The influence of a dominating centre on a quantitative systematic review of granisetron for preventing postoperative nausea and vomiting

Background: We performed a meta-analysis on granisetron in the prevention o f postoperative nausea and vomiting (PONV) and further investigated whether total results and the dose-response characteristics may be significantly a ffected by a single centre. Methods: Systematically searched randomised controlled trials (RCT) using g ranisetron for the prevention of PONV after general anaesthesia were includ ed in the analysis. The pooled relative risks (RR) and numbers needed to tr eat (NNT) with their corresponding 95%-confidence intervals C(I) were calcu lated. For all centres, one dominating centre and other centres pooled, com parisons were performed according to all doses, low dose (less than or equa l to 20 mug/kg) and high dose (> 20 mug/kg) granisetron. Results: A total of 27 RCT with 2938 patients were included in the analysis . RR (CI) to suffer from PONV with granisetron when all comparisons were co nsidered was 0.46 (0.39-0.54), 0.7 (0.6-0.81) and 0.34 (0.28-0.41) for all doses, low and high dose, respectively RR of the dominating centre (1867 pa tients) were significantly better compared to the remaining centres (1071 p atients), with 0.41 (0.34-0.49) and 0.60 (0.49-0.73), respectively. In the dominating centre low dose granisetron was ineffective with a RR of 0.84 (0 .68-1.04), while high dose granisetron led to a strong decrease with a RR o f 0.30 (0.26-0.36). In contrast, the RR of other centres pooled for low and high dose granisetron were comparable with 0.62 (0.49-0.79) and 0.56 (0.42 -0.75), respectively. Conclusions: Overall results and dose-response characteristics of meta-anal yses may be significantly altered by one dominating centre. Further, if dat a of a dominating centre do not appear to be valid for other centres, it ma y seem advisable to either exclude them from the analysis or to perform sub -group analyses so that results without the data from the dominating centre are available.