title: POSSUM models in open abdominal aortic aneurysm surgery.
abstract: OBJECTIVE
  This study evaluated the Physiological and Operative Severity Score for the enUmeration of Mortality and Morbidity (POSSUM), Portsmouth (P) POSSUM and Vascular (V) POSSUM. The primary aim was to assess the validity of these scoring systems in a population of patients undergoing elective and emergency open AAA repair. The secondary intention was in the event that these equations did not fit all patients with an aneurysm; a new model would be developed and tested using logistic regression from the local data (Cambridge POSSUM).
  
  
  METHODS
  POSSUM data items were collected prospectively in a group of 452 patients undergoing elective and emergency open AAA repair over an eight-year period. The operative mortality rates were compared with those predicted by POSSUM, P-POSSUM, V-POSSUM and Cambridge POSSUM.
  
  
  RESULTS
  All models except V-POSSUM (physiology only) showed significant lack of fit when predicting mortality after open AAA surgery. It was found that the locally generated single unified model (Cambridge POSSUM) could successfully describe both elective and ruptured AAA mortality with good discrimination (chi(2)=9.24, 7 d.f., p=0.236, c-index=0.880).
  
  
  CONCLUSIONS
  POSSUM, V-POSSUM and P-POSSUM may not be robust tools for comparing mortality between populations undergoing elective and emergency open AAA repair as once thought. The development and successful validation of Cambridge POSSUM provides a unified model to describe both elective and emergency AAAs together and should be validated in other geographical settings.
authors.affiliation: Cambridge Vascular Unit, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK.
authors.forename: T Y
authors.initials: TY
authors.lastname: Tang
authors.forename: S R
authors.initials: SR
authors.lastname: Walsh
authors.forename: D R
authors.initials: DR
authors.lastname: Prytherch
authors.forename: C
authors.initials: C
authors.lastname: Wijewardena
authors.forename: M E
authors.initials: ME
authors.lastname: Gaunt
authors.forename: K
authors.initials: K
authors.lastname: Varty
authors.forename: J R
authors.initials: JR
authors.lastname: Boyle
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017542:Aneurysm, Ruptured / Q000401:mortality / Q000601:surgery; D017544:Aortic Aneurysm, Abdominal / Q000401:mortality* / Q000601:surgery; D017558:Elective Surgical Procedures; D004638:Emergency Treatment; D004739:England / Q000453:epidemiology; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D016015:Logistic Models; D008297:Male; D008485:Medical Audit; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011379:Prognosis; D011446:Prospective Studies; D012720:Severity of Illness Index; D016019:Survival Analysis