POSSUM and P-POSSUM for risk-adjusted audit of patients undergoing emergency laparotomy

BACKGROUND: The Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity (POSSUM) is a scoring system that is used widely to predict 30-day mortality and morbidity rates. The Portsmouth predictor modification (P-POSSUM) was developed to overcome the overprediction of mortality by POSSUM, especially in low-risk patients. In this prospective study, the validity of POSSUM and P-POSSUM was tested in patients undergoing emergency laparotomy in a referral hospital of a developing country. METHODS: Some 120 patients who underwent emergency laparotomy in a single unit were studied. Predicted morbidity and mortality rates were calculated by POSSUM and P-POSSUM equations using both linear regression and the exponential methods of analysis. These were compared with actual outcomes. RESULTS: When the linear method of analysis was used POSSUM overpredicted morbidity, and there was a significant difference between the observed and predicted values (observed to expected (O : E) ratio 0.68). The prediction was more accurate when the exponential method was used (O : E ratio 0.91). POSSUM also significantly overpredicted mortality when analysed by the linear method (O : E ratio 0.39), but the prediction improved when exponential analysis was used (O : E ratio 0.62). Applying linear and exponential analyses for P-POSSUM, the O : E ratios for mortality were 0.66 and 0.88 respectively. CONCLUSION: If analysed correctly POSSUM is a good predictor of morbidity and mortality in patients undergoing emergency laparotomy. P-POSSUM predicts mortality equally well. Both equations may be used for risk-adjusted surgical audit of patients undergoing emergency laparotomy.