Abstract
Purpose:
This planned scoping review aims to map the current knowledge on preoperative risk factors associated with anastomotic leakage following colorectal cancer surgery.
Methods:
The review will adhere to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Extensions for Scoping Reviews guidelines. The search will be conducted using MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials databases. Additionally, we will include grey literature sources. Only original studies examining a risk factor for anastomotic leakage will be included. Data will be charted based on trial characteristics, demographic data, population size, the investigated risk factors, and potential interventions.
Results:
The structured overview will be presented as a narrative summary with supplementary statistics.
Conclusion:
This protocol describes the methodology for a scoping review which aims to map primary research on preoperative risk factors for anastomotic leakage following colorectal surgery. By systematically collecting and presenting the existing evidence, this review seeks to identify key findings and highlight research gaps to guide clinicians and researchers.
Keywords: anastomotic leakage, colorectal cancer, postoperative complication, prediction, risk factors
Introduction
Rationale
Anastomotic leakage (AL) following surgery for colorectal cancer remains a significant complication with often severe consequences. This complication significantly increases patient morbidity and mortality, prolongs hospital and ICU stays, reduces quality of life, and elevates cancer recurrence risk[1].
To predict AL preoperatively, we must evaluate both modifiable and non-modifiable risk factors. Non-modifiable risk factors, such as male sex, a high American Society of Anesthesiologists score, comorbidities, and high age, cannot, or not easily, be influenced[2,3]. AL risk also varies by anatomical location, with right colonic anastomoses having the lowest risk and rectal anastomoses having the highest[4].
Known modifiable risk factors include smoking, alcohol consumption, obesity, preoperative radiotherapy, low preoperative total serum protein, and the use of steroids or non-steroidal anti-inflammatory drugs [2,5]. Attempting to manage these risk factors may help reduce AL risk.
As a potential risk factor for AL, the intestinal microbiome has increasingly become a research focus. A healthy microbiome maintains epithelial integrity, preventing paracellular leakage and enhancing resistance to toxins and pathogens[6,7]. Microbiome alterations can promote inflammation and lead to infection[8]. This can contribute to various postoperative complications, including AL, wound infection, peritonitis, superinfections, or sepsis[9].
It has been shown that specific surgical procedures, such as extensive tumor resection, emergency surgery, and surgical resection types such as resection of the transverse colon, left hemicolectomy, subtotal colectomy, and low anterior resection with anastomosis to the rectum can increase the risk of AL[3]. Intraoperative complications, such as increased blood loss and longer operation time, further increase this risk[5]. A laparoscopic approach has not yet been proven to reduce the occurrence of postoperative AL[10]. Creating a temporary, proximal stoma, commonly used in patients with a low anterior resection, seems to be a protective factor, as patients with it rarely require reoperation for sepsis control[11].
Finally, environmental factors seem to influence the occurrence of AL, such as the number of hospital beds in the treating hospital[5].
Objective
The purpose of this scoping review is to explore and map the current knowledge on preoperative risk factors for AL following colorectal cancer surgery. The findings will be structured and analyzed to provide clinicians and researchers with a comprehensive overview of the current state of evidence and to make the existing knowledge accessible for broad consideration and practical application in clinical settings.
The research question will be addressed in the following subsections, each focusing on a specific aspect of AL after surgery for colorectal cancer:
What are the definitions used for AL?
Which preoperative risk factors for AL are known?
How is AL diagnosed, and how is it diagnosed in patients with a protective stoma?
How strong is the evidence for the influence of the identified risk factors?
Is there a difference in the level of evidence for modifiable and non-modifiable risk factors?
How does a protective stoma affect the incidence of AL, and how do preoperative risk factors differ in their impact between patients with and without protective stoma?
Methods
This protocol has been prepared according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols statement[12].
The systematic scoping review will follow the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews[13].
PROSPERO waived registration due to the scoping review design. However, this protocol was registered and uploaded to the Open Science Framework.
Eligibility criteria
We will include peer-reviewed primary research studies with quantitative, qualitative, and mixed-methods designs that investigate preoperative risk factors for AL following surgery for colorectal cancer.
All studies must report at least one risk factor associated with AL which was present before the surgery.
We will include all available records up to the date of submission of the scoping review, regardless of publication year.
Eligible full-text studies in English, German, Danish, Norwegian, or Swedish will be assessed; we will attempt to consider studies in all languages by obtaining translations or contacting the authors for information in English.
Reviews, guidelines, commentaries, textbooks, editorials, letters, conference abstracts, and other non-peer-reviewed literature will be excluded but may be used to identify relevant primary research.
Studies involving children (<18 years of age) will be excluded.
Information sources
We will conduct our search in the following databases: MEDLINE (indexing from 1947), EMBASE (indexing from 1946 on), and the Cochrane Central Register of Controlled Trials (no formal indexing cutoff). We will aim to identify other primary research in grey literature, utilize Web of Science (indexing from 1990 on) for reference detection and analysis, and employ backward and forward snowballing to uncover studies not identified through our initial search strategy. The search will be repeated before the submission of the scoping review to ensure it reflects the most recent state of literature on the topic.
Search strategy
The search strategy is developed with the help of a health sciences librarian experienced in conducting scoping reviews.
The detailed search string for EMBASE is provided in Table 1, showing results from a preliminary search in November 2024.
Table 1.
Search string and preliminary results from November 2024
| Search No. | Search string | Results embase |
|---|---|---|
| 1 | Anastomosis leakage/ | 29 082 |
| 2 | Risk factor/ | 1 481 955 |
| 3 | Large intestine cancer/ | 678 |
| 4 | Colon tumor/ | 24 113 |
| 5 | Cecum tumor/ | 1324 |
| 6 | Sigmoid tumor/ | 114 |
| 7 | Rectosigmoid cancer/ | 184 |
| 8 | Colorectal tumor/ | 31 738 |
| 9 | Rectum tumor/ | 16 161 |
| 10 | 3 OR 4 OR 5 OR 6 OR 7 OR 8 OR 9 | 69 337 |
| 11 | (anastomosis leak* OR anastomotic leak*).ab,kf,ti. | 22 006 |
| 12 | (relative risk* OR risk factor* OR risk factor score* OR risk score* OR social risk factor*).ab,kf,ti. | 1 425 876 |
| 13 | (large intestin* cancer* OR cancer* of the large intestine OR large intestin* mass* OR mass* of the large intestine OR large intestin* carcinoma* OR carcinoma* of the large intestine OR large intestin* adenocarcinoma* OR adenocarcinoma* of the large intestine OR large intestin* tumo?r* OR tumo?r* of the large intestine OR large intestin* neoplas* OR neoplas* of the large intestine OR large intestin* malignanc* OR malignanc* of the large intestine) .ab,kf,ti. | 1431 |
| 14 | (large bowel cancer* OR cancer* of the large bowel OR large bowel mass* OR mass* of the large bowel OR large bowel carcinoma* OR carcinoma* of the large bowel OR large bowel adenocarcinoma* OR adenocarcinoma* of the large bowel OR large bowel tumo?r* OR tumo?r* of the large bowel OR large bowel neoplas* OR neoplas* of the large bowel OR large bowel malignanc* OR malignanc* of the large bowel) .ab,kf,ti. | 2329 |
| 15 | (Colon* cancer* OR cancer* of the colon OR canc* colon* OR colon* mass* OR mass* of the colon OR colon* carcinoma* OR carcinoma* of the colon OR carcinoma* colon* OR colon* adenocarcinoma* OR adenocarcinoma* of the colon OR adenocarcinoma* colon* OR colon* tumo?r* OR tumo?r* in the colon OR tumor* colon* OR colon* neoplas* OR neoplas* in the colon OR neoplasia* colon* OR colon* malignanc* OR malignanc* in the colon OR malignita* colon*).ab,kf,ti. | 139 741 |
| 16 | (caecal cancer* OR caecum cancer* OR cancer* of the caecum OR cancer* of the cecum OR cecal cancer* OR cecum cancer* OR canc* caec* OR caecal mass* OR caecum mass* OR mass* of the caecum OR mass* of the cecum OR cecal mass* OR cecum mass* OR caecal carcinoma* OR caecum carcinoma* OR carcinoma* of the caecum OR carcinoma* of the cecum OR cecal carcinoma* OR cecum carcinoma* OR carcimona* caec* OR caecal adenocarcinoma* OR caecum adenocarcinoma* OR adenocarcinoma* of the caecum OR adenocarcinoma* of the cecum OR cecal adenocarcinoma* OR cecum adenocarcinoma* OR adenocarcinoma* caec* OR caecal tumo?r* OR caecum tumo?r* OR tumo?r* of the caecum OR tumo?r* of the cecum OR cecal tumo?r* OR cecum tumo?r* OR tumor* caecal* OR caecal neoplas* OR caecum neoplas* OR neoplas* of the caecum OR neoplas* of the cecum OR cecal neoplas* OR cecum neoplas* OR neoplasia* caec* OR caecal malignanc* OR caecum malignanc* OR malignanc* of the caecum OR malignanc* of the cecum OR cecal malignanc* OR cecum malignanc* OR malignita* caec*).ab,kf,ti. | 2407 |
| 17 | (mesocolon* cancer* OR cancer* of the mesocolon OR canc* mesocol* OR mesocolon* mass* OR mass* of the mesocolon OR mesocolon* carcinoma* OR carcinoma* of the mesocolon OR carcinoma* mesocol* OR mesocolon* adenocarcinoma* OR adenocarcinoma* of the mesocolon OR adenocarcinoma* mesocol* OR mesocolon* tumo?r* OR tumo?r* of the mesocolon OR tumor* mesocol* OR mesocolon* neoplas* OR neoplas* of the mesocolon OR neoplasia* mesocol* OR mesocolon* malignanc* OR malignanc* of the mesocolon OR malignita* mesocol*).ab,kf,ti. | 62 |
| 18 | (cancer* of the sigmoid colon OR cancer* of the sigmoid OR sigmoid colon cancer* OR sigmoid* cancer* OR canc* sigmoide* OR mass* of the sigmoid colon OR mass* of the sigmoid OR sigmoid colon mass* OR sigmoid* mass* OR carcinoma* of the sigmoid colon OR carcinoma* of the sigmoid OR sigmoid colon carcinoma* OR sigmoid* carcinoma* OR carcinoma* sigmoide* OR adenocarcinoma* of the sigmoid colon OR adenocarcinoma* of the sigmoid OR sigmoid colon adenocarcinoma* OR sigmoid* adenocarcinoma* OR adenocarcinoma* sigmoide* OR tumo?r* of the sigmoid colon OR tumo?r* of the sigmoid OR sigmoid colon tumo?r* OR sigmoid* tumo?r* OR tumor* sigmoide* OR neoplas* of the sigmoid colon OR neoplas* of the sigmoid OR sigmoid colon neoplas* OR sigmoid* neoplas* OR neoplasia* sigmoide* OR malignanc* of the sigmoid colon OR malignanc* of the sigmoid OR sigmoid colon malignanc* OR sigmoid* malignanc* OR malignita* sigmoide*).ab,kf,ti. | 4303 |
| 19 | (rectosigmoid* cancer* OR recto-sigmoid* cancer* OR cancer* of the rectosigmoid* OR cancer* of the recto-sigmoid* OR canc* rectosigmoide* OR rectosigmoid* mass* OR recto-sigmoid* mass* OR mass* of the rectosigmoid OR mass* of the recto-sigmoid OR rectosigmoid* carcinoma* OR recto-sigmoid* carcinoma* OR carcinoma* of the rectosigmoid OR carcinoma* of the recto-sigmoid OR carcinoma* rectosigmoide* OR rectosigmoid* adenocarcinoma* OR recto-sigmoid* adenocarcinoma* OR adenocarcinoma* of the rectosigmoid OR adenocarcinoma* of the recto-sigmoid OR adenocarcinoma* rectosigmoide* OR rectosigmoid* tumo?r* OR recto-sigmoid* tumo?r* OR tumo?r* of the rectosigmoid OR tumo?r* of the recto-sigmoid OR tumor* rectosigmoide* OR rectosigmoid* neoplas* OR recto-sigmoid* neoplas* OR neoplas* of the rectosigmoid OR neoplas* of the recto-sigmoid OR neoplasia* rectosigmoide* OR rectosigmoid* malignanc* OR recto-sigmoid* malignanc* OR malignanc* of the rectosigmoid OR malignanc* of the recto-sigmoid OR malignita* rectosigmoide*).ab,kf,ti. | 1390 |
| 20 | (Colorect* cancer* OR rectocolon* cancer* OR cancer* of the colorectum OR canc* colorect* OR colorect* mass* OR rectocolon* mass* OR mass* of the colorectum OR colorect* carcinoma* OR rectocolon* carcinoma* OR carcinoma* of the colorectum OR carcinoma* colorect* OR colorect* adenocarcinoma* OR rectocolon* adenocarcinoma* OR adenocarcinoma* of the colorectum OR adenocarcinoma* colorect* OR colorect* tumo?r* OR rectocolon* tumo?r* OR tumo?r* of the colorectum OR tumor* colorect* OR colorect* neoplas* OR rectocolon* neoplas* OR neoplas* of the colorectum OR neoplasia* colorect* OR colorect* malignanc* OR rectocolon* malignanc* OR malignanc* of the colorectum OR malignita* colorect*).ab,kf,ti. | 256 939 |
| 21 | (cancer* of the rectum OR rectum-cancer* OR rectal cancer* OR cancer* of the upper rectum OR cancer* of the lower rectum OR canc* rect* OR mass* of the rectum OR rectum-mass* OR rectal mass* OR mass* of the upper rectum OR mass* of the lower rectum OR carcinoma* of the rectum OR rectum-carcinoma* OR rectal carcinoma* OR carcinoma* of the upper rectum OR carcinoma* of the lower rectum OR carcinoma* rect* OR adenocarcinoma* of the rectum OR rectum-adenocarcinoma* OR rectal adenocarcinoma* OR adenocarcinoma* of the upper rectum OR adenocarcinoma* of the lower rectum OR adenocarcinoma* rect* OR tumo?r* of the rectum OR rectum-tumo?r* OR rectal tumo?r* OR tumo?r* of the upper rectum OR tumo?r* of the lower rectum OR tumor* rect* OR neoplas* of the rectum OR rectum-neoplas* OR rectal neoplas* OR neoplas* of the upper rectum OR neoplas* of the lower rectum OR neoplasia* rect* OR malignanc* of the rectum OR rectum-malignanc* OR rectal malignanc* OR malignanc* of the upper rectum OR malignanc* of the lower rectum OR malignita* rect*).ab,kf,ti. | 66 072 |
| 22 | 13 OR 14 OR 15 OR 16 OR 17 OR 18 OR 19 OR 20 OR 21 | 409 049 |
| 23 | 1 OR 11 | 34 482 |
| 24 | 2 OR 12 | 2 045 870 |
| 25 | 10 OR 22 | 427 796 |
| 26 | 23 AND 24 AND 25 | 1535 |
Note: * and ? are used to include possible variations of the word
In this example, relevant Emtree terms were identified, and Boolean operators (AND, OR) were used to combine search terms effectively. The strategy was tested and adjusted to optimize search results.
A limitation of our search is the search terms’ entry year. The Emtree terms “anastomosis leakage” and “risk factor” were first introduced in 1974, while “colorectal cancer” was added in 1983. We aim to capture relevant literature published before these dates by incorporating synonyms.
Our search strategy does not specify the risk factors to be preoperative. This approach was chosen to ensure that all related literature is included. The preoperative nature of the risk factors will instead be evaluated during the literature screening process.
We will conduct backward and forward snowballing and explore grey literature to enhance the comprehensiveness of this approach.
Data management
The results from the primary search will be uploaded to Covidence[14], where screening and data extraction will occur. Data extraction will be supported by a Microsoft Excel[15] sheet to record information systematically. Included studies will be filed and organized in Zotero[16]. Statistical analysis and data visualization will be performed using the open-access software R[17].
Selection process
After removing duplicates, two independent reviewers will screen titles and abstracts for eligibility, followed by a full-text assessment of the selected articles in the same manner.
Disagreements will be resolved through discussion or, if necessary, by consulting a third reviewer.
Data collection process
A predefined data extraction form will be developed and pilot-tested (Table 2). Two reviewers will independently chart all included studies and then compare and discuss their results. A third independent reviewer will resolve any conflicts.
Table 2.
Data extraction form
| Author |
|---|
| Year |
| Name |
| Journal |
| Study design |
| Setting |
| Country |
| Are AL risk factors the primary outcome? (yes/no) |
| Aim |
| Population |
|
| Diagnosis |
|
| Risk factors (RF) |
|
| (The list can be expanded, and items will be specified based on analyzed RF.) |
| Scoring/prediction system used? |
| Operative procedure |
| Protective stoma |
|
| Preoperative interventions |
|
| Postoperative care |
|
| Early postoperative clinical progression |
| Postoperative complications (except AL) |
| AL |
|
| Post-complication development |
| Long-term outcomes |
| Key findings |
| Secondary findings |
| Limitations |
The publication’s authors will be contacted for further information if the data presentation is insufficient or unclear.
All results of the data charting process will be reviewed and discussed by all authors of the scoping review.
Data items
Data extraction will be conducted, and data will be charted into predefined categories, including but not limited to: Title and first author’s name, year and country of publication, study design (e.g., prospective, retrospective, randomized controlled trials, qualitative, quantitative), setup (e.g., patient volume, multicenter), population size, demographic data, preoperative health status (recorded comorbidities and other risk factors), any preemptive interventions, details on surgery type and procedure, postoperative care and clinical progression, timing and diagnosis of AL, surgical treatment solution, post-complication development, long-term outcomes, and quality-of-life measurements, if available. A preliminary data extraction sheet is provided in Table 2.
A critical appraisal of the trials’ results will be conducted.
Outcomes and prioritization
The primary objective of this planned scoping review is to map the evidence of preoperative risk factors for AL. We will prioritize the presentation of the examined risk factors and their impact on the occurrence of AL.
Secondarily, we report possible intervention methods and clinical developments throughout the treatment process. These data points will be presented in relation to the demographic data, trial characteristics, and setup. If long-term outcomes are available, we will include these, specifically if they relate to the investigated risk factors or interventions. We reserve the option to adjust the prioritization or amend the secondary focus areas of our scope should previously unidentified focal points or gaps in the literature emerge.
Risk of bias in individual studies
Identifying potential sources of bias is integral to the mapping process, as they highlight weaknesses in the current state of research. These biases will, therefore, be identified during and reevaluated after the data charting process.
However, we will not discuss the quality of individual studies, as the purpose of any scoping review is solely to map the evidence and show strengths and gaps. We will present a narrative evaluation of biases and other weaknesses in the reviewed literature.
Data synthesis
The extracted data will be synthesized to highlight similarities and discrepancies.
A thematic analysis will be performed to organize and categorize the identified risk factors. We will not undertake a meta-analysis, as this is not part of the objective of a scoping review.
Discussion
This scoping review will map the existing literature by providing an extensive overview of preoperative risk factors for AL. A key challenge is the reliability of the classification and the coding of the heterogeneous material in web-based search engines. The varying entry dates for search terms might introduce a bias toward studies conducted within the past 40–50 years. Identifying grey literature is a difficult task, with a risk of relevant sources being overlooked; however, it enhances the comprehensiveness of the search, as does backward and forward snowballing. Narrowing the eligibility criteria to preoperative risk factors could increase the likelihood of human error in the study selection process. We intend to mitigate these challenges by involving an experienced librarian skilled in conducting scoping reviews and employing multiple reviewers for screening and data extraction.
Conclusion
Anastomotic leakage after colorectal cancer surgery is a widely known and feared complication. The planned scoping review aims to identify the preoperative risk factors associated with AL to enhance the understanding of their impacts and possible interventions.
As this field of surgical research continues to expand, the review can only aim to mirror the current state of comprehension. The objective is to support researchers and clinicians in better understanding the established risk factors that can determine patient outcomes.
Footnotes
OSF-identifier: osf.io/sp2ca
Published online 20 March 2025
Contributor Information
Veronica Ott, Email: veot@regsj.dk.
Anders Bech Jørgensen, Email: dr.bech@gmail.com.
Lennart Friis-Hansen, Email: doclennart@gmail.com.
Birgitte Brandstrup, Email: bbrn@regsj.dk.
Ethical approval
None.
Consent
None.
Sources of funding
The research going into the scoping review is supported by the Department of Surgery of Holbæk Hospital and the Danish Cancer Society.
Author contributions
V.T.: study concept, design of a search strategy, and writing the protocol; A.B.J., L.F.H., B.B.: study concept, design of a search strategy, and writing of the protocol.
Conflicts of interest disclosure
All authors declare no competing interests.
Research registration unique identifying number (UIN)
None.
Guarantor
Veronica Ott, Birgitte Brandstrup.
Provenance and peer review
None.
Data availability statement
No original data are generated or analyzed in the making of this scoping review.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
No original data are generated or analyzed in the making of this scoping review.