Surgeon intuition is inferior to a simple web-based risk calculator for predicting anastomotic leak. Tarik Sammour, Mark Lewis, Michelle L Thomas, Matt J Lawrence, Andrew Hunter, James W Moore

This is day 6 after an extended right hemicolectomy…and it’s every surgeon’s nightmare. In day to day practice, leak rates quoted to patients are often based on average leak rates across a population or perhaps a single surgeons experience, and individualised risk assessments are not in common use. This is despite the fact that there have been numerous published studies that have identified independent risk factors for anastomotic leak

In 2014 an excellent prospective study in over 3000 patients was published looked at 42 variables that could predict leaks, of which 6 were found to be independently predictive. These authors also worked out a nomogram that could be applied to patients. The problem was the format of the nomogram was archaic. I mean seriously who has the time to bust out a ruler to work this out for each patients? So we fixed that…

Aim Prospectively validate risk calculator on local cohort Compare predictive its predictive value with the risk assessment of the primary surgeon. Aim of this study was to prospectively validate this nomogram for the first time on an external data set and compare its predictive value with the estimate of the primary operating surgeon.

Methods Prospective data collection for one year. Elective and emergency colon cancer resections Exclusions: R2 resection Rectal cancer (15cm from anal verge) Stoma formation Benign disease Primary outcome defined: Anastomotic leak ROC curve analysis of online calculator vs surgeons’ estimate Anastomotic leak was defined as: “leak of luminal contents from a surgical join between diagnosed by any of the following methods: Radiologically, by a radiographic enema with hydrosoluble contrast or by computerized tomography (CT) with presence of intraabdominal collection adjacent to the anastomosis. Clinically, with evidence of extravasation of bowel content or gas through a wound or drain. Endoscopy. Intraoperatively. Any anastomotic leak by the above definition that was treated with antibiotics, drainage (radiological or otherwise), or reoperation was considered clinically important

152 colectomies

Results Anastomotic leak rate 9.6% (8 patients) 4 Antibiotics only 3 Percutaneous drainage 1 Return to OT and anastomosis taken down (died) All had prolonged intravenous antibiotics Median hospital stay 14 days Four of these after elective right hemicolectomy, one after emergency right hemicolectomy, two after elective high anterior resection and one after emergency subtotal colectomy. Post hoc power calculation for the ROC analysis (accounting for an AUROC of 0.84 and a leak rate of 9.6%) confirms that the current sample size is adequately powered for an alpha (Type I error) of 0.05 and a beta (Type II error) of 0.9.

Death leak and the other high grade SBO and requested palliation

ROC = 0.84 P < 0.002* The statistical optimal cut-off value for the calculator estimate was 11% Likelihood ratio 3.45 Sensitivity 0.88 Specificity 0.75 PPV 0.27 NPV 0.98 ROC = 0.40 P = 0.243 Youden’s index

Conclusion A simple anastomotic leak risk calculator is significantly better at predicting anastomotic leak than the estimate of the primary surgeon. Further external validation on a larger data set is required. The current study is the only study to date which directly compares surgeons’ intuition with a risk calculator for anastomotic leak, and is the first study to externally validate the nomogram derived by Frasson et al. and demonstrate its value over and above baseline clinical assessment. The strengths of this study include the prospective design, the blinded nature of the primary surgeons’ assessment, and completeness of data collection and follow-up.