Bowel preparation did not reduce surgical site infections


In recent decades, patients in Europe coming in for colectomies, or surgical procedures targeted at the colon, have not been routinely subjected to what is known as bowel preparation, where the bowel is emptied before the operation.

In the United States , on the other hand, cleansing the bowel is relatively common.

Several extensive retrospective studies conducted in the United States were published a few years ago, indicating that bowel preparation combined with the preoperative oral administration of antibiotics appeared to significantly reduce surgical site infections.

Based on these results, American surgical associations ended up recommending bowel preparation before colectomies.

In Finland, the attitude to this practice has so far remained somewhat reserved due to the absence of randomised studies.

Bowel preparation is a stressful procedure for the patient, so conducting it is only justified when it genuinely benefits the patient. However, not a single randomised follow-up study had been conducted on the topic, so we decided to carry one out ourselves,” says Dr. Laura Koskenvuo, gastrointestinal surgeon and Ph.D. at the Helsinki University Hospital.

The study, published in the distinguished journal The Lancet, was carried out at the Helsinki and Oulu University Hospitals, as well as the Central Finland and Seinäjoki Central Hospitals.

A total of 400 patients awaiting colectomy took part in the study, half of whom were randomised into a preparation group which was given orally administered antibiotics combined with bowel cleansing with a drinkable cleansing liquid and the other half into a group in which no such preparations were made.

“According to our findings, there were no differences in treatment outcomes between the groups.

Bowel preparation did not reduce surgical site infections or the total number or severity of surgical complications. Neither was there any difference in the number of days spent at the hospital,” notes Dr. Ville Sallinen, gastrointestinal surgeon and adjunct professor at the Helsinki University Hospital.

Mechanical Bowel Preparation

Mechanical bowel preparation before elective colorectal resection remains a common practice among general and colorectal surgeons.

However, its use over the past decade has been decreasing, primarily in response to many RCTs and meta-analyses that have not only failed to show a benefit to mechanical bowel preparation but also have demonstrated an increase in complications following bowel preparation.

Two of the earliest RCTs to examine this issue were performed in 1994 by Burke et al. and Santos et al.12,13 In both of these studies the authors concluded that bowel preparation does not influence outcome after elective colorectal surgery. Since that time, continued controversy over the use of bowel preparation has spawned several more RCTs.

In 2007 Pena-Soria et al. examined the relationship between bowel preparation and surgical-site infection and anastomotic leak in 97 patients.14 

They found no difference in surgical site infection between the two groups, but a higher rate of anastomotic dehiscence in the nonprepped group (8.3% vs. 4.1%; P = .05).

The largest RCT examining this question was published in 2007 by Contant et al. and included more than 1400 patients at 13 hospitals.15 Patients were consented to receive either no bowel preparation, which included a regular diet the day before surgery versus a bowel preparation of either polyethylene glycol or sodium phosphate and a clear liquid diet the day before surgery. In this study the rate of anastomotic leak, 4.8% in patients who received bowel prep and 5.4% in patients who did not, did not differ significantly between groups (P = .69).

Patients who had mechanical bowel preparation did have fewer abscesses after anastomotic leak than those who did not (0.3% vs. 2.5%; P = .001). Other complications, such as fascial dehiscence, superficial infection, and mortality, did not differ between groups.

These authors concluded that mechanical bowel preparation before elective colorectal surgery can safely be abandoned. Several studies supported these conclusions for left-sided colon and rectal resections as well.16,17

Further buttressing the argument against mechanical bowel prep were multiple large meta-analyses synthesizing the results from the almost 20 years of trials examining this issue.

In 2004, Slim et al. analyzed the results of seven randomized trials, including 1454 patients, comparing bowel preparation with no preparation in colorectal surgery.18 They reported significantly higher rates of anastomotic leak after bowel preparation (5.6% vs. 3.2%; P = .032).

All other end points (wound infection, other septic complications, and nonseptic complications) also favored the no-preparation regimen.

In 2010 Zhu et al. specifically analyzed five RCTs that compared mechanical bowel preparation with polyethylene glycol with no preparation.19 

They found no significant differences in rates of surgical site infection, organ/space infection, mortality, or anastomotic leak between the groups. Finally, the largest and most thorough meta-analysis was published by Guenaga et al.

in 2009.17These authors analyzed 13 RCTs, including 4777 patients, comparing bowel preparation with no bowel preparation. They found that rates of anastomotic leakage, although slightly higher in the bowel preparation groups, were not significantly different following either low anterior rectal resections or colonic resections.

Rates of secondary complications, such as wound infection and extraabdominal complications, were not different between the two groups. They concluded that there was no statistically significant evidence that patients benefit from mechanical bowel preparation.

Based on this robust body of evidence, many surgeons began to reduce their use of bowel preparation prior to colorectal surgery.

However, interestingly, new evidence is emerging that mechanical bowel preparation with oral antibiotic administration is beneficial prior to elective colorectal surgery. In almost all of the trials mentioned previously, oral antibiotics were not included as part of the mechanical bowel preparation pathway.

Many investigators believe that the benefit from bowel preparation stems from the delivery of the oral antibiotics to the colon lumen and mucosa, a process that is enhanced by the mechanical colon cleanse.

In light of these concerns regarding the existing bowel preparation literature, a new series of studies have been published evaluating the efficacy of bowel preparations that include oral antibiotics.

The results of these studies, which are discussed in more detail later, indicate that, although mechanical preparation alone may not be of benefit, mechanical preparation with oral antibiotics is beneficial in reducing surgical site infection and anastomotic leak following colorectal surgery.

In 2012 Cannon et al. evaluated almost 10,000 patients undergoing elective colorectal surgery within the Veterans Administration Health System.20 They compared patients receiving no bowel prep to those receiving mechanical-only bowel prep, mechanical bowel prep plus oral antibiotics, or oral antibiotics alone.

They reported that oral antibiotics plus mechanical bowel preparation was associated with a 57% decrease in surgical site infection occurrence compared with no bowel prep (OR = 0.43; 95% CI, 0.34 to 0.55).

Following that study, in 2013 Toneva et al. reported on the association between oral antibiotic bowel preparation and length of stay and readmissions in a similar Veterans Administration Health System cohort of 8140 patients.21 They report that oral antibiotic bowel preparation was associated with a significantly reduced length of stay, as well as a significant reduction in the number of readmissions, due mostly to a reduction in readmission for infection.

In 2014 Kim et al. used the Michigan Surgical Quality Collaborative data to examine almost 1000 pairs of patients undergoing elective colectomy who differed only by administration of bowel preparation.22 

The bowel preparation group received mechanical bowel preparation with nonabsorbable oral antibiotics, and the control group received no bowel prep. These authors found that patients receiving full preparation were less likely to have any surgical site infection (5.0% vs. 9.7%; P = .0001), organ/space infection (1.6% vs. 3.1%; P = .024), and superficial surgical site infection (3.0% vs. 6.0%; P = .001). They were also less likely to develop postoperative Clostridium difficile colitis (0.5% vs. 1.8%; P = .01).

In 2015 four retrospective studies using American College of Surgeons National Surgical Quality Improvement Program–targeted colectomy data were published.23–26 Moghadamyeghaneh et al. reported on just more than 5000 patients undergoing elective colorectal resections between 2012–2013.23 

They reported no difference in postoperative morbidity between patients receiving no preparation and either mechanical preparation alone or oral antibiotic preparation alone. Multivariable analysis revealed that the combination of oral antibiotics and mechanical bowel preparation significantly reduced the risk of overall morbidity (OR = 0.63; P < .01), surgical site infection (OR = 0.31; P < .01), and anastomotic disruption (OR = 0.44; P < .01), especially following left-sided resections.

Morris et al. examined 8145 patients undergoing elective colon and rectal resections.24 They found that patients receiving oral antibiotics had a significantly lower risk of surgical site infection than either those patients receiving no bowel preparation or those receiving mechanical preparation only.

This was consistent for both open and minimally invasive approaches and for both colon and rectal resections. Scarborough et al. reported on the outcome of almost 5000 patients undergoing elective colorectal resections.25

Again, they found that patients receiving oral antibiotics combined with mechanical preparation had the lowest rate of surgical site infection, anastomotic leak, and procedure-related readmission. There was no difference noted among the no preparation, oral antibiotic alone preparation, or mechanical preparation alone groups. Finally, Kiran et al. reported on 8442 patients undergoing elective colorectal procedures.26 

After their multivariable analysis, mechanical bowel preparation with oral antibiotics was independently associated with reduced surgical site infection (OR = 0.40; 95% CI, 0.31 to 0.53), anastomotic leak (OR = 0.57; 95% CI, 0.35 to 0.94), and ileus (OR = 0.71, 95% CI, 0.56 to 0.90).

All of these studies have countered the increasingly held belief that bowel preparation prior to elective colorectal surgery is not necessary and may be harmful.

Each of these provides retrospective evidence that oral antibiotic administration in combination with a mechanical bowel preparation can have significant beneficial effects for colorectal surgery patients, including decreased risks of wound infection, anastomotic leak, ileus, and readmission. Based on this body of evidence, many providers are routinely using the combination of oral antibiotics and mechanical bowel preparation for their colorectal surgery patients.

Randomized controlled data would add to this ample body of retrospective data as the debate around the appropriate use of preoperative bowel preparation continues to evolve.


Benefits of Bowel Preparation Beyond Surgical Site Infection: A Retrospective Study


To examine whether the administration of mechanical bowel preparation (MBP) plus oral antibiotic bowel preparation (OABP) was associated with reduced surgical site infections (SSIs), which in turn leads to a reduction of non-SSI-related postoperative complications.


Administration of MBP/OABP before elective colectomy reduces the incidence of SSI. We hypothesized that reduction of SSI is on causal pathway between the use of MBP/OABP and the reduction of other postoperative complications.


The study population consisted of all colectomy cases in the American College of Surgeons National Surgical Quality Improvement Program Colectomy Targeted Participant Use Data File for 2012 and 2013. Postoperative outcomes were compared based on the type of bowel preparation: none, MBP only, OABP only, and MBP plus OABP adjusting for other covariates.


The cohort included 19,686 patients. Of these 5060 (25.7%) patients did not receive any form of bowel preparation, 8020 (40.7%) received MBP only, 641 (3.3%) received OABP only, and 5965 (30.3%) received MBP plus OABP. Patients who received MBP plus OABP had a lower incidence of superficial SSI, deep SSI, organ space SSI, any SSI, anastomotic leak, postoperative ileus, sepsis, readmission, and reoperation compared with patients who received neither (all P < 0.01). The reduction in SSI incidence was associated with a reduction in wound dehiscence, anastomotic leak, pneumonia, prolonged requirement of mechanical ventilator, sepsis, septic shock, readmission, and reoperation.


Combined MBP plus OABP before elective colectomy was associated with reduced SSI, which ultimately was associated with a reduction in non-SSI-related complications.PMID: 26727098 DOI: 10.1097/SLA.0000000000001576

More information: Laura Koskenvuo et al, Mechanical and oral antibiotic bowel preparation versus no bowel preparation for elective colectomy (MOBILE): a multicentre, randomised, parallel, single-blinded trial, The Lancet (2019). DOI: 10.1016/S0140-6736(19)31269-3

Journal information: The Lancet
Provided by University of Helsinki


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