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Is referral source a risk factor for coronary surgery? Health maintenance organization versus fee-for-service system
A Starr1, A P Furnary, G L Grunkemeier
1Albert Starr Academic Center for Cardiac Surgery, Providence Health System, Portland, OR, USA.
Insights
Health maintenance organization (HMO) patients had lower operative mortality for coronary artery bypass grafting compared to fee-for-service (FFS) patients. This difference was linked to the HMO
Area of Science:
- Cardiovascular Surgery
- Health Services Research
- Comparative Effectiveness
Background:
- Coronary artery bypass grafting (CABG) is a major surgical procedure.
- Health maintenance organizations (HMOs) and fee-for-service (FFS) models represent different healthcare delivery systems.
- Previous outcomes data comparing CABG in HMO versus FFS settings is limited.
Purpose of the Study:
- To compare operative mortality rates for CABG between patients in an HMO and those in an FFS system.
- To identify factors contributing to observed differences in outcomes.
- To evaluate the impact of healthcare system structure on surgical outcomes.
Main Methods:
- Retrospective analysis of 8483 CABG operations performed between 1974 and an unspecified end date.
- Comparison of patient outcomes between an HMO group (3168 operations) and an FFS group (5315 operations).
- Univariate and multivariable logistic regression analyses to identify risk factors for operative mortality.
Main Results:
- Overall operative mortality was significantly lower in the HMO group (2.7%) compared to the FFS group (4.6%) (p=0.00002).
- Multivariable analysis identified seven independent risk factors for operative mortality, with the FFS group variable approaching significance.
- The HMO system exhibited a lower angioplasty/coronary bypass ratio (0.6 vs. 1.5), suggesting less aggressive revascularization strategies.
Conclusions:
- The HMO system, characterized by multidisciplinary screening and absence of financial incentives for self-referral, was associated with lower CABG operative mortality.
- Systemic factors within the HMO, including a robust selection process leading to fewer emergencies and redo operations, contributed to improved outcomes.
- The coordinated structure of a mature HMO may yield better cardiovascular management outcomes than a non-coordinated FFS system.
Abstract:
We began performing coronary artery bypass grafting for a large health maintenance organization (HMO) in 1974, as the sole provider of their cardiac surgery. The outcomes of our HMO group of patients were compared with those of our patients treated on a fee-for-service (FFS) basis. The HMO system entails preintervention and multidisciplinary screening conferences and is devoid of self-referral and personal financial incentives. Since 1985, the operative mortality for HMO patients has been consistently lower than for FFS patients. There were 8483 operations during this study period: 3168 (37%) were in the HMO group, with an overall operative mortality of 2.7%, and 5315 (63%) were in the FFS group, with an operative mortality of 4.6% (p=0.00002). This difference was investigated with univariate and multivariable analyses. Sixteen factors were found to univariately affect the risk of operative mortality; for five of these risk correlates there was a significant maldistribution between the HMO and FFS patients. Logistic regression was used to explore the influence of this imbalance in risk factors. The model found seven independent risk factors (left ventricular failure, emergency coronary bypass, redo bypass, nonuse of the internal thoracic artery, unstable angina, age, and diabetes) that significantly affected operative mortality. The FFS group variable closely approached independent risk significance at p=0.059. This multivariable model explained only one third of the observed differences in actual mortality between the HMO and FFS groups. The system-wide angioplasty/coronary bypass ratio, which could not be used in a patient-specific model, was 0.6 in the HMO system and 1.5 in the FFS group. Other factors related to the operating structure of a mature, large HMO may account for the remainder of the difference. The HMO referral system, through a powerful selection process, resulted in fewer emergencies, redo bypass operations, and catheterization complications that, in turn, yielded lower operative mortality than a noncoordinated FFS system of cardiovascular management.