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Hospital coronary artery bypass graft surgery volume and patient mortality, 1998-2000
Saif S Rathore1, Andrew J Epstein, Kevin G M Volpp
1Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA.
Insights
Higher annual hospital volume for coronary artery bypass graft (CABG) surgery is associated with lower in-hospital mortality. However, hospital CABG volume alone is not a reliable indicator of quality care.
Area of Science:
- Cardiovascular Surgery
- Health Services Research
- Quality Improvement
Background:
- The Leapfrog Group recommends a minimum annual volume of 500 coronary artery bypass graft (CABG) procedures per hospital to reduce mortality.
- Current evidence on the applicability of this volume standard to contemporary practice is limited.
Purpose of the Study:
- To investigate the relationship between annual hospital coronary artery bypass graft (CABG) surgery volume and in-hospital mortality rates.
- To assess whether current volume standards accurately reflect hospital quality for CABG procedures.
Main Methods:
- Retrospective analysis of the National Inpatient Sample database (1998-2000) including 228,738 patients undergoing CABG.
- Hospitals were categorized into low (12-249), medium (250-499), and high (>=500) annual CABG volume groups.
- Multivariable logistic regression was used to adjust for patient and hospital factors influencing mortality risk.
Main Results:
- Crude in-hospital mortality rates decreased with increasing CABG volume: 4.21% (low), 3.74% (medium), and 3.54% (high) (P < 0.001).
- After adjustment, patients at low-volume hospitals had significantly higher mortality risk (OR 1.26) compared to high-volume hospitals.
- Risk-standardized mortality rates showed considerable variation within all volume groups, with most hospitals performing at or below expected rates.
Conclusions:
- While higher annual hospital coronary artery bypass graft (CABG) volume is associated with lower average in-hospital mortality, the difference is modest.
- The significant heterogeneity in outcomes within each volume category suggests that individual hospital CABG volume is not a definitive marker of quality.
- Further research is needed to identify more reliable indicators of CABG quality beyond procedural volume.
Objective:
To evaluate the association between annual hospital coronary artery bypass graft (CABG) surgery volume and in-hospital mortality.
Summary Background Data:
The Leapfrog Group recommends health care purchasers contract for CABG services only with hospitals that perform >or=500 CABGs annually to reduce mortality; it is unclear whether this standard applies to current practice.
Methods:
We conducted a retrospective analysis of the National Inpatient Sample database for patients who underwent CABG in 1998-2000 (n = 228738) at low (12-249 cases/year), medium (250-499 cases/year), and high (>or=500 cases/year) CABG volume hospitals. Crude in-hospital mortality rates were 4.21% in low-volume hospitals, 3.74% in medium-volume hospitals, and 3.54% in high-volume hospitals (trend P < 0.001). Compared with patients at high-volume hospitals (odds ratio 1.00, referent), patients at low-volume hospitals remained at increased risk of mortality after multivariable adjustment (odds ratio 1.26, 95% confidence interval = 1.15-1.39). The mortality risk for patients at medium-volume hospitals was of borderline significance (odds ratio 1.11, 95% confidence interval = 1.01-1.21). However, 207 of 243 (85%) of low-volume and 151 of 169 (89%) of medium-volume hospital-years had risk-standardized mortality rates that were statistically lower or comparable to those expected. In contrast, only 11 of 169 (6%) of high-volume hospital-years had outcomes that were statistically better than expected.
Conclusions:
Patients at high-volume CABG hospitals were, on average, at a lower mortality risk than patients at lower-volume hospitals. However, the small size of the volume-associated mortality difference and the heterogeneity in outcomes within all CABG volume groups suggest individual hospital CABG volume is not a reliable marker of hospital CABG quality.
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