Internal comparative audit in a thoracic surgery unit using the physiological and operative severity score for the enumeration of mortality and morbidity (POSSUM)

Objective: The aim of the study was to use the physiological and operative severity score for the enumeration of mortality and morbidity (POSSUM) to a ssess the performance of our thoracic surgery unit during two successive pe riods of activity. Methods: From 1992 through 1997, 801 candidates for thor acic procedures at our institution were considered fur the study. After val idation of the logistic regression model, including the POSSUM score, obser ved and POSSUM-predicted morbidities were compared within two groups Of pat ients divided by year of operation (group 1: 1992-1994, n = 362; group 2: 1 995-1997, n = 439) by means of the z-test for the comparison of a proportio n with an expected value. Results: The POSSUM-predicted morbidity was signi ficantly lower than the observed one in the first period of activity of our unit (19.6 vs. 24.3%, respectively; z-test for the comparison of a proport ion with an expected value, 2.25: P = 0.01), whereas no difference was foun d in the second period (20.5 vs. 19.1%, respectively: z-test for the compar ison of a proportion with an expected value, -0.71; P = 0.76). Conclusions: The result suggests a worse-than-expected performance of our unit in the f irst period of activity, showing that POSSUM can be reliably applied as an instrument of internal comparative audit in a thoracic surgery unit. (C) 20 01 Elsevier Science B.V. All rights reserved.