Portsmouth POSSUM models for abdominal aortic aneurysm surgery

Background: The Portsmouth Physiological and Operative Severity Score for e nUmeration of Mortality and morbidity (P-POSSUM) equation permits comparati ve audit that allows for differences in case mix. The methodology has previ ously been shown accurately to model general surgical and vascular surgical patients. Patients with a ruptured abdominal aortic aneurysm (AAA) are, ho wever, very different from elective patients and it may be hypothesized tha t they require their own specific risk model. Methods: POSSUM data on 444 (213 emergency, 231 elective) admissions for AA A surgery between August 1993 and July 2000 were analysed using the P-POSSU M equation for general surgery and the P-POSSUM equations developed for vas cular surgery. Results: All equations successfully modelled the elective aneurysms but fai led to fit the emergency aneurysms, and the elective and emergency aneurysm s combined. This suggested that admission method (not a POSSUM data item) i s an important factor for patients with AAA. However, with these data it wa s not possible to generate a model, including admission method, that succes sfully modelled the combined elective and emergency data. The 213 emergency aneurysm repairs were divided into two groups by operation date. The first 106 (training set) were used to form logistic regression models following the P-POSSUM methodology. These models were found successfully to fit the r emaining 107 records (test set) on prospective application (chi (2) = 4.50, 4 d.f., P = 0.345). Conclusion: Ruptured AAAs appear to be different from elective AAAs and oth er vascular cases and require their own risk model.