External validation of the Surgical Outcome Risk Tool (SORT) in 3305 abdominal surgery patients in the independent sector in the UK

Background Assessing the risk of post-surgical mortality is a key component of pre-surgical planning. The Surgical Outcome Risk Tool (SORT) uses pre-operative variables to predict 30-day mortality. The aim of this study was to externally validate SORT in patients undergoing major abdominal surgery. Methods Data were collected from patients treated in five independent hospitals in the UK. Individualised SORT scores were calculated, and area under the receiver operating characteristic (AUROC) and precision-recall curves (PRC) plus 95% confidence intervals (CI) were drawn to test the ability of SORT to identify in-hospital death. Outcomes of patients with a SORT predicted risk of mortality of ≥ 5% (high risk) were compared to those with a predicted risk of < 5% (standard risk). Results The study population comprised 3305 patients, mean age 51 years, 2783 (84.2%) underwent elective surgery most frequently involving the colon (24.6%), or liver, pancreas or gallbladder (18.2%). Overall, 1551 (46.9%) patients were admitted to ICU and 29 (0.88%) died. The AUROC of SORT for discriminating patients at risk of death in hospital was 0.899 (95% CI 0.849 to 0.949) and the PRC 0.247. In total, 72 (2.18%) patients were stratified as high risk. There were more unplanned ICU admissions and deaths in this group compared to the standard risk group (25.0% and 3.3%, versus 3.1% and 0.5%, respectively). Conclusion We externally validated SORT in a large population of abdominal surgery patients. SORT performed well in patients with lower risk profiles, but underpredicted adverse outcomes in the higher risk group.