The Relationship Between Volume and Outcome Following Elective Open Repair of Abdominal Aortic Aneurysms (AAA) in 131 German Hospitals

Objectives: Several studies indicate that high-volume hospitals have better results in open repair of unruptured abdominal aortic aneurysms (AAA). Up to now no studies had addressed this question in German hospitals. Design: Post-hoc-analysis from a prospective physician-led registry. Material and methods: Since 1999, the German Society for Vascular Surgery has conducted a prospective registry for open and endovascular repair of AAAs. This study includes 131 hospitals who conducted n = 10163 elective open repairs for unruptured AAA between 1999 to 2004. All perioperative variables including annual volume as a continuous variable were analysed in a step-wise logistic regression model. In order to define a threshold annual volume an additional logistic regression analysis was performed by use of annual volume groups (0-9, 10-19, 20-29, 30-39, 40-49, 50 or more). The relationship between annual volume and further outcome parameters (length of procedure, blood transfusion, length of stay) were also analyzed. Results: The overall mortality rate was 3.2%. The stepwise logistic regression model identified the following predictors of an increased perioperative mortality: age (OR 1.084, 95% CI 1.066-1.102), AAA diameter (OR 1.008, 95% CI 1.001-1.016), length of procedure (OR 1.008, 95% CI 1.006-1.009), ASA-Score (OR 2.636, 95% CI 2.129-3.264), suprarenal clamping (OR 1.447, 95% CI 1.008-2,078), blood transfusion (OR 1.786, 95% CI 1.268-2.514). Annual volume was moderately predictive (OR 1.003, 95% CI 1-1.006) but failed to reach statistical significance (p = 0.07). The analysis of volume groups identified a significantly higher risk for hospitals with an annual volume of 1-9 AAA-repairs by comparison to hospitals with an annual volume of 50 or more AAA-repairs (OR 1.903, 95% CI 1.124-3.222). Operations at low volume hospitals were also longer (p < 0.001), with an extended postoperative stay (p < 0.001) and a higher transfusion rate (p < 0.001). Conclusions: Patient's age, ASA classification, AAA diameter, length of procedure, suprarenal clamping and blood transfusion are predictive variables for an increased perioperative mortality in elective open AAA repair. Mortality is also increased by a low annual volume. Further studies are needed to examine whether these data are applicable to all German hospitals.