POSSUM and P-POSSUM overpredict mortality for carotid endarterectomy

Objectives: the aim was to test the predictive accuracy of POSSUM and P-POSSUM on patients undergoing CEA. Design: retrospective and prospective study. Materials: 499 CEAs performed by four vascular surgeons from a single unit from 1992-99. The median age was 68 (range 38-86) and 60% were men. Methods: physiological parameters, operative parameters and the 30-day mortality were collected. Predicted mortality for each patient was calculated using POSSUM and P-POSSUM equations. Patients were stratified into risk groups and observed and predicted deaths were compared. Accuracy of the prediction was assessed using chi-squared analysis. Results: the observed 30-day mortality was 1.8% (9/499). The predicted deaths using POSSUM and P-POSSUM analysis were 49 and 25 respectively compared to nine observed deaths. There was significant evidence of lack of fit of both models in predicting mortality (chi-squared analysis, p<0.05). Conclusions: POSSUM and P-POSSUM overpredict mortality and are unsuitable for comparative audit of CEA. Models developed specific for CEA might accurately predict mortality.