POSSUM AND PORTSMOUTH POSSUM FOR PREDICTING MORTALITY

Background There is a need for an accurate measure of surgical outcome s so that hospitals and surgeons can be compared properly regardless o f case mix. POSSUM (Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity) uses a physiological score an d an operative severity score to calculate risks of mortality and morb idity. In a previous small study it was found that Portsmouth POSSUM ( P-POSSUM; a modification of the POSSUM system) provided a more accurat e prediction of mortality. Methods Some 10 000 general surgical interv entions (excluding paediatric and day cases) were studied prospectivel y between August 1993 and November 1995. The POSSUM mortality equation was applied to the full 10 000 surgical episodes. The 10 000 patients were arranged in chronological order and the first 2500 were used as a training set to produce the modified P-POSSUM predictor equation. Th is was then applied prospectively to the remaining 7500 patients arran ged chronologically in five groups of 1500. Results The original POSSU M logistic regression equation for mortality overpredicts the overall risk of death by more than twofold and the risk of death for patients at lowest risk (5 per cent or less) by more than sevenfold. The P-POSS UM equation produced a very close fit with the observed in-hospital mo rtality. Conclusion P-POSSUM provides an accurate method for comparati ve surgical audit.