title: The complex relationship between pediatric cardiac surgical case volumes and mortality rates in a national clinical database.
abstract: OBJECTIVE
  We sought to determine the association between pediatric cardiac surgical volume and mortality using sophisticated case-mix adjustment and a national clinical database.
  
  
  METHODS
  Patients 18 years of age or less who had a cardiac operation between 2002 and 2006 were identified in the Society of Thoracic Surgeons Congenital Heart Surgery Database (32,413 patients from 48 programs). Programs were grouped by yearly pediatric cardiac surgical volume (small, <150; medium, 150-249; large, 250-349; and very large, >or=350 cases per year). Logistic regression was used to adjust mortality rates for volume, surgical case mix (Aristotle Basic Complexity and Risk Adjustment for Congenital Heart Surgery, Version 1 categories), patient risk factors, and year of operation.
  
  
  RESULTS
  With adjustment for patient-level risk factors and surgical case mix, there was an inverse relationship between overall surgical volume as a continuous variable and mortality (P = .002). When the data were displayed graphically, there appeared to be an inflection point between 200 and 300 cases per year. When volume was analyzed as a categorical variable, the relationship was most apparent for difficult operations (Aristotle technical difficulty component score, >3.0), for which mortality decreased from 14.8% (60/406) at small programs to 8.4% (157/1858) at very large programs (P = .02). The same was true for the subgroup of patients who underwent Norwood procedures (36.5% [23/63] vs 16.9% [81/479], P < .0001). After risk adjustment, all groups performed similarly for low-difficulty operations. Conversely, for difficult procedures, small programs performed significantly worse. For Norwood procedures, very large programs outperformed all other groups.
  
  
  CONCLUSIONS
  There was an inverse association between pediatric cardiac surgical volume and mortality that became increasingly important as case complexity increased. Although volume was not associated with mortality for low-complexity cases, lower-volume programs underperformed larger programs as case complexity increased.
authors.affiliation: Division of Cardiothoracic Surgery, Oregon Health and Science University, Portland, Ore. 97239-3098, USA. welkek@ohsu.edu
authors.forename: Karl F
authors.initials: KF
authors.lastname: Welke
authors.forename: Sean M
authors.initials: SM
authors.lastname: O'Brien
authors.forename: Eric D
authors.initials: ED
authors.lastname: Peterson
authors.forename: Ross M
authors.initials: RM
authors.lastname: Ungerleider
authors.forename: Marshall L
authors.initials: ML
authors.lastname: Jacobs
authors.forename: Jeffery P
authors.initials: JP
authors.lastname: Jacobs
mesh_terms: D000293:Adolescent; D006348:Cardiac Surgical Procedures / Q000379:methods / Q000401:mortality* / Q000706:statistics & numerical data; D002423:Cause of Death; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006330:Heart Defects, Congenital / Q000175:diagnosis / Q000401:mortality* / Q000601:surgery*; D017052:Hospital Mortality / Q000639:trends*; D006801:Humans; D007223:Infant; D016015:Logistic Models; D008297:Male; D015588:Observer Variation; D016017:Odds Ratio; D017063:Outcome Assessment, Health Care; D011336:Probability; D012042:Registries; D012189:Retrospective Studies; D020379:Risk Adjustment; D012720:Severity of Illness Index; D013503:Surgery Department, Hospital / Q000706:statistics & numerical data; D016019:Survival Analysis; D014481:United States; D016526:Workload / Q000706:statistics & numerical data*