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

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.

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.

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.

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.