AN EVALUATION OF THE POSSUM SURGICAL SCORING SYSTEM

POSSUM (Physiological and Operative Severity Score for the enUmeration of Morbidity and mortality) has been studied as a possible surgical a udit system for a 9-month interval using a sample of 28 per cent of th e general surgical workload, Mortality or survival was analysed as an endpoint. Ira this sample the published POSSUM predictor equation for mortality overpredicted deaths by a factor of more than two, The bulk of the overpredict lon occurred in the group aii lowest risk (predicte d mortality 10 per cent Oh less), in which death was overpredicted by a factor of six. This is the most important group for audit purposes s ince it contains the majority of surgical patients and is composed of fit patients undergoing minor surgery The published predictor equation for mortality returns a minimum predicted mortality of 1.08 per cent, clearly far higher than that expected Tor a fit patient having minor surgery, Logistic regression was done on a set of 1485 surgical episod es to generate a local predictor equation for mortality. This process gave a predictor equation that fitted well with the observed mortality rate and gave a minimum predicted risk of mortality of 0.20 per cent, The previously published POSSUM predictor equation for mortality perf ormed badly when tested using a standard test of goodness of fit for l ogistic regression and must be modified.