The Role of Bowel Preparation in Colorectal Surgery

Results of the 2012-2015 ACS-NSQIP Data

Aaron L. Klinger, MD; Heather Green, MS; Dominique J. Monlezun, MD, PhD, MPH; David Beck, MD; Brian Kann, MD; Herschel D. Vargas, MD; Charles Whitlow, MD; David Margolin, MD


Annals of Surgery. 2019;269(4):671-677. 

In This Article


Our data show that compared to no preparation combined mechanical and oral antibiotic bowel preparation before colon or rectal surgery is associated with reduced odds of SSI, organ space infection, anastomotic leak, wound dehiscence, and C. difficile colitis and reduced length of stay. Likewise, when compared to either mechanical bowel prep or antibiotic bowel prep alone combined prep is associated with reduced odds of SSI.

Here we provide strong evidence that combined bowel preparation works to decrease infectious complications. Although we use powerful statistical methods in this study, a randomized controlled study would offer stronger evidence and is lacking. This study has several key strengths. It is the largest known multiyear and multisite analysis of postoperative infection and complications. It compares not only dual preparation to no preparation but also dual preparation to MBP and ABP alone. We also provide stratified analysis for colon and rectal patients, and use propensity score analysis and forward and backward regression to produce optimal final regression models. Although causative relationships between bowel preparation techniques and study endpoints are optimally tested using a randomized trial design, this study's use of such a large dataset with such advanced statistical techniques provides the closest approximation to randomized results given the latest statistical best practices. Furthermore ACS-NSQIP data are collected by trained specialists from patients treated by surgeons from multiple institutions and practice types resulting in results that are germane to all practices. To provide true causal evidence however, a randomized controlled trial would have to be performed.

The limitations of this study are important and should not be ignored. ACS-NSQIP follows patients for 30 days and any complication beyond this period will not be captured. Furthermore, although ACS-NSQIP measures many important variables, these data can be lacking for some patients and it does not record all measures. Importantly, the database does not record usage of preoperative intravenous antibiotic prophylaxis. Analysis of the Surgical Care Improvement Project suggest compliance with appropriate preoperative antibiotics is >90%.[28,29] Although this treatment has become standard of care, one cannot assume that all patients received systemic prophylaxis, that they received appropriate antibiotics, that antibiotics were given at the appropriate time, or that repeat antibiotic doses were given when indicated. Likewise many patients were excluded from analysis because of missing data. We cannot assume that these patients were otherwise the same as those patients included in the study. There is also not a standardized bowel preparation protocol for this database and there is room for variation in what preparation was provided. We do know that incomplete preparation and enemas or suppositories were counted as "no mechanical preparation." As a retrospective study, room exists for selection bias between prepped and unprepped patients. Although propensity matching theoretically controls for this potential bias, it is always possible that unmeasured factors contributed to the observed outcomes. Lastly, although we included a variety of commonly performed colorectal procedures (by CPT code), we cannot extend our findings to patients that received a diverting stoma or to other procedures not included in our analysis.

MBP before colorectal surgery, practiced for decades, was previously thought of as surgical dogma. The benefits provided by MBP were first challenged by Hughes in 1972. He reviewed his own results and compared 46 patients who received some form of mechanical preparation (no standardization) to 51 who received no preparation. He found a 15% infection rate in the prepared group and a 19% infection rate in the unprepared group. He noted that despite mechanical preparation bowel was often found to be loaded with stool intraoperatively. Based on this review he concluded that "vigorous mechanical preparation is not necessary."[30]

The value of MBP came under further scrutiny in the late 1980s and 1990s when various studies failed to find any benefit to the use of MBP alone.[31–34] The first randomized controlled study of MBP was performed by Brownson et al[35] in 1992. They compared 86 patients receiving MBP to 93 receiving no preparation. They found no improvement in rates of wound infection, intra-abdominal infection, or anastomotic leak with MBP use. A 2003 Cochrane review by Güenaga et al,[9,36–38] updated in 2005, 2009, and again in 2011 analyzed 20 studies on MBP in colorectal surgery. This review found no significant difference between surgical outcomes on prepped versus unprepped bowel and even suggested that MBP may be dangerous. A 2010 study by Eskicioglu et al[39] reviewed 14 randomized controlled trials and 8 meta-analyses. She concluded, based on these studies, that MBP should be omitted prior to elective open colectomy, a statement officially endorsed by the Canadian Society of Colon and Rectal Surgeons. More recently, Atkinson et al[10] found oral antibiotics without mechanical preparation to result in decreased rates of SSI compared to no preparation suggesting that it may be possible to omit MBP.

Others have challenged the benefit offered by oral antibiotic preparation, especially with preoperative systemic antibiotic administration becoming standard of care.[11,12] The use of preoperative oral antibiotics has also been linked to increased rates of C. difficile colitis.[13] Englesbe et al's[40] analysis of the effects of bowel preparation on 370 paired colorectal cases in Michigan found dual preparation to reduce SSI and organ space infection compared to mechanical preparation alone with no significant differences in C. difficile infection. A follow-up study of the Michigan cohort by Kim et al evaluated dual preparation to no preparation for 957 paired cases. This too showed dual preparation to have reduced incidences of infectious complications as well as a decrease in C. difficile.[41] Importantly, neither study evaluated rectal resection or the effects of ABP given without MBP.

Scarborough[42] and Kiran[43] in 2 separate studies evaluated the effects of bowel preparation using the 2012 ACS-NSQIP colon targeted database. Kiran et al found dual preparation to result in lower rates of SSIs and anastomotic leak and postoperative ileus. This study included patients with diverting stomas which have the potential to account for reduction in infectious complications and anastomotic leak rates. Furthermore, ABP alone was not evaluated.

Scarborough compared ABP, MBP, dual preparation, and no preparation. He found dual preparation to result in fewer SSIs, leaks, and readmissions than no preparation but found no significant benefit to MBP or ABP alone. Neither study evaluated Clostridium rates as this outcome was not included in the 2012 ACS-NSQIP database.

Multiple studies during the past 70 years have shown benefit to operating on mechanically cleared and antibiotic treated bowel. These benefits have been questioned more recently, however, and multiple studies dispute previously shown advantages. This camp points toward large cohort studies that find no advantage to MBP alone and question the role of oral antibiotics in an era where the vast majority of patients receive systemic intravenous antibiotics preoperatively. Furthermore, potential complications of bowel preparation including Clostridiuminfection have been noted. Despite this, preoperative bowel preparation remains popular but not universal in elective colorectal resection.

We show that while MBP alone does not offer significant advantages over no bowel preparation, ABP needs MBP to function properly. Furthermore, not only do bowel preparations not increase the rate of postoperative C. difficilecolitis, combined ABP/MBP actually results in fewer C. difficile infections. Given the strength of our data and statistical methods, we are confident in recommending combined bowel preparation, when possible, for every colorectal resection.

It is clear that combined MBP/ABP results in lower rates of infectious complications in elective colon and rectal surgery. It is still unknown what the ideal mechanical and oral antibiotic agents are. The most commonly used mechanical preparations consist of polyethylene glycol or sodium phosphate, both osmotic cathartics although other drugs exist and are used. The best studied antibiotic protocol is the Nichols/Condon neomycin and erythromycin preparation, as described in 1972 or modified to substitute metronidazole for erythromycin but a variety of other oral antibiotic preparations have been studied over the past 70 years.[2,44]