title: Comparison of the possum, P-POSSUM and Cr-POSSUM scoring systems as predictors of postoperative mortality in patients undergoing major colorectal surgery.
abstract: BACKGROUND
  Physiologic and operative severity score for the enumeration of mortality and morbidity (POSSUM), 'Portsmouth'-physiologic and operative severity score for the enumeration of mortality and morbidity (P-POSSUM) and 'Colorectal'-physiologic and operative severity score for the enumeration of mortality and morbidity (Cr-POSSUM) are three related scoring systems, which uses individual patient parameters to predict postoperative mortality. POSSUM overpredicts mortality in low-risk patients and underpredicts mortality in elderly and emergency patients. P-POSSUM was developed to compensate for these weaknesses. Cr-POSSUM was developed specifically for colorectal surgery. We aim to establish which of these scoring systems would be most useful in an Australasian context.
  
  
  METHODS
  Data were collected for 308 patients and predicted mortality risk values were generated using each of the three systems. The Mann-Whitney U-test was then carried out on the scores for each system. Receiver-operator characteristic curves were designed to determine the relative accuracy of each approach at discriminating between death and survival.
  
  
  RESULTS
  All three POSSUM scoring systems showed a statistically significant ability to predict postoperative mortality. Additionally, in each system there was a significant difference in the raw physiologic and operative severity scores between survivors and those who died. A risk-stratification model was applied to each set of data, showing a correlation between an increase in risk and an increase in mortality rate. Finally, the receiver-operator characteristic curves generated showed that in this study group POSSUM, P-POSSUM and Cr-POSSUM were all satisfactory predictive tools although the latter tended to be relatively less accurate.
  
  
  CONCLUSIONS
  Physiologic and operative severity score for the enumeration of mortality and morbidity, P-POSSUM and Cr-POSSUM are all reliable predictors of postoperative mortality in the Australasian context; although there was a trend towards POSSUM and P-POSSUM being better predictors than Cr-POSSUM. However, Cr-POSSUM requires fewer individual patient parameters to be calculated and is thus easier to generate. An ideal preoperative scoring system remains to be developed for predicting mortality in patients undergoing colorectal surgery.
authors.affiliation: Department of Surgery, South Auckland Clinical School, University of Auckland, Otahuhu, Auckland, New Zealand.
authors.forename: Ryash
authors.initials: R
authors.lastname: Vather
authors.forename: Kamran
authors.initials: K
authors.lastname: Zargar-Shoshtari
authors.forename: Samuel
authors.initials: S
authors.lastname: Adegbola
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Hill
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003107:Colorectal Surgery / Q000401:mortality*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012372:ROC Curve; D012107:Research Design / Q000706:statistics & numerical data*; D012189:Retrospective Studies