National risk prediction model for elective abdominal aortic aneurysm repair

Background Mortality results for elective abdominal aortic aneurysm (AAA) repair are published by the Vascular Society of Great Britain and Ireland. These mortality results are not currently risk-adjusted. The objective of this study was to develop a national risk prediction model for elective AAA repair. Methods Data for consecutive patients undergoing elective AAA repair from the National Vascular Database between April 2008 and March 2011 were analysed. Multiple logistic regression and backwards model selection were used for model development. The study outcome measure was in-hospital mortality. Model calibration and discrimination were assessed for all AAA repairs, and separately for open repair and endovascular aneurysm repair (EVAR) subgroups. Results There were 312 in-hospital deaths among 11 423 AAA repairs (2 center dot 7 (95 per cent confidence interval (c.i.) 2 center dot 4 to 3 center dot 0) per cent): 230 after 4940 open AAA repairs (4 center dot 7 (4 center dot 1 to 5 center dot 3) per cent) and 82 after 6483 EVARs (1 center dot 3 (1 center dot 0 to 1 center dot 6) per cent). Variables associated with in-hospital death included in the final model were: open repair, increasing age, female sex, serum creatinine level over 120 mu mol/l, cardiac disease, abnormal electrocardiogram, previous aortic surgery or stent, abnormal white cell count, abnormal serum sodium level, AAA diameter and American Society of Anesthesiologists fitness grade. The area under the receiver operating characteristic (ROC) curve was 0 center dot 781 (95 per cent c.i. 0 center dot 756 to 0 center dot 806) with a bias-corrected value of 0 center dot 774. Model calibration was good (P = 0 center dot 963) based on the HosmerLemeshow goodness-of-fit test, (bias-corrected) calibration curves, risk group assessment and recalibration regression. Conclusion This multivariable model for elective AAA repair can be used to risk-adjust outcome analyses and provide patient-specific estimates of in-hospital mortality risk for open AAA repair or EVAR.