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Oral mechanical bowel preparation (OMBP) is often prescribed preoperatively for patients undergoing elective colorectal surgery.
We conducted a systematic review to summarize the evidence on the comparative effectiveness (prevention of surgical complications) and safety (harms) of OMBP versus no preparation, OMBP versus enema only, and among different OMBP strategies.
We searched MEDLINE®, the Cochrane Central Register of Controlled Trials, EMBASE™, and CINAHL® without any language restriction (last search on September 6, 2013). We also searched the U.S. Food and Drug Administration Web site (last search on May 17, 2013). We supplemented searches by asking technical experts and perusing reference lists for additional citations.
Study eligibility criteria, participants, and interventions
We included English-language full-text reports of randomized controlled trials (RCTs; ≥10 patients per arm), and nonrandomized comparative studies (NRCSs; ≥100 patients per arm) of OMBP strategies in adults or children undergoing elective colon or rectal surgery. For harms we also included cohort studies of %ge;200 participants. Eligible comparative studies reported on predetermined clinical outcomes, including overall mortality, infectious outcomes, anastomotic leakage; health system and resource utilization outcomes such as readmissions after surgery or length of stay; and patient-centered outcomes such as patient satisfaction and quality of life.
Study appraisal and synthesis methods
A single investigator extracted data from each study; a second investigator verified quantitative results and intervention descriptions. We assessed the risk of bias for each outcome and the strength of the evidence following the processes described in the Agency for Healthcare Research and Quality "Methods Guide for Effectiveness and Comparative Effectiveness Reviews." We synthesized results qualitatively, and performed Bayesian pairwise and network meta-analyses. Models accounted for between-study heterogeneity.
Sixty unique studies (in 65 publications) were included: 44 RCTs, 10 NRCSs, and 6 single-group cohorts; 58 studies were included in main analyses (1 retracted publication and 1 possible duplicate were excluded). Of those, 18 RCTs were included in meta-analyses comparing OMBP versus enema or no preparation for the following outcomes: overall mortality, anastomotic leakage, wound infection, peritonitis, surgical site infection, and reoperation. Credible intervals of the summary odds ratio included the null value of 1.0 (no difference) for comparisons of OMBP versus no preparation or enema for all outcomes. When comparing OMBP to no preparation, credible intervals did not exclude modest (e.g., 30-50%) effects on overall mortality, anastomotic leakage, wound infection, or peritonitis in either direction. For all other comparisons, credible intervals did not exclude even larger effects. Results were robust to extensive sensitivity analyses. Twenty-four RCTs comparing alternative active OMBP strategies (including 1 RCT comparing inpatient vs. outpatient preparation) assessed highly diverse outcomes and most pertained to interventions that are no longer in clinical use. Evidence on the adverse events of OMBP was too poorly reported to allow definitive conclusions.
The evidence regarding OMBP for colorectal surgery is limited in the following ways: (1) most studies enrolled small numbers of patients and reported low event rates for major clinical events; (2) studies provided limited or no information for important clinical subgroups, particularly those defined by anatomic location of surgery (colon vs. rectal surgery) and the type of surgical procedure performed (e.g., open vs. laparoscopic surgery); (3) studies comparing alternative active OMBP strategies used a large number of diverse preparation regimes and reported results for heterogeneous, often poorly defined, outcomes; (4) nonrandomized trials, and particularly observational studies, could not effectively supplement the results of randomized trials because of shortcomings in their design and analysis (e.g., diversity of outcomes and suboptimal confounding control).
We found weak evidence suggesting that OMBP has similar effectiveness as no preparation with respect to all-cause mortality, anastomotic leakage, wound infection, and peritonitis for patients undergoing elective colorectal surgery. However, the evidence base was too weak to confidently exclude either modest benefit or modest harm. Evidence for other outcomes and comparisons was insufficient to draw definitive conclusions. The effectiveness of alternative active OMBP strategies could not be assessed because the studies compared interventions that are no longer used. Data on harms were also too sparse for analysis. Therefore, there is a clear need for new comparative studies (both randomized and nonrandomized) of the currently used OMBP strategies.
The PROSPERO registration number of the protocol of this review is CRD42013004381.