Effectiveness of mechanical bowel preparation versus no preparation on anastomotic leakage in colorectal surgery: a systematic review and meta-analysis.

It has been a standard practice to perform mechanical bowel preparation (MBP) prior to colorectal surgery to reduce the risk of colorectal anastomotic leakages (CAL). The latest Cochrane systematic review suggests there is no benefit for MBP in terms of decreasing CAL, but new studies have been published. The aim of this systematic review and meta-analysis is to update current evidence for the effectiveness of preoperative MBP on CAL in patients undergoing colorectal surgery. Consequently, PubMed, MEDLINE, Embase, CENTRAL and CINAHL were searched from 2010 to March 2017 for randomised controlled trials (RCT) that compared the effects of MBP in colorectal surgery on anastomotic leakages. The outcome CAL was expressed in odds ratios and analysed with a fixed-effects analysis in a meta-analysis. Quality assessment was performed by the cochrane risk of bias tool and grades of recommendation, assessment, development and evaluation (GRADE) methodology. Eight studies (1065 patients) were included. The pooled odds ratio showed no significant difference of MBP in colorectal surgery on CAL (odds ratio (OR) = 1.15, 95% CI = 0.68-1.94). According to GRADE methodology, the quality of the evidence was low. To conclude, MBP for colorectal surgery does not lower the risk of CAL. These results should, however, be interpreted with caution due to the small sample sizes and poor quality. Moreover, the usefulness of MBP in rectal surgery is not clear due to the lack of stratification in many studies. Future research should focus on high-quality, adequately powered RCTs in elective rectal surgery to determine the possible effects of MBP.