title: Systematic review of preoperative, intraoperative and postoperative risk factors for colorectal anastomotic leaks.
abstract: BACKGROUND
  Anastomotic leak (AL) represents a dreaded complication following colorectal surgery, with a prevalence of 1-19 per cent. There remains a lack of consensus regarding factors that may predispose to AL and the relative risks associated with them. The objective was to perform a systematic review of the literature, focusing on the role of preoperative, intraoperative and postoperative factors in the development of colorectal ALs.
  
  
  METHODS
  A systematic review was performed to identify adjustable and non-adjustable preoperative, intraoperative and postoperative factors in the pathogenesis of AL. Additionally, a severity grading system was proposed to guide treatment.
  
  
  RESULTS
  Of 1707 papers screened, 451 fulfilled the criteria for inclusion in the review. Significant preoperative risk factors were: male sex, American Society of Anesthesiologists fitness grade above II, renal disease, co-morbidity and history of radiotherapy. Tumour-related factors were: distal site, size larger than 3 cm, advanced stage, emergency surgery and metastatic disease. Adjustable risk factors were: smoking, obesity, poor nutrition, alcohol excess, immunosuppressants and bevacizumab. Intraoperative risk factors were: blood loss/transfusion and duration of surgery more than 4 h. Stomas lessen the consequences but not the prevalence of AL. In the postoperative period, CT is the most commonly used imaging tool, with or without rectal contrast, and a C-reactive protein level exceeding 150 mg/l on day 3-5 is the most sensitive biochemical marker. A five-level classification system for AL severity and appropriate management is presented.
  
  
  CONCLUSIONS
  Specific risk factors and their potential correction or indications for stoma were identified. An AL severity score is proposed to aid clinical decision-making.
authors.affiliation: Centre for Colorectal Disease, St Vincent's University Hospital, Dublin, Ireland.
authors.forename: F D
authors.initials: FD
authors.lastname: McDermott
authors.forename: A
authors.initials: A
authors.lastname: Heeney
authors.forename: M E
authors.initials: ME
authors.lastname: Kelly
authors.forename: R J
authors.initials: RJ
authors.lastname: Steele
authors.forename: G L
authors.initials: GL
authors.lastname: Carlson
authors.forename: D C
authors.initials: DC
authors.lastname: Winter
mesh_terms: D000367:Age Factors; D000368:Aged; D057868:Anastomotic Leak / Q000209:etiology*; D015415:Biomarkers / Q000378:metabolism; D002097:C-Reactive Protein / Q000378:metabolism; D003106:Colon / Q000601:surgery*; D015179:Colorectal Neoplasms / Q000601:surgery; D004638:Emergency Treatment / Q000009:adverse effects; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D061646:Operative Time; D019990:Perioperative Care / Q000706:statistics & numerical data*; D012007:Rectum / Q000601:surgery*; D012307:Risk Factors; D012737:Sex Factors
chemical_list: D015415:Biomarkers; D002097:C-Reactive Protein