The practice of MBP then spread from colorectal surgery to other areas of general and gynecologic surgery without clear evidence from randomized trials that it was necessary or beneficial.8 As surgical techniques improved over the ensuing decades, and antibiotics evolved, mortality and SSI rates dropped—although it is unclear whether this drop in infection is attributable to MBP.1
In the 1990s, researchers began to question the value of MBP in surgical practice. Multiple randomized, controlled trials in the colorectal literature have demonstrated that MBP does not reduce the rate of incisional or deep SSI, compared with no bowel preparation.9-11 The populations studied in these trials were undergoing planned bowel resection and primary re-anastomosis— procedures known to elevate the risk of contamination, unlike the majority of gynecologic surgical procedures. Even in this higher-risk population, however, MBP failed to reduce the risk of SSI, suggesting that, in less contaminated surgeries, it would have even fewer benefits.
In its practice bulletin on antibiotic prophylaxis from 2009, the American Congress of Obstetricians and Gynecologists (ACOG) noted: “There is no evidence that mechanical bowel preparation further reduces infection risk” beyond the reduction achieved with routine use of perioperative antibiotics.12
Preventing anastomotic leakage
Investigators have suggested that MBP reduces the risk of anastomotic leaks of the colon by decreasing contamination at the suture site.13 A close review of the colorectal literature, however, reveals that MBP does not affect anastomotic leakage in patients who undergo planned colon resection and primary re-anastomosis.9,10,14-17
A 2011 Cochrane review that included 5,805 patients undergoing elective colon and rectal surgery confirmed that neither oral nor rectal MBP was associated with any benefit in terms of the rates of anastomotic leakage and SSI.10 Some randomized studies have found nonstatistically significant reductions in the anastomotic leakage rate in patients who did not undergo MBP—a finding attributed to the lack of denuded mucosa and inflammation in the unprepared colon.9,15,18
However, one large, randomized, clinical trial of more than 1,000 patients found that, when anastomotic leakage did occur, the risk of infection was greater among patients who had not undergone MBP.19
Reducing the rates of intraoperative contamination and colon injury
Planned resection and inadvertent colon injury both have the potential to contaminate the surgical field, increasing the risk of morbidity. Surgeons have turned to MBP to minimize this risk in the planned surgical setting, although the practice does not appear to reduce infection or the risk of subsequent anastomotic leakage. It is largely unknown how bowel preparation affects bowel spillage during colon resection. Most investigators empirically believe that MBP will reduce bowel spillage during planned colon resection in an uncontaminated field,13 although one prospective study suggested a trend toward increased spillage of bowel contents and intraoperative contamination in patients who had undergone MBP.20
In gynecologic surgery for benign conditions, colon resection is generally unplanned, usually the result of inadvertent colon injury or unexpected findings. Traditional teaching has been that, if an unprepared colon becomes injured, the patient requires a colostomy rather than primary anastomosis, simply because there are bowel contents contaminating the surgical field.
Gynecologists may be hesitant to challenge this practice because the choice of primary anastomosis versus colostomy is often made by the consulting general surgeon. Given the low risk of bowel injury (estimated to be <2% in gynecologic surgery) and emerging data on fecal contamination and bowel resection in the trauma literature, MBP may be unnecessary on a population-wide basis.21
In fact, the trauma literature might be instructive in understanding how inadvertent colon injury in gynecologic surgery should be managed, regardless of the patient’s bowel-preparation status. Multiple randomized, controlled trials of colostomy versus primary anastomosis in trauma patients who had penetrating colon injuries demonstrated no difference in the rates of mortality and complications, including SSI and anastomotic leakage.22-24 Both colorectal and trauma surgeons performed planned and unplanned colectomy and primary re-anastomosis without MBP.
Based on these data, the recommended practice in trauma surgery is primary repair of the colon, confirming that the unprepared colon can be safely re-anastomosed, even in a grossly contaminated field. Extrapolating from this literature, it stands to reason that colon injury at the time of gynecologic surgery without preoperative MBP could also be managed primarily, eliminating the impetus for gynecologists to use MBP to avoid bowel diversion.
Although evidence-based practice is highly recommended, it is important to recognize that it is beyond the scope of most general gynecologists to perform bowel resection and anastomoses in the event of inadvertent bowel injury. Gynecologic surgeons must know the practice patterns of their local institution; if the general surgeons in that institution do not follow current recommendations, it may be prudent to continue to use MBP in cases that carry a high risk of bowel injury to avoid a potential colostomy.