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The effect of mechanical bowel preparation on anastomotic leaks in elective left-sided colorectal resections Ahmad Elnahas, M.D., F.R.C.S.C.a, David Urbach, M.D., M.Sc., F.R.C.S.C.a, Gerald Lebovic, Ph.D.b, Muhammad Mamdani, Pharm.D., M.A., M.P.H.b, Allan Okrainec, M.D., M.H.P.E., F.R.C.S.C., F.A.C.S.a, Fayez A. Quereshy, M.D., M.B.A., F.R.C.S.C.a, Timothy D. Jackson, M.D., M.P.H., F.R.C.S.C., F.A.C.S.a,* a
Division of General Surgery, Department of Surgery, University Health Network, University of Toronto, 399 Bathurst Street, Toronto, Ontario, M5T 2S8, Canada; bApplied Health Research Centre, Keenan Research Centre, Li Ka Shing Knowledge Institute of St. Michael’s Hospital, Toronto, Ontario, Canada.
KEYWORDS: Bowel preparation; Anastomotic leaks; Colorectal surgery
Abstract BACKGROUND: Routine preoperative mechanical bowel preparation (MBP) for left-sided colorectal resections remains controversial. This study aims to evaluate the association between MBP and 30-day anastomotic leaks. METHODS: A retrospective cohort study was conducted using data from the National Surgical Quality Improvement Program from 2011 to 2012. Multiple imputation was used for missing data, and a multivariable logistic regression was performed to adjust for clinically relevant variables. A propensity score–adjusted model was performed as a sensitivity analysis. RESULTS: A total of 2,581 patients (57%) received preoperative MBP, whereas 1,935 (43%) did not. The 30-day anastomotic leak rate with and without preoperative MBP was 3.1% and 5.1%, respectively. After covariate adjustment, MBP omission was significantly associated with a 40% increased odds of 30-day anastomotic leaks (odds ratio 1.41, P 5 .04, 95% confidence interval 1.01 to 1.93). CONCLUSIONS: MBP omission was associated with a higher rate of 30-day anastomotic leaks. A large, well-designed, randomized controlled trial is needed to further evaluate this relationship. Ó 2015 Elsevier Inc. All rights reserved.
Disclaimer: American College of Surgeons’ National Surgical Quality Improvement Program (ACS NSQIP) and the hospitals participating in the ACS NSQIP are the source of the data used here; they have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors. There were no relevant financial relationships or any sources of support in the form of grants, equipment, or drugs. The authors declare no conflicts of interest. * Corresponding author. Tel.: 11-416-603-5599; fax: 11-416-603-6458 E-mail address: [email protected] Manuscript received January 21, 2015; revised manuscript March 23, 2015 0002-9610/$ - see front matter Ó 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.amjsurg.2015.03.030
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Surgeons commonly use mechanical bowel cleansing agents, such as polyethylene glycol and sodium phosphate, as a preoperative strategy to reduce postoperative infectious complications after colorectal anastomoses.1,2 Infectious wound complications, and especially anastomotic leakage, are considered major causes of morbidity after colorectal resections and can result in prolonged hospital stays.3,4 The widespread application of mechanical bowel preparation (MBP) has been attributed to its effect on decreasing intraluminal bacterial count, eliminating passage of solid feces, and improving bowel handling during construction of the anastomosis.3 As well, MBP is considered very beneficial in cases where colonic tumors are small, and performing an intraoperative colonoscopy may be necessary.5 The routine practice of MBP became controversial after several studies, including retrospective series and prospective randomized trials that demonstrated the safety and feasibility of colorectal surgery without preoperative bowel cleansing.3 Support against the use of MBP was further promoted based on better patient experience and the avoidance of side effects, such as preoperative dehydration, nausea, vomiting, and electrolyte abnormalities.5 As well, the advent of enhanced recovery programs and ‘‘fast-track’’ surgery has encouraged the practice of omitting MBP. However, with a higher risk of anastomotic leakage after left-sided colorectal resections, the routine omission of MBP in this specific subgroup warrants further evaluation.6 Additionally, MBP might offer better protection than diversion in the event of a leak by eliminating contamination from the potential column of stool above the anastomosis. Our primary study objective was to determine whether omission of MBP before elective colorectal resections with a left-sided anastomosis was associated with a higher rate of 30-day anastomotic leaks. Our secondary objective was to compare the postoperative length of stay (LOS) between groups.
44,208, 44,210, 44,145, 44,146, and 44,150. Diverting stomas (ie, ileostomy or colostomy) were identified either as part of the principal operative code (ie, 44,146 and 44,208) or a separate secondary code (ie, 44,310 and 44,320). Operations with noncolonic anastomoses (ie, ileoanal anastomoses) were excluded from the study.
Methods Study population We used data from the American College of Surgeons’ National Surgical Quality Improvement Program (ACSNSQIP) and colon-targeted participant use data files for the year 2011 and 2012 to conduct a retrospective cohort study. The ACS-NSQIP is a nationally validated, risk-adjusted database that captures 30-day clinical outcomes on patients undergoing major operations, and its methodology has been well described.7–11 Our study protocol was approved by the University Health Network Research Ethics Board. Our study population included patients who underwent an elective colorectal resection with a left-sided anastomosis in 2011 and 2012. Eligible operations included subtotal colectomies, partial left-sided resections, and low anterior resections. Operations were identified based on the following current procedural terminology codes: 44,207,
Outcomes The main outcome of our study was the 30-day anastomotic leak rate. The secondary outcome was the postoperative LOS.
Covariates We considered variables:
the
following
clinically
relevant
Demographics: Age Sex Body mass index (BMI) Current smoker within 1 year (yes/no) Functional health status (dependent/independent) Comorbidities: American Society of Anesthesiologists (ASA) classification (R3, 1 to 2) Diabetes requiring oral agents or insulin (yes/no) Renal failure (yes/no) Coronary artery disease (yes/no) Congestive heart failure (yes/no) Hypertension requiring medication (yes/no) Preoperative factors: Low-serum albumin level (,3.5 g/dL) (yes/no) Chronic steroid use greater than 10 days (yes/no) Chemotherapy within 90 days of surgery (yes/no) Radiotherapy within 90 days of surgery (yes/no) Oral antibiotic preparation (yes/no) Operative approach (laparoscopic/open) Colorectal cancer (yes/no) Inflammatory bowel disease (yes/no) Diverticular disease (yes/no) Operative factors: Operative time Intraoperative transfusion (yes/no) Enterocolic anastomosis (yes/no) Diverting stoma (yes/no)
Statistical analysis Patients satisfying the inclusion criteria were selected for analysis, and descriptive statistics were computed to define the study population. We performed a series of bivariate analyses to compare the 2 cohorts with respect to patient characteristics and study outcomes. Based on tests of normality, all continuous distributions (ie, age, BMI, and
A. Elnahas et al. Table 1
Bowel preparation and anastomotic leaks
3
Patient characteristics
Characteristics Demographics Median age (y) [IQR]† Male sex Median BMI (kg/m2) [IQR]† Current smoker Dependent functional status Comorbidities ASA classification R3 Diabetes Renal failure CAD CHF Hypertension Preoperative Low serum albumin (,3.5 g/dL) Chronic steroid use (%) Chemotherapy Radiotherapy Oral antibiotic preparation Laparoscopic surgery Colorectal cancer Inflammatory bowel disease Diverticular disease Operative Median operative time (min) [IQR] Enterocolic anastomosis Intraoperative transfusion Diverting stoma
MBP (n 5 2,581)
No MBP (n 5 1,935)
Total (N 5 4,516)
Missing values (%)
P value
60.0 [19.0] 1,226 (47.6) 27.5 [8.0] 460 (17.8) 31 (1.2)
59.0 [19.0] 956 (49.5) 27.4 [7.4] 348 (18.0) 23 (1.2)
N/A 2,182 (48.4) N/A 808 (17.9) 54 (1.2)
0 .31 .66 0 .16
.22 .19 .82 .89 .97
1,108 (43.0) 328 (12.7) 14 (.5) 48 (3.8) 185 (7.2) 1,186 (46.0)
826 (42.7) 249 (12.9) 14 (.7) 31 (3.6) 135 (7.0) 859 (44.4)
1,934 (42.9) 577 (12.8) 28 (.62) 79 (3.7) 320 (7.1) 2,045 (45.3)
.05 0 0 53.2 0 0
.87 .87 .44 .85 .81 .30
282 (15.9) 136 (5.3) 76 (3.0) 99 (8.2) 901 (38.3) 1,728 (67.0) 1,093 (42.4) 150 (5.8) 708 (27.4)
211 (15.3) 156 (8.1) 65 (3.4) 65 (7.8) 118 (6.2) 734 (37.9) 567 (29.3) 177 (9.2) 378 (19.5)
493 (15.6) 292 (6.5) 141 (3.1) 164 (8.1) 1,019 (23.9) 2,462 (54.5) 1,660 (36.8) 327 (7.2) 1,086 (24.1)
30.8 1.19 .71 54.7 16.8 .03 0 0 0
.62 ,.01* .43 .73 ,.01* ,.01* ,.01* ,.01* ,.01*
195.0 [116.0] 329 (12.8) 240 (9.3) 441 (17.1)
180.5 [107.0] 272 (14.1) 180 (9.3) 294 (15.2)
N/A 601 (13.3) 420 (9.3) 735 (16.3)
.42 0 0 0
.01* .20 .99 .09
ASA 5 American Society of Anesthesiologists; BMI 5 body mass index; CAD 5 coronary artery disease; CHF 5 congestive heart failure; IQR 5 interquartile range; MBP 5 mechanical bowel preparation. *Significance based on P value less than .05. † Based on Wilcoxon rank-sum test.
LOS) were non-normal, and accordingly, a nonparametric Wilcoxon rank-sum test was used to compare median values. The chi-square test was used to compare categorical data across groups. All study covariates were chosen a priori based on clinical relevance, and no selection techniques were used. Multiple imputation using data from all covariates was performed to handle missing data and improve the power of the analysis.12 Missing data were assumed to be missing at random, and the SAS PROC MI procedure was used to impute the missing data. Covariates with greater than 30% of missing observations were excluded from the imputation process as described in previous literature.13 A total of 20 imputed data sets were created to reduce sampling variability from the imputation process. Imputed values of binary data greater than or equal to .5 were set to 1, and anything less was set to 0.12 The parameter estimates from each imputed data set were averaged using the SAS PROC MIANALYZE procedure to produce the final estimate and standard error.14 Our final model was used to analyze both study outcomes and included the following covariates: MBP
use, age, sex, BMI, smoking, functional status, ASA classification, diabetes, renal failure, chronic steroid use, preoperative chemotherapy, oral antibiotic preparation, laparoscopic surgery, oncologic resection, resection for inflammatory bowel disease, resection for diverticular disease, enterocolic anastomosis, operative time, intraoperative transfusion, and diverting stoma. History of coronary artery disease, preoperative radiotherapy, and albumin were variables excluded from the final model because of their high number of missing values. Multicollinearity was examined among the independent variables, and no correlations were found based on a variance inflation factor threshold of 4. Given that the use of MBP was not randomly assigned, we performed a propensity score–based sensitivity analysis to evaluate the effect of confounding by indication. We used a regression adjustment method as described by D’Agostino et al.15 The propensity score represented the probability a patient was not prescribed MBP and was calculated using a multiple logistic regression model that included all demographic, comorbidity, and preoperative characteristics. The propensity score model fit in the
The American Journal of Surgery, Vol -, No -, - 2015
4 Table 2
Summary of outcomes
Outcomes
MBP (n 5 2,581)
No MBP (n 5 1,935)
Total (N 5 4,516)
P value
30-d Anastomotic leaks (%) 30-d Wound infections (%) 30-d Organ space infections (%) Median postoperative LOS (d) [IQR]†
79 (3.1) 199 (7.7) 121 (4.7) 5.0 [3.0]
98 (5.1) 165 (8.6) 98 (5.1) 5.0 [3.0]
177 (3.9) 364 (8.1) 219 (4.9) N/A
,.01* .25 .49 .54
IQR 5 interquartile range; LOS 5 length of stay; MBP 5 mechanical bowel preparation; N/A 5 not applicable. *Significance based on P value less than .05. † Based on Wilcoxon rank-sum test.
imputed data set was adequate and yielded a c-statistic of .754, indicating good discrimination. The predicted propensity scores were subsequently incorporated as a continuous covariate in the multivariable model with and without other covariates. A second sensitivity analysis was performed to assess the effect of imputation using only complete cases for the multivariable model. The omnibus test was significant for all logistic models, and assumptions of model fit were verified using the Hosmer–Lemeshow test and c-statistic. The distribution of postoperative LOS was found to be overdispersed based on the Lagrange test, and therefore, a negative binomial regression model was used for the analysis. Convergence criteria were met for all models, and there were no
Table 3
Summary of missing data
Variables
Percent of missing values
Age Sex BMI Smoking status Functional health status ASA classification Diabetes Renal failure CAD CHF Hypertension Low serum albumin level Chronic steroid use Preoperative chemotherapy Preoperative radiotherapy Oral antibiotics preparation Mechanical bowel preparation Planned laparoscopic surgery Oncologic surgery Pelvic anastomosis Operative time Intraoperative transfusion Diverting stoma Anastomotic leak Postoperative length of stay Mean
0 .31 .66 0 .16 .05 0 0 53.2 0 0 30.8 1.19 .71 54.7 16.8 17.6 .03 0 0 .42 0 0 0 .07 7.1
BMI 5 body mass index; CAD 5 coronary artery disease; CHF 5 congestive heart failure.
influential outliers. All statistical analyses were performed using SAS software, v9.3 (Cary, NC).
Results A total of 5,481 patients underwent an elective colon resection with a left-sided anastomosis during the study period. Only 4,516 patients had data on MBP use before surgery, and accordingly, the number of patients with and without preoperative MBP was 2,581 (56%) and 1,935 (49%), respectively (Table 1). The demographic and comorbid characteristics were similar between the 2 groups. A comparison of preoperative characteristics revealed statistical differences with respect to the following patient characteristics: chronic steroid use (5.3% vs 8.1%; P , .01), oral antibiotic preparation (38.3% vs 6.2%; P , .01), laparoscopic surgery (67.0% vs 37.9%; P , .01), resection for colorectal cancer (42.4% vs 29.3%; P , .01), resection for inflammatory bowel disease (5.8% vs 9.2%; P , .01), resection for diverticular disease (27.4% vs 19.5%; P , .01), and median operative time (116 vs 107 min; P 5 .01). With respect to study outcomes, 79 (3.1%) patients with preoperative MBP had an anastomotic leak within 30 days of surgery compared with 98 (5.1%) patients without MBP. Both groups had a median postoperative stay of 5 days (Table 2). Table 3 presents the results of the unadjusted, adjusted, propensity-adjusted, and complete-case analysis of MBP omission on 30-day anastomotic leaks and postoperative LOS. After covariate adjustment, MBP omission was associated with a 40% increase in odds of 30-day anastomotic leaks (odds ratio [OR] 1.40; P 5 .04, 95% confidence interval 1.01 to 1.93). However, no association was found with respect to postoperative LOS (OR, 1.00; P 5 .90; 95% CI, .97 to 1.04). The propensity score–adjusted models did not appreciably change the estimate or significance of the model. Furthermore, other predictors of 30-day anastomotic leaks were identified based on the multivariable analysis (Table 4). Chronic steroid use was significantly more likely to result in anastomotic leaks (OR, 2.58; P , .01; 95% CI, 1.31 to 5.08), whereas preoperative chemotherapy trended toward significance (P 5 .07). In contrast, the use of a diverting stoma displayed a significant protective effect (OR, .60; P 5 .04; 95% CI, .37 to .99).
A. Elnahas et al. Table 4
Bowel preparation and anastomotic leaks
5
30-Day anastomotic leaks and postoperative LOS in patients without MBP vs those with MBP
30-d Anastomotic leaks Unadjusted Adjusted for covariates Adjusted for propensity scores Adjusted for propensity scores and covariates Adjusted complete-case analysis† Postoperative LOS Unadjusted Adjusted for covariates Adjusted for propensity scores Adjusted for propensity scores and covariates Adjusted complete-case analysis†
OR
95% Confidence interval
P value
1.60 1.41 1.41 1.42 1.49
1.20–2.14 1.01–1.98 1.01–1.97 1.01–1.98 1.05–2.11
,.01* .04* .04* .04* .03*
IRR
95% Confidence interval
P value
.99 1.01 .98 1.00 1.01
.95–1.03 .97–1.04 .94–1.02 .97–1.04 .97–1.05
.52 .77 .34 .88 .61
IRR 5 incident rate ratio; LOS 5 length of stay; MBP 5 mechanical bowel preparation; OR 5 odds ratio. *Significance based on P value less than .05. † Model excluded covariates with greater than 30% missing data, n 5 4,173 (76.1%).
Comments Using data from a large surgical registry, patients who did not receive MBP before a left-sided colorectal anastomosis had a significantly higher rate of 30-day anastomotic leaks compared with those who received MBP. After adjustment for propensity scores and relevant clinical characteristics, MBP omission remained an independent predictor for 30-day anastomotic leaks. As well, our multivariable analysis showed that chronic steroid use was significantly associated with a higher leak rate, whereas diverting stomas appeared protective. Furthermore, the use of MBP did not have an effect on the patient LOS after surgery. Although anastomotic leaks are major contributors to prolonged hospital stay, the leak rate was low in both groups and was not enough to create a significant disparity in LOS. There have been many past studies addressing the issue of safety and feasibility of MBP in colorectal surgery. The Canadian Society of Colon and Rectal Surgeons performed an extensive review of the literature on this matter to develop clinical practice guidelines.16 The authors concluded that there was good evidence to support the omission of MBP overall; however, there was insufficient evidence to comment on patients specifically undergoing low anterior resections or laparoscopic surgery.16 Bucher et al3 conducted a randomized controlled trial on MBP exclusively in left-sided surgery and evaluated anastomotic leaks as a secondary outcome. In their study sample of 153 patients, 5 patients had an anastomotic leak when prescribed preoperative MBP compared with 1 patient in the group without MBP. The difference was not statistically significant, but the authors acknowledged that their study was underpowered for this outcome.3 The study also measured postoperative LOS and found it was significantly higher in patients who had MBP (14.9 vs 9.9, P 5 .02).
A recent Cochrane review on this subject concluded that MBP before elective colorectal surgery has no effect with respect to lowering anastomotic leakage rates.17 However, their meta-analysis of randomized trials included a large number of patients undergoing right-sided colon resections and various procedures without a primary anastomosis, which generally do not require bowel preparation.18,19 In addition, some trials excluded patients undergoing low anterior resections, and most trials were underpowered with a high chance of type II error because of small sample sizes.15,20,21 Therefore, generalizing their results to a population receiving low colorectal resections, which has a higher risk of leak, may not be practical. As with any observational study, there are some limitations to consider in our analysis. Classification of MBP use was based on chart abstraction, and no standard definition was provided in the registry including whether enemas alone were considered forms of bowel preparation. The type of MBP used in each patient was likely dependent on the surgeon and may have included other elements such as enemas and dietary restrictions. Although the use of oral antibiotics without MBP is an uncommon practice given that bowel preparations are used to ensure the antibiotic reaches the colon, there are cases where MBP is prescribed alone without oral antibiotics. To evaluate the independent effect of oral antibiotics, this variable was included separately in the multivariable model. Ultimately, our study objective was not to evaluate a particular MBP regimen but rather estimate the overall effect of MBP omission. In addition, some confounders and intermediate variables could not be accounted for in our study. For example, the ACS-NSQIP data did not capture details on intraoperative aspects, such as inferior mesenteric artery ligation, extent of proximal resection, or specific operative complications. Recently, these factors have been identified as potential independent predictors of anastomotic leak in
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colorectal surgery.22 As well, hospital volume in colorectal surgery could not be considered in the analysis because no institutional-level data are provided in the NSQIP database. As a confidentiality measure, NSQIP does not identify participating sites nor allows for blind identifiers because site associations are possible through advanced statistics. To our knowledge, this is the largest observational study evaluating the effect of MBP on anastomotic leaks in left-sided colorectal resections. To address potential confounding by indication, we also performed a propensity score–adjusted regression analysis to corroborate our results. Ideally, to eliminate bias from unmeasured confounding and demonstrate causality, a randomized controlled trial should be conducted in patients undergoing only left-sided colorectal resections. However, the low rate of anastomotic leaks after colorectal surgery would require a very large sample size to adequately power the study. Assuming an anastomotic leak rate of 5%, at least 1,812 patients would be needed to detect a 50% relative risk reduction with a 1tailed statistical test, an alpha level of .05, and a power of 80%. Therefore, demonstrating the safety of routine MBP omission for left-sided colorectal resections will demand further research of higher methodologic quality. An explanatory randomized trial would be the ideal study design to address this research question; however, a trial with the necessary sample size may not be feasible.
2. Contant CM, Hop WC, van’t Sant HP, et al. Mechanical bowel preparation for elective colorectal surgery: a multicentre randomised trial. Lancet 2007;370:2112–7. 3. Bucher P, Gervaz P, Soravia C, et al. Randomized clinical trial of mechanical bowel preparation versus no preparation before elective leftsided colorectal surgery. Br J Surg 2005;92:409–14. 4. Scabini S, Rimini E, Romairone E, et al. Colon and rectal surgery for cancer without mechanical bowel preparation: one-center randomized prospective trial. World J Surg Oncol 2010;8:35. 5. McCoubrey AS. The use of mechanical bowel preparation in elective colorectal surgery. Ulster Med J 2007;76:127–30. 6. Rullier E, Laurent C, Garrelon JL, et al. Risk factors for anastomotic leakage after resection of rectal cancer. Br J Surg 1998;85:355–8. 7. Khuri SF, Henderson WG, Daley J, et al. The patient safety in surgery study: background, study design, and patient populations. J Am Coll Surg 2007;204:1089–102. 8. Khuri SF, Daley J, Henderson W, et al. Risk adjustment of the postoperative mortality rate for the comparative assessment of the quality of surgical care: results of the National Veterans Affairs Surgical Risk Study. J Am Coll Surg 1997;185:315–27. 9. Daley J, Khuri SF, Henderson W, et al. Risk adjustment of the postoperative morbidity rate for the comparative assessment of the quality of surgical care: results of the National Veterans Affairs Surgical Risk Study. J Am Coll Surg 1997;185:328–40. 10. Daley J, Forbes MG, Young GJ, et al. Validating risk-adjusted surgical outcomes: site visit assessment of process and structure National VA Surgical Risk Study. J Am Coll Surg 1997;185:341–51. 11. Khuri SF, Henderson WG, Daley J, et al. Successful implementation of the Department of Veterans Affairs’ National Surgical Quality Improvement Program in the private sector: the patient safety in surgery study. Ann Surg 2008;248:329–36. 12. Schafer JL. Analysis of Incomplete Multivariate Data. London: Chapman and Hall; 1997. 13. Vesin A, Azoulay E, Ruckly S, et al. Reporting and handling missing values in clinical studies in intensive care units. Intensive Care Med 2013;39:1396–404. 14. Mitra R, Reiter JP. A comparison of two methods of estimating propensity scores after multiple imputation. Stat Methods Med Res; 2012:1–17. 15. D’Agostino Jr RB. Propensity score methods for bias reduction in the comparison of a treatment to a non-randomized control group. Stat Med 1998;17:2265–81. 16. Eskicioglu C, Forbes SS, Fenech DS, et al. Preoperative bowel preparation for patients undergoing elective colorectal surgery: a clinical practice guideline endorsed by the Canadian Society of Colon and Rectal Surgeons. Can J Surg 2010;53:385–95. 17. Gu¨enaga KF, Matos D, Wille-Jørgensen P. Mechanical bowel preparation for elective colorectal surgery. Cochrane Database Syst Rev; 2011:CD001544. 18. Jansen JO, O’Kelly TJ, Krukowski ZH, et al. Right hemicolectomy: mechanical bowel preparation is not required. J R Coll Surg Edinb 2002;47:557–60. 19. Mealy K, Salman A, Arthur G. Definitive one-stage emergency large bowel surgery. Br J Surg 1988;75:1216–9. 20. Zmora O, Mahajna A, Bar-Zakai B, et al. Colon and rectal surgery without mechanical bowel preparation. A randomised prospective trial. Ann Surg 2003;237:363–7. 21. Miettinen R, Laitinen ST, Makela JT, et al. Bowel preparation with oral polyethylene glycol electrolyte solution vs. no preparation in elective open colorectal surgery. Dis Colon Rectum 2000; 43:669–75. 22. Trencheva K, Morrissey KP, Wells M, et al. Identifying important predictors for anastomotic leak after colon and rectal resection: prospective study on 616 patients. Ann Surg 2013;257:108–13.
Conclusions The omission of MBP in colorectal surgery with a leftsided anastomosis was associated with a higher rate of 30day anastomotic leaks but not a longer stay in hospital. The reasons for higher rates of anastomotic leaks when MBP is omitted are not entirely clear. A large, well-designed, randomized controlled trial could test the hypothesis that MBP is truly protective against anastomotic leaks in leftsided colorectal procedures.
Acknowledgments Author contributions: Study conception and design: TDJ, AE, DU, AO, and FAQ; acquisition of data: AE and TDJ; analysis and interpretation of data: AE, TDJ, GL, and MM; drafting of manuscript: AE and TDJ; and critical revision for important intellectual content: TDJ, DU, AO, FAQ, GL, and MM. All authors have approved the final version of the manuscript to be published.
References 1. Halsted WS. Circular suture of the intestine: an experimental study. Am J Med Sci 1887;94:436–61 (Bucher 3).
The effect of mechanical bowel preparation on anastomotic leaks in elective left-sided colorectal resections Ahmad Elnahas, M.D., F.R.C.S.C.a, David Urbach, M.D., M.Sc., F.R.C.S.C.a, Gerald Lebovic, Ph.D.b, Muhammad Mamdani, Pharm.D., M.A., M.P.H.b, Allan Okrainec, M.D., M.H.P.E., F.R.C.S.C., F.A.C.S.a, Fayez A. Quereshy, M.D., M.B.A., F.R.C.S.C.a, Timothy D. Jackson, M.D., M.P.H., F.R.C.S.C., F.A.C.S.a,* a
Division of General Surgery, Department of Surgery, University Health Network, University of Toronto, 399 Bathurst Street, Toronto, Ontario, M5T 2S8, Canada; bApplied Health Research Centre, Keenan Research Centre, Li Ka Shing Knowledge Institute of St. Michael’s Hospital, Toronto, Ontario, Canada.
KEYWORDS: Bowel preparation; Anastomotic leaks; Colorectal surgery
Abstract BACKGROUND: Routine preoperative mechanical bowel preparation (MBP) for left-sided colorectal resections remains controversial. This study aims to evaluate the association between MBP and 30-day anastomotic leaks. METHODS: A retrospective cohort study was conducted using data from the National Surgical Quality Improvement Program from 2011 to 2012. Multiple imputation was used for missing data, and a multivariable logistic regression was performed to adjust for clinically relevant variables. A propensity score–adjusted model was performed as a sensitivity analysis. RESULTS: A total of 2,581 patients (57%) received preoperative MBP, whereas 1,935 (43%) did not. The 30-day anastomotic leak rate with and without preoperative MBP was 3.1% and 5.1%, respectively. After covariate adjustment, MBP omission was significantly associated with a 40% increased odds of 30-day anastomotic leaks (odds ratio 1.41, P 5 .04, 95% confidence interval 1.01 to 1.93). CONCLUSIONS: MBP omission was associated with a higher rate of 30-day anastomotic leaks. A large, well-designed, randomized controlled trial is needed to further evaluate this relationship. Ó 2015 Elsevier Inc. All rights reserved.
Disclaimer: American College of Surgeons’ National Surgical Quality Improvement Program (ACS NSQIP) and the hospitals participating in the ACS NSQIP are the source of the data used here; they have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors. There were no relevant financial relationships or any sources of support in the form of grants, equipment, or drugs. The authors declare no conflicts of interest. * Corresponding author. Tel.: 11-416-603-5599; fax: 11-416-603-6458 E-mail address: [email protected] Manuscript received January 21, 2015; revised manuscript March 23, 2015 0002-9610/$ - see front matter Ó 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.amjsurg.2015.03.030
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Surgeons commonly use mechanical bowel cleansing agents, such as polyethylene glycol and sodium phosphate, as a preoperative strategy to reduce postoperative infectious complications after colorectal anastomoses.1,2 Infectious wound complications, and especially anastomotic leakage, are considered major causes of morbidity after colorectal resections and can result in prolonged hospital stays.3,4 The widespread application of mechanical bowel preparation (MBP) has been attributed to its effect on decreasing intraluminal bacterial count, eliminating passage of solid feces, and improving bowel handling during construction of the anastomosis.3 As well, MBP is considered very beneficial in cases where colonic tumors are small, and performing an intraoperative colonoscopy may be necessary.5 The routine practice of MBP became controversial after several studies, including retrospective series and prospective randomized trials that demonstrated the safety and feasibility of colorectal surgery without preoperative bowel cleansing.3 Support against the use of MBP was further promoted based on better patient experience and the avoidance of side effects, such as preoperative dehydration, nausea, vomiting, and electrolyte abnormalities.5 As well, the advent of enhanced recovery programs and ‘‘fast-track’’ surgery has encouraged the practice of omitting MBP. However, with a higher risk of anastomotic leakage after left-sided colorectal resections, the routine omission of MBP in this specific subgroup warrants further evaluation.6 Additionally, MBP might offer better protection than diversion in the event of a leak by eliminating contamination from the potential column of stool above the anastomosis. Our primary study objective was to determine whether omission of MBP before elective colorectal resections with a left-sided anastomosis was associated with a higher rate of 30-day anastomotic leaks. Our secondary objective was to compare the postoperative length of stay (LOS) between groups.
44,208, 44,210, 44,145, 44,146, and 44,150. Diverting stomas (ie, ileostomy or colostomy) were identified either as part of the principal operative code (ie, 44,146 and 44,208) or a separate secondary code (ie, 44,310 and 44,320). Operations with noncolonic anastomoses (ie, ileoanal anastomoses) were excluded from the study.
Methods Study population We used data from the American College of Surgeons’ National Surgical Quality Improvement Program (ACSNSQIP) and colon-targeted participant use data files for the year 2011 and 2012 to conduct a retrospective cohort study. The ACS-NSQIP is a nationally validated, risk-adjusted database that captures 30-day clinical outcomes on patients undergoing major operations, and its methodology has been well described.7–11 Our study protocol was approved by the University Health Network Research Ethics Board. Our study population included patients who underwent an elective colorectal resection with a left-sided anastomosis in 2011 and 2012. Eligible operations included subtotal colectomies, partial left-sided resections, and low anterior resections. Operations were identified based on the following current procedural terminology codes: 44,207,
Outcomes The main outcome of our study was the 30-day anastomotic leak rate. The secondary outcome was the postoperative LOS.
Covariates We considered variables:
the
following
clinically
relevant
Demographics: Age Sex Body mass index (BMI) Current smoker within 1 year (yes/no) Functional health status (dependent/independent) Comorbidities: American Society of Anesthesiologists (ASA) classification (R3, 1 to 2) Diabetes requiring oral agents or insulin (yes/no) Renal failure (yes/no) Coronary artery disease (yes/no) Congestive heart failure (yes/no) Hypertension requiring medication (yes/no) Preoperative factors: Low-serum albumin level (,3.5 g/dL) (yes/no) Chronic steroid use greater than 10 days (yes/no) Chemotherapy within 90 days of surgery (yes/no) Radiotherapy within 90 days of surgery (yes/no) Oral antibiotic preparation (yes/no) Operative approach (laparoscopic/open) Colorectal cancer (yes/no) Inflammatory bowel disease (yes/no) Diverticular disease (yes/no) Operative factors: Operative time Intraoperative transfusion (yes/no) Enterocolic anastomosis (yes/no) Diverting stoma (yes/no)
Statistical analysis Patients satisfying the inclusion criteria were selected for analysis, and descriptive statistics were computed to define the study population. We performed a series of bivariate analyses to compare the 2 cohorts with respect to patient characteristics and study outcomes. Based on tests of normality, all continuous distributions (ie, age, BMI, and
A. Elnahas et al. Table 1
Bowel preparation and anastomotic leaks
3
Patient characteristics
Characteristics Demographics Median age (y) [IQR]† Male sex Median BMI (kg/m2) [IQR]† Current smoker Dependent functional status Comorbidities ASA classification R3 Diabetes Renal failure CAD CHF Hypertension Preoperative Low serum albumin (,3.5 g/dL) Chronic steroid use (%) Chemotherapy Radiotherapy Oral antibiotic preparation Laparoscopic surgery Colorectal cancer Inflammatory bowel disease Diverticular disease Operative Median operative time (min) [IQR] Enterocolic anastomosis Intraoperative transfusion Diverting stoma
MBP (n 5 2,581)
No MBP (n 5 1,935)
Total (N 5 4,516)
Missing values (%)
P value
60.0 [19.0] 1,226 (47.6) 27.5 [8.0] 460 (17.8) 31 (1.2)
59.0 [19.0] 956 (49.5) 27.4 [7.4] 348 (18.0) 23 (1.2)
N/A 2,182 (48.4) N/A 808 (17.9) 54 (1.2)
0 .31 .66 0 .16
.22 .19 .82 .89 .97
1,108 (43.0) 328 (12.7) 14 (.5) 48 (3.8) 185 (7.2) 1,186 (46.0)
826 (42.7) 249 (12.9) 14 (.7) 31 (3.6) 135 (7.0) 859 (44.4)
1,934 (42.9) 577 (12.8) 28 (.62) 79 (3.7) 320 (7.1) 2,045 (45.3)
.05 0 0 53.2 0 0
.87 .87 .44 .85 .81 .30
282 (15.9) 136 (5.3) 76 (3.0) 99 (8.2) 901 (38.3) 1,728 (67.0) 1,093 (42.4) 150 (5.8) 708 (27.4)
211 (15.3) 156 (8.1) 65 (3.4) 65 (7.8) 118 (6.2) 734 (37.9) 567 (29.3) 177 (9.2) 378 (19.5)
493 (15.6) 292 (6.5) 141 (3.1) 164 (8.1) 1,019 (23.9) 2,462 (54.5) 1,660 (36.8) 327 (7.2) 1,086 (24.1)
30.8 1.19 .71 54.7 16.8 .03 0 0 0
.62 ,.01* .43 .73 ,.01* ,.01* ,.01* ,.01* ,.01*
195.0 [116.0] 329 (12.8) 240 (9.3) 441 (17.1)
180.5 [107.0] 272 (14.1) 180 (9.3) 294 (15.2)
N/A 601 (13.3) 420 (9.3) 735 (16.3)
.42 0 0 0
.01* .20 .99 .09
ASA 5 American Society of Anesthesiologists; BMI 5 body mass index; CAD 5 coronary artery disease; CHF 5 congestive heart failure; IQR 5 interquartile range; MBP 5 mechanical bowel preparation. *Significance based on P value less than .05. † Based on Wilcoxon rank-sum test.
LOS) were non-normal, and accordingly, a nonparametric Wilcoxon rank-sum test was used to compare median values. The chi-square test was used to compare categorical data across groups. All study covariates were chosen a priori based on clinical relevance, and no selection techniques were used. Multiple imputation using data from all covariates was performed to handle missing data and improve the power of the analysis.12 Missing data were assumed to be missing at random, and the SAS PROC MI procedure was used to impute the missing data. Covariates with greater than 30% of missing observations were excluded from the imputation process as described in previous literature.13 A total of 20 imputed data sets were created to reduce sampling variability from the imputation process. Imputed values of binary data greater than or equal to .5 were set to 1, and anything less was set to 0.12 The parameter estimates from each imputed data set were averaged using the SAS PROC MIANALYZE procedure to produce the final estimate and standard error.14 Our final model was used to analyze both study outcomes and included the following covariates: MBP
use, age, sex, BMI, smoking, functional status, ASA classification, diabetes, renal failure, chronic steroid use, preoperative chemotherapy, oral antibiotic preparation, laparoscopic surgery, oncologic resection, resection for inflammatory bowel disease, resection for diverticular disease, enterocolic anastomosis, operative time, intraoperative transfusion, and diverting stoma. History of coronary artery disease, preoperative radiotherapy, and albumin were variables excluded from the final model because of their high number of missing values. Multicollinearity was examined among the independent variables, and no correlations were found based on a variance inflation factor threshold of 4. Given that the use of MBP was not randomly assigned, we performed a propensity score–based sensitivity analysis to evaluate the effect of confounding by indication. We used a regression adjustment method as described by D’Agostino et al.15 The propensity score represented the probability a patient was not prescribed MBP and was calculated using a multiple logistic regression model that included all demographic, comorbidity, and preoperative characteristics. The propensity score model fit in the
The American Journal of Surgery, Vol -, No -, - 2015
4 Table 2
Summary of outcomes
Outcomes
MBP (n 5 2,581)
No MBP (n 5 1,935)
Total (N 5 4,516)
P value
30-d Anastomotic leaks (%) 30-d Wound infections (%) 30-d Organ space infections (%) Median postoperative LOS (d) [IQR]†
79 (3.1) 199 (7.7) 121 (4.7) 5.0 [3.0]
98 (5.1) 165 (8.6) 98 (5.1) 5.0 [3.0]
177 (3.9) 364 (8.1) 219 (4.9) N/A
,.01* .25 .49 .54
IQR 5 interquartile range; LOS 5 length of stay; MBP 5 mechanical bowel preparation; N/A 5 not applicable. *Significance based on P value less than .05. † Based on Wilcoxon rank-sum test.
imputed data set was adequate and yielded a c-statistic of .754, indicating good discrimination. The predicted propensity scores were subsequently incorporated as a continuous covariate in the multivariable model with and without other covariates. A second sensitivity analysis was performed to assess the effect of imputation using only complete cases for the multivariable model. The omnibus test was significant for all logistic models, and assumptions of model fit were verified using the Hosmer–Lemeshow test and c-statistic. The distribution of postoperative LOS was found to be overdispersed based on the Lagrange test, and therefore, a negative binomial regression model was used for the analysis. Convergence criteria were met for all models, and there were no
Table 3
Summary of missing data
Variables
Percent of missing values
Age Sex BMI Smoking status Functional health status ASA classification Diabetes Renal failure CAD CHF Hypertension Low serum albumin level Chronic steroid use Preoperative chemotherapy Preoperative radiotherapy Oral antibiotics preparation Mechanical bowel preparation Planned laparoscopic surgery Oncologic surgery Pelvic anastomosis Operative time Intraoperative transfusion Diverting stoma Anastomotic leak Postoperative length of stay Mean
0 .31 .66 0 .16 .05 0 0 53.2 0 0 30.8 1.19 .71 54.7 16.8 17.6 .03 0 0 .42 0 0 0 .07 7.1
BMI 5 body mass index; CAD 5 coronary artery disease; CHF 5 congestive heart failure.
influential outliers. All statistical analyses were performed using SAS software, v9.3 (Cary, NC).
Results A total of 5,481 patients underwent an elective colon resection with a left-sided anastomosis during the study period. Only 4,516 patients had data on MBP use before surgery, and accordingly, the number of patients with and without preoperative MBP was 2,581 (56%) and 1,935 (49%), respectively (Table 1). The demographic and comorbid characteristics were similar between the 2 groups. A comparison of preoperative characteristics revealed statistical differences with respect to the following patient characteristics: chronic steroid use (5.3% vs 8.1%; P , .01), oral antibiotic preparation (38.3% vs 6.2%; P , .01), laparoscopic surgery (67.0% vs 37.9%; P , .01), resection for colorectal cancer (42.4% vs 29.3%; P , .01), resection for inflammatory bowel disease (5.8% vs 9.2%; P , .01), resection for diverticular disease (27.4% vs 19.5%; P , .01), and median operative time (116 vs 107 min; P 5 .01). With respect to study outcomes, 79 (3.1%) patients with preoperative MBP had an anastomotic leak within 30 days of surgery compared with 98 (5.1%) patients without MBP. Both groups had a median postoperative stay of 5 days (Table 2). Table 3 presents the results of the unadjusted, adjusted, propensity-adjusted, and complete-case analysis of MBP omission on 30-day anastomotic leaks and postoperative LOS. After covariate adjustment, MBP omission was associated with a 40% increase in odds of 30-day anastomotic leaks (odds ratio [OR] 1.40; P 5 .04, 95% confidence interval 1.01 to 1.93). However, no association was found with respect to postoperative LOS (OR, 1.00; P 5 .90; 95% CI, .97 to 1.04). The propensity score–adjusted models did not appreciably change the estimate or significance of the model. Furthermore, other predictors of 30-day anastomotic leaks were identified based on the multivariable analysis (Table 4). Chronic steroid use was significantly more likely to result in anastomotic leaks (OR, 2.58; P , .01; 95% CI, 1.31 to 5.08), whereas preoperative chemotherapy trended toward significance (P 5 .07). In contrast, the use of a diverting stoma displayed a significant protective effect (OR, .60; P 5 .04; 95% CI, .37 to .99).
A. Elnahas et al. Table 4
Bowel preparation and anastomotic leaks
5
30-Day anastomotic leaks and postoperative LOS in patients without MBP vs those with MBP
30-d Anastomotic leaks Unadjusted Adjusted for covariates Adjusted for propensity scores Adjusted for propensity scores and covariates Adjusted complete-case analysis† Postoperative LOS Unadjusted Adjusted for covariates Adjusted for propensity scores Adjusted for propensity scores and covariates Adjusted complete-case analysis†
OR
95% Confidence interval
P value
1.60 1.41 1.41 1.42 1.49
1.20–2.14 1.01–1.98 1.01–1.97 1.01–1.98 1.05–2.11
,.01* .04* .04* .04* .03*
IRR
95% Confidence interval
P value
.99 1.01 .98 1.00 1.01
.95–1.03 .97–1.04 .94–1.02 .97–1.04 .97–1.05
.52 .77 .34 .88 .61
IRR 5 incident rate ratio; LOS 5 length of stay; MBP 5 mechanical bowel preparation; OR 5 odds ratio. *Significance based on P value less than .05. † Model excluded covariates with greater than 30% missing data, n 5 4,173 (76.1%).
Comments Using data from a large surgical registry, patients who did not receive MBP before a left-sided colorectal anastomosis had a significantly higher rate of 30-day anastomotic leaks compared with those who received MBP. After adjustment for propensity scores and relevant clinical characteristics, MBP omission remained an independent predictor for 30-day anastomotic leaks. As well, our multivariable analysis showed that chronic steroid use was significantly associated with a higher leak rate, whereas diverting stomas appeared protective. Furthermore, the use of MBP did not have an effect on the patient LOS after surgery. Although anastomotic leaks are major contributors to prolonged hospital stay, the leak rate was low in both groups and was not enough to create a significant disparity in LOS. There have been many past studies addressing the issue of safety and feasibility of MBP in colorectal surgery. The Canadian Society of Colon and Rectal Surgeons performed an extensive review of the literature on this matter to develop clinical practice guidelines.16 The authors concluded that there was good evidence to support the omission of MBP overall; however, there was insufficient evidence to comment on patients specifically undergoing low anterior resections or laparoscopic surgery.16 Bucher et al3 conducted a randomized controlled trial on MBP exclusively in left-sided surgery and evaluated anastomotic leaks as a secondary outcome. In their study sample of 153 patients, 5 patients had an anastomotic leak when prescribed preoperative MBP compared with 1 patient in the group without MBP. The difference was not statistically significant, but the authors acknowledged that their study was underpowered for this outcome.3 The study also measured postoperative LOS and found it was significantly higher in patients who had MBP (14.9 vs 9.9, P 5 .02).
A recent Cochrane review on this subject concluded that MBP before elective colorectal surgery has no effect with respect to lowering anastomotic leakage rates.17 However, their meta-analysis of randomized trials included a large number of patients undergoing right-sided colon resections and various procedures without a primary anastomosis, which generally do not require bowel preparation.18,19 In addition, some trials excluded patients undergoing low anterior resections, and most trials were underpowered with a high chance of type II error because of small sample sizes.15,20,21 Therefore, generalizing their results to a population receiving low colorectal resections, which has a higher risk of leak, may not be practical. As with any observational study, there are some limitations to consider in our analysis. Classification of MBP use was based on chart abstraction, and no standard definition was provided in the registry including whether enemas alone were considered forms of bowel preparation. The type of MBP used in each patient was likely dependent on the surgeon and may have included other elements such as enemas and dietary restrictions. Although the use of oral antibiotics without MBP is an uncommon practice given that bowel preparations are used to ensure the antibiotic reaches the colon, there are cases where MBP is prescribed alone without oral antibiotics. To evaluate the independent effect of oral antibiotics, this variable was included separately in the multivariable model. Ultimately, our study objective was not to evaluate a particular MBP regimen but rather estimate the overall effect of MBP omission. In addition, some confounders and intermediate variables could not be accounted for in our study. For example, the ACS-NSQIP data did not capture details on intraoperative aspects, such as inferior mesenteric artery ligation, extent of proximal resection, or specific operative complications. Recently, these factors have been identified as potential independent predictors of anastomotic leak in
6
The American Journal of Surgery, Vol -, No -, - 2015
colorectal surgery.22 As well, hospital volume in colorectal surgery could not be considered in the analysis because no institutional-level data are provided in the NSQIP database. As a confidentiality measure, NSQIP does not identify participating sites nor allows for blind identifiers because site associations are possible through advanced statistics. To our knowledge, this is the largest observational study evaluating the effect of MBP on anastomotic leaks in left-sided colorectal resections. To address potential confounding by indication, we also performed a propensity score–adjusted regression analysis to corroborate our results. Ideally, to eliminate bias from unmeasured confounding and demonstrate causality, a randomized controlled trial should be conducted in patients undergoing only left-sided colorectal resections. However, the low rate of anastomotic leaks after colorectal surgery would require a very large sample size to adequately power the study. Assuming an anastomotic leak rate of 5%, at least 1,812 patients would be needed to detect a 50% relative risk reduction with a 1tailed statistical test, an alpha level of .05, and a power of 80%. Therefore, demonstrating the safety of routine MBP omission for left-sided colorectal resections will demand further research of higher methodologic quality. An explanatory randomized trial would be the ideal study design to address this research question; however, a trial with the necessary sample size may not be feasible.
2. Contant CM, Hop WC, van’t Sant HP, et al. Mechanical bowel preparation for elective colorectal surgery: a multicentre randomised trial. Lancet 2007;370:2112–7. 3. Bucher P, Gervaz P, Soravia C, et al. Randomized clinical trial of mechanical bowel preparation versus no preparation before elective leftsided colorectal surgery. Br J Surg 2005;92:409–14. 4. Scabini S, Rimini E, Romairone E, et al. Colon and rectal surgery for cancer without mechanical bowel preparation: one-center randomized prospective trial. World J Surg Oncol 2010;8:35. 5. McCoubrey AS. The use of mechanical bowel preparation in elective colorectal surgery. Ulster Med J 2007;76:127–30. 6. Rullier E, Laurent C, Garrelon JL, et al. Risk factors for anastomotic leakage after resection of rectal cancer. Br J Surg 1998;85:355–8. 7. Khuri SF, Henderson WG, Daley J, et al. The patient safety in surgery study: background, study design, and patient populations. J Am Coll Surg 2007;204:1089–102. 8. Khuri SF, Daley J, Henderson W, et al. Risk adjustment of the postoperative mortality rate for the comparative assessment of the quality of surgical care: results of the National Veterans Affairs Surgical Risk Study. J Am Coll Surg 1997;185:315–27. 9. Daley J, Khuri SF, Henderson W, et al. Risk adjustment of the postoperative morbidity rate for the comparative assessment of the quality of surgical care: results of the National Veterans Affairs Surgical Risk Study. J Am Coll Surg 1997;185:328–40. 10. Daley J, Forbes MG, Young GJ, et al. Validating risk-adjusted surgical outcomes: site visit assessment of process and structure National VA Surgical Risk Study. J Am Coll Surg 1997;185:341–51. 11. Khuri SF, Henderson WG, Daley J, et al. Successful implementation of the Department of Veterans Affairs’ National Surgical Quality Improvement Program in the private sector: the patient safety in surgery study. Ann Surg 2008;248:329–36. 12. Schafer JL. Analysis of Incomplete Multivariate Data. London: Chapman and Hall; 1997. 13. Vesin A, Azoulay E, Ruckly S, et al. Reporting and handling missing values in clinical studies in intensive care units. Intensive Care Med 2013;39:1396–404. 14. Mitra R, Reiter JP. A comparison of two methods of estimating propensity scores after multiple imputation. Stat Methods Med Res; 2012:1–17. 15. D’Agostino Jr RB. Propensity score methods for bias reduction in the comparison of a treatment to a non-randomized control group. Stat Med 1998;17:2265–81. 16. Eskicioglu C, Forbes SS, Fenech DS, et al. Preoperative bowel preparation for patients undergoing elective colorectal surgery: a clinical practice guideline endorsed by the Canadian Society of Colon and Rectal Surgeons. Can J Surg 2010;53:385–95. 17. Gu¨enaga KF, Matos D, Wille-Jørgensen P. Mechanical bowel preparation for elective colorectal surgery. Cochrane Database Syst Rev; 2011:CD001544. 18. Jansen JO, O’Kelly TJ, Krukowski ZH, et al. Right hemicolectomy: mechanical bowel preparation is not required. J R Coll Surg Edinb 2002;47:557–60. 19. Mealy K, Salman A, Arthur G. Definitive one-stage emergency large bowel surgery. Br J Surg 1988;75:1216–9. 20. Zmora O, Mahajna A, Bar-Zakai B, et al. Colon and rectal surgery without mechanical bowel preparation. A randomised prospective trial. Ann Surg 2003;237:363–7. 21. Miettinen R, Laitinen ST, Makela JT, et al. Bowel preparation with oral polyethylene glycol electrolyte solution vs. no preparation in elective open colorectal surgery. Dis Colon Rectum 2000; 43:669–75. 22. Trencheva K, Morrissey KP, Wells M, et al. Identifying important predictors for anastomotic leak after colon and rectal resection: prospective study on 616 patients. Ann Surg 2013;257:108–13.
Conclusions The omission of MBP in colorectal surgery with a leftsided anastomosis was associated with a higher rate of 30day anastomotic leaks but not a longer stay in hospital. The reasons for higher rates of anastomotic leaks when MBP is omitted are not entirely clear. A large, well-designed, randomized controlled trial could test the hypothesis that MBP is truly protective against anastomotic leaks in leftsided colorectal procedures.
Acknowledgments Author contributions: Study conception and design: TDJ, AE, DU, AO, and FAQ; acquisition of data: AE and TDJ; analysis and interpretation of data: AE, TDJ, GL, and MM; drafting of manuscript: AE and TDJ; and critical revision for important intellectual content: TDJ, DU, AO, FAQ, GL, and MM. All authors have approved the final version of the manuscript to be published.
References 1. Halsted WS. Circular suture of the intestine: an experimental study. Am J Med Sci 1887;94:436–61 (Bucher 3).
