Comparison of POSSUM and P-POSSUM as Audit Tools in Patients Undergoing Emergency Laparotomy for Secondary Bacterial Peritonitis

Abstract

Background : Though POSSUM and P-POSSUM have been proposed as accurate tools of audit, our initial experience has not been encouraging. Therefore, a prospective study was conducted to find their accuracy for predicting outcome in peritonitis patients who underwent emergency laparotomy. Methods : 172 patients treated in single surgical unit over two years were included. Expected morbidity and mortality, computed by POSSUM and P-POSSUM equations using linear as well as exponential methods of analysis, were compared with observed outcome by observed: expected (O:E) ratios. X2-test was done to draw statistical significance; Plt;0.050 was taken as significant. Results : POSSUM significantly over-predicted mortality with linear as well as exponential methods with O:E ratios being 0.32 (X2=57.35, 1 d.f. Plt;0.001) and 0.25 (X2=111.26, 1 d.f. Plt;0.001), respectively. P-POSSUM also significantly over-predicted mortality by linear as well as exponential methods with O:E ratios being 0.55 (X2=11.37, 1 d.f. Plt;0.001) and 0.27 (X2=92.30, 1 d.f. Plt;0.001), respectively. POSSUM significantly over-predicted morbidity by linear and exponential analysis with O:E being 0.76 (X2=47.94, 1 d.f. Plt;0.001) and 0.81 (X2=23.27, 1 d.f. Plt;0.001), respectively. Conclusions : Neither POSSUM nor P-POSSUM was found accurate for predicting the outcome by linear or exponential methods. Further studies are required to find their suitability for audit purposes in conditions prevailing in third world countries.