Physiologic and Operative Severity Score for the Enumeration of Mortality and Morbidity (POSSUM)
The POSSUM system combines medical risk status with a score for the magnitude of the surgical intervention. It is a 12 point physiologic and 6 point operative scoring system. It uses an exponential method of regression analysis. The Portsmouth modification (P_POSSUM) was developed to predict mortality more closely by using a linear method rather than the exponential method of regression analysis
On the basis of the methods used by POSSUM and P-POSSUM, the CR-POSSUM was developed for colorectal surgery and the O-POSSUM, specific for esophageal and gastric surgery