The complex relationship between center volume and outcome in patients undergoing the Norwood operation.
BACKGROUND
Norwood outcomes vary across centers, and a relationship between center volume and outcome has been previously described. It is unclear whether this volume-outcome relationship exists across all levels of patient risk or holds true for all centers. We evaluated the impact of patient risk status on the relationship between center volume and outcome, and the extent to which differences in center volume account for between-center variation in outcome.


METHODS
Infants in The Society of Thoracic Surgeons Congenital Heart Surgery Database undergoing the Norwood operation (2000 to 2009) were included. Mortality associated with annual Norwood volume overall and across patient preoperative risk tertiles was evaluated in multivariable analysis. We also estimated the proportion of between-center variation in mortality explained by center volume.


RESULTS
The cohort included 2,557 infants from 53 centers: 34 centers with 0 to 10 Norwood cases per year; 13 centers with 11 to 20 cases per year; and 6 centers with more than 20 cases per year. Unadjusted in-hospital mortality was 22%. In multivariable analysis, lower center volume was associated with higher mortality (odds ratio in low-volume versus high-volume centers 1.54, 95% confidence interval: 1.02 to 2.32, p=0.04). The volume-outcome relationship did not differ across preoperative risk tertiles (p=0.7). Norwood volume explained an estimated 14% of the between-center variation in mortality observed, and significant between-center variation in mortality remained after adjusting for volume (p<0.001).


CONCLUSIONS
Center volume is modestly associated with outcome after the Norwood operation independent of patient risk status. However, this relationship explains only a portion of the between-center variation in mortality in this cohort.
Department of Pediatrics, Duke University School of Medicine, Duke Clinical Research Institute, Durham, North Carolina 27715, USA. sara.pasquali@duke.edu
Sara K
SK
Pasquali
Jeffrey P
JP
Jacobs
Xia
X
He
Christoph P
CP
Hornik
Robert D B
RD
Jaquiss
Marshall L
ML
Jacobs
Sean M
SM
O'Brien
Eric D
ED
Peterson
Jennifer S
JS
Li
D002423:Cause of Death; D015331:Cohort Studies; D016001:Confidence Intervals; D016208:Databases, Factual; D004502:Education, Medical, Continuing; D005260:Female; D005500:Follow-Up Studies; D006330:Heart Defects, Congenital / Q000175:diagnosis / Q000401:mortality / Q000601:surgery*; D017052:Hospital Mortality / Q000639:trends*; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D008297:Male; D058327:Norwood Procedures / Q000009:adverse effects / Q000379:methods / Q000401:mortality*; D016017:Odds Ratio; D011183:Postoperative Complications / Q000401:mortality / Q000503:physiopathology; D012189:Retrospective Studies; D018570:Risk Assessment; D016019:Survival Analysis; D016896:Treatment Outcome; D016526:Workload / Q000706:statistics & numerical data*