The Norwood operation: Relative effects of surgeon and institutional volumes on outcomes and resource utilization

Abstract

Background: Hypoplastic left heart syndrome is the most expensive birth defect managed in the United States, with a 5-year survival rate below 70%. Increasing evidence suggests that hospital volumes are inversely associated with mortality for infants with single ventricles undergoing stage 1 surgical palliation. Our aim was to examine the relative effects of surgeon and institutional volumes on outcomes and resource utilisation for these children.

Methods: A retrospective study was conducted using the Pediatric Health Information System database to examine the effects of the number of procedures performed per surgeon and per centre on mortality, costs, and post-operative length of stay for infants undergoing Risk Adjustment for Congenital Heart Surgery risk category six operations at tertiary-care paediatric hospitals, from 1 January, 2004 to 31 December, 2013. Multivariable modelling was used, adjusting for patient and institutional characteristics. Gaussian kernel densities were constructed to show the relative distributions of the effects of individual institutions and surgeons, before and after adjusting for the number of cases performed.

Results: A total of 2880 infants from 35 institutions met the inclusion criteria. Mortality was 15.0%. Median post-operative length of stay was 24 days (IQR 14-41). Median standardized inpatient hospital costs were $156,000 (IQR $108,000-$248,000) in 2013 dollars. In the multivariable analyses, higher institutional volume was inversely associated with mortality (p=0.001), post-operative length of stay (p=0.004), and costs (p=0.001). Surgeon volume was associated with none of the measured outcomes. Neither institutional nor surgeon volumes explained much of the wide variation in outcomes and resource utilization observed between institutions and between surgeons.

Conclusions: Increased institutional - but not surgeon - volumes are associated with reduced mortality, post-operative length of stay, and costs for infants undergoing stage 1 palliation.

Keywords: Hypoplastic left heart syndrome; Norwood; costs; outcomes; surgeon volume.

Figure 1. The Effects of Volumes on the Variation in Mortality between Institutions and between Surgeons

Kernel density plots graphically display differences in the distribution of hospital (Fig. 1a) and surgeon (Fig. 1b) fixed effects on mortality for infants undergoing stage 1 palliation. Blue lines show the distribution of fixed effects before adjusting multivariable models for institutional or surgeon volumes. Red lines show the distribution of fixed effects before adjusting multivariable models for institutional or surgeon volumes. Neither the variation between institutions nor the variation between surgeons changed substantially after adjusting for volumes.

Figure 2. The Effects of Volumes on the Variation in Postoperative Length of stay between Institutions and between Surgeons

Kernel density plots graphically display differences in the distribution of hospital (Fig. 2a) and surgeon (Fig. 2b) fixed effects on postoperative length of stay for infants undergoing stage 1 palliation. Blue lines show the distribution of fixed effects before adjusting multivariable models for institutional or surgeon volumes. Red lines show the distribution of fixed effects before adjusting multivariable models for institutional or surgeon volumes. Neither the variation between institutions nor the variation between surgeons changed substantially after adjusting for volumes.

Figure 3. The Effects of Volumes on the Variation in Total Inpatient Hospital Costs between Institutions and between Surgeons

Kernel density plots graphically display differences in the distribution of hospital (Fig. 3a) and surgeon (Fig. 3b) fixed effects on costs for infants undergoing stage 1 palliation. Blue lines show the distribution of fixed effects before adjusting multivariable models for institutional or surgeon volumes. Red lines show the distribution of fixed effects before adjusting multivariable models for institutional or surgeon volumes. Neither the variation between institutions nor the variation between surgeons changed substantially after adjusting for volumes.