Figure 4

Trial sequential analysis of all trials irrespective of adjuvant inhaled gases. The effect of 80% oxygen vs. 30% oxygen on surgical site infections calculated in cumulative meta-analysis of all trials irrespective adjuvant inhaled gases (the trials by Greif [13], Pryor [15], Belda [12], Mayzler [14] and Myles [42]). The low-bias heterogeneity adjusted information size (LBHIS) is 4500 based on a relative risk reduction (RRR) suggested by the low-bias trials of 33% and a meta-analytic estimate of the frequency of surgical site infection in the control group (30% oxygen) on 14% with a type I error risk of 5% and a power of 80%. No crossing of the trial sequential monitoring boundary at any time despite P < 0.05 after the first trial [13]. The gap of information to reject an intervention effect of 33% relative risk reduction is approximately 1500 patients.