Evaluation of the P-POSSUM mortality prediction algorithm in Australian surgical intensive care unit patients

The Physiological and Operative Severity Score for enUmeration of Mortality and Morbidity (POSSUM) is an auditing tool designed to compare surgical outcomes independent of case mix. It uses patient physiological and operative data to predict morbidity and mortality for surgical patients. Thus far most evaluations of the POSSUM algorithm and its modifications have emanated from British hospitals. A single-centre retrospective study was therefore performed to determine the applicability of this tool to the Australian surgical case mix.

All surgical patients undergoing a surgical procedure admitted to the Royal Brisbane Hospital intensive care facility in 1999 were reviewed retrospectively. Mortality predictions using the Portsmouth modification of the POSSUM algorithm (P--POSSUM) were compared to the actual outcomes using receiver-operator characteristic curve analysis and the Hosmer and Lemeshow Goodness-of-Fit test.

The records of 229 admissions were reviewed. The area under the receiver-operator characteristic curve was 0.68, significantly greater than 0.5 (P = 0.014). Predicted deaths were significantly greater than actual deaths (50 vs 28, P < 0.001), with over-prediction of death rates in all mortality groupings except the two lowest risk deciles.

The P-POSSUM algorithm tends to over-estimate mortality in surgical intensive care patients. It may require further calibration before adoption as a surgical audit tool in Australia.