Fig. 4

Trial sequential analysis plot of postoperative duration of mechanical ventilation (overall cohort). Trial sequential analysis of 11 RCTs that compared RIPreC versus control on postoperative duration of mechanical ventilation. The cumulative z curve did not cross the conventional boundary. The information size was too small to produce the inner wedge futility area, indicating the current evidence is inconclusive. A required information size of 8,174 patients was calculated using α = 0.05 (two sided), β = 0.20 (power 80%) and the mean difference generated in the conventional meta-analysis