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Objective: This study evaluates the effects of mechanical bowel preparation (MBP) on anastomosis below the peritoneal verge and questions the influence of MBP on anastomotic leakage in combination with a diverting ileostomy in lower colorectal surgery., Summary Background Data: In a previous large multicenter randomized controlled trial MBP has shown to have no influence on the incidence of anastomotic leakage in overall colorectal surgery. The role of MBP in lower colorectal surgery with or without a diverting ileostomy remains unclear., Methods: This study is a subgroup analysis of a prior multicenter (13 hospitals) randomized trial comparing clinical outcome of MBP versus no MBP. Primary end point was the occurrence of anastomotic leakage and secondary endpoints were septic complications and mortality., Results: Total of 449 Patients underwent a low anterior resection with a primary anastomosis below the peritoneal verge. The incidence of anastomotic leakage was 7.6% for patients who received MBP and 6.6% for patients who did not. Significant risk factors for anastomotic leakage were the American Society of Anesthesiologists-classification (P = 0.005) and male gender (P = 0.007). Of total, 48 patients received a diverting ileostomy during initial surgery; 27 patients received MBP and 21 patients did not. There were no significant differences regarding septic complications and mortality between both groups., Conclusion: MBP has no influence on the incidence of anastomotic leakage in low colorectal surgery. Furthermore, omitting MBP in combination with a diverting ileostomy has no influence on the incidence of anastomotic leakage, septic complications, and mortality rate.

The impact of three current types of preoperative large bowel preparation on the microbial flora and the colonization resistance (CR) was investigated in 15 volunteers. In the first group a whole gut irrigation was performed without administration of antibiotics (group WGI). In the second group 0.5 g/l metronidazole and 1 g/l neomycin was added to the irrigation fluid (group WGI + AB). A whole gut irrigation with prior oral administration of 1 l mannitol 10% was performed in the third group. The antibiotic prophylaxis in this group consisted of two doses of 80 mg gentamicin i.v. and 500 mg metronidazole orally 24 h after lavage (group Mann + AB). One hour after the mechanical cleansing procedure was finished all volunteers were orally contaminated with one dose of an Escherichia coli test strain. The aerobic faecal reduction due to the cleansing procedure was 2-3 logs, while for the anaerobes it was 4-5 logs. The anaerobic flora in group WGI recovered within 24 h, while the aerobes showed a transient 'overgrowth' for the period of 2 days. The overgrowth of aerobes in group WGI + AB was observed for more than a week and the total numbers of aerobes started gradually to decline after the anaerobic flora had reached pretreatment levels at day three or four. Despite the normal numbers of anaerobes present 24 h after treatment, overgrowth of E. coli was seen in the group Mann + AB, probably due to residual mannitol left in the intestinal tract. The test strain of E. coli was excreted for a period of 1 week by the volunteers in the groups WGI and Mann + AB, but it was isolated for more than 10 weeks in the group WGI + AB. It is thought that all three methods of preoperative large bowel preparation decreased the CR of the gastrointestinal tract because of a disturbance of the interaction between aerobic and anaerobic microorganisms and alterations of the colonic wall. The anaerobic microflora, however, appeared to be primarily responsible for the maintenance of the CR. Antimicrobial prophylaxis should consist of a high dose, short term, systemic antibiotic regimen, not only because an adequate serum level of an appropriate drug at the time of operation substantially decreases the incidence of postoperative septic complications but also because a systemic regimen scarcely influences the CR of the gastrointestinal tract. beta-Aspartylglycine appeared to be a specific but not very sensitive marker for decreased CR.

In a prospective randomized trial, systemic antimicrobial prophylaxis with metronidazole and gentamicin was compared to the administration of metronidazole alone in elective colorectal surgery. In both groups, an identical mechanical large-bowel preparation was performed. In order to reduce the duration of the whole-gut irrigation, a 10% mannitol solution was administered before the irrigation procedure. Although no serious infections were observed in either group, the incidence of superficial wound infections was relatively high: 19% in the group with metronidazole and gentamicin prophylaxis and 25% in the other group. From all these wounds E. coli was isolated, and no obligate anaerobic bacteria were cultured. This high rate of wound infections is most likely caused by an overgrowth of E. coli after irrigation, due to the residues of mannitol in the colon, which serve as a nutrient for E. coli. It is concluded that mannitol should not be used in the preoperative mechanical preparation of the large bowel before elective colorectal surgery.