- A combined mechanical (using laxatives) and oral antibiotic bowel preparation probably reduces the occurrence of infections of the surgical site (wound infections and infections in the abdominal cavity) as well as the likelihood of anastomotic leakage (leakage of the suture connection of the bowel) compared with mechanical bowel preparation alone.
- Oral antibiotics alone might be as effective as a combined mechanical and oral antibiotic bowel preparation, but this cannot be clearly determined based on the available data.
- Whether no bowel preparation compared with a combined mechanical and oral antibiotic bowel preparation has an influence on the occurrence of postoperative complications could not be determined on the basis of the available data.
What is the purpose of preoperative bowel preparation?
Due to the naturally bacterial colonisation of the large bowel, infections of the surgical site are more frequent after operations in which the large bowel is opened. To prevent these infections, bowel preparation before surgery is intended to reduce faecal contamination of the bowel and minimise bacterial colonisation.
How is the bowel preparation done?
Preoperative bowel preparation can be done mechanically, using laxatives to rinse the bowel, or by taking oral antibiotics that lead to local decontamination. These two methods can be performed either alone or in combination.
What did we want to find out?
We wanted to find out whether combined mechanical and oral antibiotic bowel preparation compared with mechanical or oral antibiotic preparation alone or no bowel preparation has an effect on:
- the occurrence of surgical site infections
- the occurrence of anastomotic leakages
In addition, we wanted to find out whether combined bowel preparation had an effect on mortality, the occurrence of mild or severe postoperative complications, the likelihood of postoperative ileus (bowel motility disorder) or the length of hospital stay. Furthermore, we wanted to investigate whether side effects of the bowel preparation interventions differ between combination therapy and sole mechanical, sole oral antibiotic, or no bowel preparation.
What did we do?
We searched for studies comparing combined mechanical and oral antibiotic bowel preparation with sole mechanical, sole oral antibiotic, or no bowel preparation in patients scheduled for colon or rectal resection.
We compared and summarised the results of the studies and rated our confidence in the evidence, based on factors such as study methods and sizes.
What did we find?
We included 21 studies in which patients scheduled for colon or rectal resection were assigned either to a group receiving combined mechanical and oral antibiotic bowel preparation or to a comparison group. The comparison group received mechanical bowel preparation alone in 17 studies, oral antibiotics alone in three studies, and no bowel preparation at all in one study. All participants received intravenous antibiotic prophylaxis during surgery. The studies included a total of 5968 participants, of whom 5264 were analysed.
Most of the studies were conducted in industrialised countries in Europe or Asia. Bowel preparation was conducted over one to three days before surgery and the follow-up period was 30 days in most of the studies. No industrial funding was reported by any of the studies, but only five of the 21 studies provided information on their funding.
Overall, slightly more men (58%) than women (42%) were included. The average age of the study participants varied between 42 and 69 years.
We found moderate-certainty evidence that combined mechanical and oral antibiotic bowel preparation probably reduces the risk of surgical site infections and leakages without affecting mortality, the occurrence of postoperative ileus or length of hospital stay.
When comparing combined bowel preparation with oral antibiotics alone or with no bowel preparation, we found low-certainty evidence that there is little to no difference between the compared approaches.
What are the limitations of the evidence?
There are different reasons why our confidence in the evidence is limited.
We are moderately confident in the evidence regarding the reduction of surgical site infections through combined mechanical and oral antibiotic bowel preparation, because different surgical strategies (in terms of surgical access and type and location of bowel resection) and also different methods of bowel preparation (in terms of agent, dose and timing) were used. We are also only moderately confident in the reduction of anastomotic leakage through combined mechanical and oral antibiotic bowel preparation, because just a few cases occurred across the included studies.
Regarding the comparison of combination therapy with oral antibiotics alone, we have little confidence in the evidence because not enough studies examined this issue to be certain about the results of our outcomes. In addition, there are some concerns about the methods used in the included studies.
As there is only one study, we also have little confidence in the evidence comparing combined bowel preparation with no bowel preparation.
How up to date is this evidence?
This evidence is up-to-date as of December 2021.
Based on moderate-certainty evidence, our results suggest that MBP+oAB is probably more effective than MBP alone in preventing postoperative complications. In particular, with respect to our primary outcomes, SSI and anastomotic leakage, a lower incidence was demonstrated using MBP+oAB. Whether oAB alone is actually equivalent to MBP+oAB, or leads to a reduction or increase in the risk of postoperative complications, cannot be clarified in light of the low- to very low-certainty evidence. Similarly, it remains unclear whether omitting preoperative bowel preparation leads to an increase in the risk of postoperative complications due to limited evidence.
Additional RCTs, particularly on the comparisons of MBP+oAB versus oAB alone or nBP, are needed to assess the impact of oAB alone or nBP compared with MBP+oAB on postoperative complications and to improve confidence in the estimated effect. In addition, RCTs focusing on subgroups (e.g. in relation to type and location of colon resections) or reporting side effects of the intervention are needed to determine the most effective approach of preoperative bowel preparation.
The success of elective colorectal surgery is mainly influenced by the surgical procedure and postoperative complications. The most serious complications include anastomotic leakages and surgical site infections (SSI)s, which can lead to prolonged recovery with impaired long-term health.
Compared with other abdominal procedures, colorectal resections have an increased risk of adverse events due to the physiological bacterial colonisation of the large bowel. Preoperative bowel preparation is used to remove faeces from the bowel lumen and reduce bacterial colonisation. This bowel preparation can be performed mechanically and/or with oral antibiotics. While mechanical bowel preparation alone is not beneficial, the benefits and harms of combined mechanical and oral antibiotic bowel preparation is still unclear.
To assess the evidence for the use of combined mechanical and oral antibiotic bowel preparation for preventing complications in elective colorectal surgery.
We searched MEDLINE, Embase, CENTRAL and trial registries on 15 December 2021.
In addition, we searched reference lists and contacted colorectal surgery organisations.
We included randomised controlled trials (RCTs) of adult participants undergoing elective colorectal surgery comparing combined mechanical and oral antibiotic bowel preparation (MBP+oAB) with either MBP alone, oAB alone, or no bowel preparation (nBP). We excluded studies in which no perioperative intravenous antibiotic prophylaxis was given.
We used standard methodological procedures as recommended by Cochrane. Pooled results were reported as mean difference (MD) or risk ratio (RR) and 95 % confidence intervals (CIs) using the Mantel-Haenszel method. The certainty of the evidence was assessed with GRADE.
We included 21 RCTs analysing 5264 participants who underwent elective colorectal surgery.
None of the included studies had a high risk of bias, but two-thirds of the included studies raised some concerns. This was mainly due to the lack of a predefined analysis plan or missing information about the randomisation process.
Most included studies investigated both colon and rectal resections due to malignant and benign surgical indications. For MBP as well as oAB, the included studies used different regimens in terms of agent(s), dosage and timing.
Data for all predefined outcomes could be extracted from the included studies. However, only four studies reported on side effects of bowel preparation, and none recorded the occurrence of adverse effects such as dehydration, electrolyte imbalances or the need to discontinue the intervention due to side effects.
Seventeen trials compared MBP+oAB with sole MBP.
The incidence of SSI could be reduced through MBP+oAB by 44% (RR 0.56, 95% CI 0.42 to 0.74; 3917 participants from 16 studies; moderate‐certainty evidence) and the risk of anastomotic leakage could be reduced by 40% (RR 0.60, 95% CI 0.36 to 0.99; 2356 participants from 10 studies; moderate‐certainty evidence). No difference between the two comparison groups was found with regard to mortality (RR 0.87, 95% CI 0.27 to 2.82; 639 participants from 3 studies; moderate‐certainty evidence), the incidence of postoperative ileus (RR 0.89, 95% CI 0.59 to 1.32; 2013 participants from 6 studies, low‐certainty of evidence) and length of hospital stay (MD -0.19, 95% CI -1.81 to 1.44; 621 participants from 3 studies; moderate‐certainty evidence).
Three trials compared MBP+oAB with sole oAB.
No difference was demonstrated between the two treatment alternatives in terms of SSI (RR 0.87, 95% CI 0.34 to 2.21; 960 participants from 3 studies; very low‐certainty evidence), anastomotic leakage (RR 0.84, 95% CI 0.21 to 3.45; 960 participants from 3 studies; low‐certainty evidence), mortality (RR 1.02, 95% CI 0.30 to 3.50; 709 participants from 2 studies; low‐certainty evidence), incidence of postoperative ileus (RR 1.25, 95% CI 0.68 to 2.33; 709 participants from 2 studies; low‐certainty evidence) or length of hospital stay (MD 0.1 respectively 0.2, 95% CI -0.68 to 1.08; data from 2 studies; moderate‐certainty evidence).
One trial (396 participants) compared MBP+oAB versus nBP. The evidence is uncertain about the effect of MBP+oAB on the incidence of SSI as well as mortality (RR 0.63, 95% CI 0.33 to 1.23 respectively RR 0.20, 95% CI 0.01 to 4.22; low‐certainty evidence), while no effect on the risk of anastomotic leakages (RR 0.89, 95% CI 0.33 to 2.42; low‐certainty evidence), the incidence of postoperative ileus (RR 1.18, 95% CI 0.77 to 1.81; low‐certainty evidence) or the length of hospital stay (MD 0.1, 95% CI -0.8 to 1; low‐certainty evidence) could be demonstrated.