Variation in Volume-Outcome
Relationships for Hospitals and
Surgeons Performing CABG Surgery
Christopher P. Gorton MD, MHSA
Jayne L. Jones MPH
Christopher S. Hollenbeak PhD
David B. Campbell MD
Diane L. Arke MS
Pennsylvania Health Care Cost Containment Council

Research Objectives:

To describe the variation in risk-adjusted outcomes for individual surgeons and hospitals with similar case volumes

To examine the association between case volume and two outcomes, 30-day mortality rates and 7-day readmission rates, for surgeons and hospitals
Pennsylvania Health Care Cost Containment Council

Methods
Isolated CABG surgeries, 2002:
16,435 patients; 62 non-federal Pennsylvania hospitals; 190 surgeons
Retrospective analysis of administrative and medical record abstracted data reflecting statewide experience. Generalized estimating equations (GEE) framework used to account for the correlations between patients treated by the same surgeons and at the same hospital.
Pennsylvania Health Care Cost Containment Council

Principal Findings

Wide variation was seen between and within outcome measures at all volume levels

Extreme mortality observations were demonstrated across the entire volume spectrum.

Likelihood of patient death within thirty days decreased as surgeon case volume increased
(adjusted risk ratio [RR] for each 25 case increment, 0.93; 95% confidence interval [CI],
0.87-0.99; P=0.031).
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Regression Coefficients
Outcome Measure
Hospital Case Volume Surgeon Case Volume
Model Parameters
Initial
Model
30-day
Mortality
7-day
Readmission
30-day
Mortality
7-day
Readmission
Coefficient -0.001 0.000 -0.003 -0.002 p-value 0.0706 0.3099 0.0314 0.0967
Revised
Model
Coefficient -0.001 p-value 0.0708
0.000
0.3047
-0.004
0.0045
-0.002
0.0424
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Hospital Annual CABG Volume, No. of Procedures
0 50 100 150 200
Surgeon Annual CABG Volume, No. of Procedures
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Results of Simulated Policy of Referral to Mid-High Volume Surgeons

Modeled outcomes of 1,000 simulated choices in each of 8 regions, in which patients of low volume surgeons were reassigned to surgeons with mid-high volumes in the same region

Statewide Mortality Risk Ratio, Observed vs.
Simulation: 1.080 (95% CI: 0.927 to 1.260)

With selective referral, predicted lives saved =
23, but 15.9% probability of increased lives lost
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Surgeon Mortality:
Actual vs. Simulated
All Surgeons High Volume Surgeons
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Probability Distribution of Predicted
Lives Saved by Simulated Policy
-100 -50 0 50
Predicted Lives Saved
100 150
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Conclusions

For individual consumers, surgeon volume is a weak predictor of mortality and re-admission

Large scale implementation of a selective CABG referral policy has non-trivial probability of negative public health impact

Lack of correlation among four studied outcome measures highlights need for multi-dimensional performance measurement
Pennsylvania Health Care Cost Containment Council