Surgical Outcome Risk Tool (SORT) to predict 30-day postoperative mortality in a mixed surgical population in Swedish tertiary hospitals

BACKGROUND: The Surgical Outcome Risk Tool (SORT) was derived and validated in the UK to improve preoperative prediction of postoperative risk. The aim of this study was to validate the SORT in a European mixed-case surgical population outside of the UK. METHODS: The study included patients aged at least 18 years with ASA Physical Status (ASA-PS) grades I–V who underwent non-cardiac surgery at four tertiary hospitals in Sweden between November 2015 and February 2016. Exclusion criteria were surgery under local anaesthesia and missing data on the SORT predictors (ASA-PS, surgical urgency, high-risk surgery, surgical severity, malignancy, age over 65 years). The outcome was 30-day mortality. Discrimination and calibration of the SORT were assessed using area under the receiver operating curve (AUROC) statistics and calibration plots. A sensitivity analysis was done in a high-risk subgroup (ASA-PS III or higher; surgical complexity major to Xmajor according to the SORT; gastrointestinal, orthopaedic, urogenital/obstetric surgery; and age at least 18 years). RESULTS: The validation cohort included 17 965 patients; median age was 58 (i.q.r. 40–70) years, 43.2 per cent were men, and the mortality rate at 30 days was 1.6 per cent. The SORT had excellent discrimination, with an AUROC of 0.91 (95 per cent c.i. 0.89 to 0.92), and good calibration. The high-risk subgroup (1807 patients) had a 30-day mortality rate of 5.6 per cent; in the sensitivity analysis, the SORT had good discrimination, with an AUROC of 0.79 (0.74 to 0.83), and calibration remained good. CONCLUSION: The estimates of the original the SORT for prediction of 30-day mortality were valid and reliable in a mixed-case surgical population in a non-UK European setting.