IS REFERRAL SOURCE A RISK FACTOR FOR CORONARY SURGERY - HEALTH MAINTENANCE ORGANIZATION VERSUS FEE-FOR-SERVICE SYSTEM

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 compa red with those of our patients treated on a fee-for-service (FFS) basi s. The HMO system entails preintervention and multidisciplinary screen ing conferences and is devoid of self-referral and personal financial incentives, Since 1985, the operative mortality for HMO patients has b een consistently lower than for FFS patients. There were 8483 operatio ns 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 g roup, with an operative mortality of 4.6% (p = 0.00002). This differen ce was investigated with univariate and multivariable analyses. Sixtee n factors were found to univariately affect the risk of operative mort ality; for five of these risk correlates there mas a significant maldi stribution between the HMO and FFS patients. Logistic regression was u sed to explore the influence of this imbalance in risk factors. The mo del found seven independent risk factors (left ventricular failure, em ergency coronary bypass, redo bypass, nonuse of the internal thoracic artery, unstable angina, age, and diabetes) that significantly affecte d operative mortality. The FFS group variable closely approached indep endent risk significance at p = 0.059, This multivariable model explai ned only one third of the observed differences in actual mortality bet ween the HMO and PFS groups. The system-wide angioplasty/coronary bypa ss ratio, which could not be used in a patient-specific model, was 0.6 in the HMO system and 1.5 in the PFS group. Other factors related to the operating structure of a mature, large HMO may account for the rem ainder of the difference. The HMO referral system, through a powerful selection process, resulted in fewer emergencies, redo bypass operatio ns, and catheterization complications that, in turn, yielded lower ope rative mortality than a noncoordinated FFS system of cardiovascular ma nagement.