title: Effect of endovascular aneurysm repair on the volume-outcome relationship in aneurysm repair.
abstract: BACKGROUND
  We aim to quantify the relationship between the annual caseload (volume) and outcome from elective endovascular (EVR) or open repair of abdominal aortic aneurysms (AAAs) in England between 2005 and 2007.
  
  
  RESULTS
  Individual patient data were obtained from the Hospital Episode Statistics. Statistical methods included multiple logistic regression models, mortality control charts, and safety plots to determine the nature of any relationship between volume and outcome. The case-mix between hospitals of different sizes was examined using observed and expected values for in-hospital mortality. Outcome measures included in-hospital mortality and hospital length of stay. Between 2005 and 2007, a total of 57 587 patients were admitted to hospitals in England with a diagnosis of AAA, and 11 574 underwent AAA repair. There were 7313 elective AAA repairs, of which 5668 (78%) were open and 1645 (22%) were EVR. In-hospital mortality rates were 5.63% for all elective AAA repairs with rates of 6.18% for open repair and 3.77% for EVR (odds ratio, 0.676; 95% CI, 0.501 to 0.913; P=0.011). High-volume aneurysm services were associated with significantly lower mortality rates overall (0.991; 0.988 to 0.994; P<0.0001), for open repairs (0.994; 0.991 to 0.998; P=0.0008), and EVR (0.989; 0.982 to 0.995; P=0.0007). Large endovascular units had low mortality rates for open repairs.
  
  
  CONCLUSIONS
  A strong relationship existed between the volume of surgery performed and outcome from both open and endovascular aneurysm repairs. These data support the concept that abdominal aortic surgery should be performed in specialized units that meet a minimum volume threshold.
authors.affiliation: Department of Outcomes Research, St George's Vascular Institute, London; and Community Health Sciences, St George's University of London, United Kingdom. pholt@sgul.ac.uk
authors.forename: Peter J E
authors.initials: PJ
authors.lastname: Holt
authors.forename: Jan D
authors.initials: JD
authors.lastname: Poloniecki
authors.forename: Usman
authors.initials: U
authors.lastname: Khalid
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Hinchliffe
authors.forename: Ian M
authors.initials: IM
authors.lastname: Loftus
authors.forename: Matt M
authors.initials: MM
authors.lastname: Thompson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D017544:Aortic Aneurysm, Abdominal / Q000401:mortality / Q000601:surgery*; D001019:Aortic Rupture / Q000401:mortality / Q000601:surgery; D003953:Diagnosis-Related Groups; D017558:Elective Surgical Procedures; D004739:England / Q000453:epidemiology; D005260:Female; D017052:Hospital Mortality; D006761:Hospitals / Q000706:statistics & numerical data; D006801:Humans; D007902:Length of Stay; D016015:Logistic Models; D008297:Male; D017063:Outcome Assessment, Health Care; D011787:Quality of Health Care; D012307:Risk Factors; D014656:Vascular Surgical Procedures / Q000706:statistics & numerical data*