Background: Mechanical bowel preparation is a common practice before elective colorectal surgery. We aimed to compare the rate of anastomotic leakage after elective colorectal resections and primary anastomoses between patients who did or did not have mechanical bowel preparation.
Methods: We did a multicentre randomised non-inferiority study at 13 hospitals. We randomly assigned 1431 patients who were going to have elective colorectal surgery to either receive mechanical bowel preparation or not. Patients who did not have mechanical bowel preparation had a normal meal on the day before the operation. Those who did were given a fluid diet, and mechanical bowel preparation with either polyethylene glycol or sodium phosphate. The primary endpoint was anastomotic leakage, and the study was designed to test the hypothesis that patients who are given mechanical bowel preparation before colorectal surgery do not have a lower risk of anastomotic leakage than those who are not. The median follow-up was 24 days (IQR 17-34). We analysed patients who were treated as per protocol. This study is registered with ClinicalTrials.gov, number NCT00288496.
Findings: 77 patients were excluded: 46 who did not have a bowel resection; 21 because of missing outcome data; and 10 who withdrew, cancelled, or were excluded for other reasons. The rate of anastomotic leakage did not differ between both groups: 32/670 (4.8%) patients who had mechanical bowel preparation and 37/684 (5.4%) in those who did not (difference 0.6%, 95% CI -1.7% to 2.9%, p=0.69). Patients who had mechanical bowel preparation had fewer abscesses after anastomotic leakage than those who did not (2/670 [0.3%] vs 17/684 [2.5%], p=0.001). Other septic complications, fascia dehiscence, and mortality did not differ between groups.
Interpretation: We advise that mechanical bowel preparation before elective colorectal surgery can safely be abandoned.