment, three were double-blinded and in the fourth the outcome assessor for surgical site infection was blinded to the treatment group. Two studies used intention-to-treat analysis. Three studies reported losses to follow-up.

Supplemental oxygenation was associated with a statistically significant reduction in surgical site infection using a fixed-effect model (RR 0.70, 95% CI 0.52 to 0.94). There was no significant difference between treatments when a random effects model was used (RR 0.74, 95% CI 0.39 to 1.43). The authors stated in the results section that moderate to heterogeneity was found (I²=77%).

Two studies reported a statistically significant reduction in surgical site infection in the supplemental oxygenation group, one reported no significant difference between treatment groups and one reported a significantly higher surgical site infection rate in the supplemental oxygenation group; this last study accounted for all of the heterogeneity. After removal of the study that accounted for the heterogeneity, the relative risk of surgical site infection associated with supplemental oxygenation was 0.55 (95% CI 0.38 to 0.80). It was unclear whether a fixed-effect or random-effects model was used for this analysis.

There were no significant differences between treatment in duration of hospital stay (three studies) or mortality (two studies).

There was no evidence of publication bias.

Supplemental perioperative oxygenation was beneficial for prevention of surgical site infection in patients who underwent colorectal surgery. Since heterogeneity among studies was present additional RCTs were required.

The review question was clearly stated and inclusion criteria were appropriately defined. Several relevant sources were searched and attempts made to minimise publication and language biases. No evidence of publication bias was found, but since there were only four studies the assessment was of limited value. Appropriate methods were used to minimise reviewer error and bias during study selection; it was unclear whether similar methods were used for data extraction and validity assessment. Only RCTs were included. Validity was assessed and results were reported. Data were pooled using meta-analysis and heterogeneity was assessed. The heterogeneity and inconsistency of results from the four included studies suggested that a summary measure of treatment effect may not have been appropriate. Potential reasons for differing results among studies were discussed, but the heterogeneity remained unexplained. In view of the unexplained differences in results among studies, the authors’ conclusions about the benefits of supplemental oxygenation may not be reliable.

Practice: The authors stated that supplemental perioperative oxygenation (80%) should be used in all patients who undergo colorectal surgery until results from further studies are available; surgical site infection rates in patients who receive this treatment should be carefully monitored so that any increase in surgical site infection can be detected quickly.

Research: The authors stated that further research was required to evaluate the adverse effects of supplemental oxygenation and the cost-effectiveness of this intervention.

Not stated.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.