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Shop for Quality or Volume? Volume, Quality, and Outcomes of Coronary Artery Bypass Surgery

Andrew D. Auerbach, MD, MPH; Joan F. Hilton, ScD; Judith Maselli, MSPH; Penelope S. Pekow, PhD; Michael B. Rothberg, MD, MPH; and Peter K. Lindenauer, MD, MSc
[+] Article and Author Information

From the University of California, San Francisco, San Francisco, California, and Baystate Medical Center, Tufts University School of Medicine, Springfield, Massachusetts.


Acknowledgment: The authors acknowledge Erin Hartman, MS, for her expert editorial assistance, as well as Denise Remus, MD, and Kathy Belk for their work in assembling the data set used for this analysis.

Grant Support: By the California HealthCare Foundation (grant number 05-1755) and Agency for Healthcare Research and Quality (Patient Safety Research and Training Grant K08 HS11416-02; Dr. Auerbach).

Potential Financial Conflicts of Interest: None disclosed.

Requests for Single Reprints: Andrew D. Auerbach, MD, MPH, Department of Medicine, Division of Hospital Medicine, University of California, San Francisco, 505 Parnassus Avenue, Box 0131, San Francisco, CA 94143-0131; e-mail, ada@medicine.ucsf.edu.

Current Author Addresses: Dr. Auerbach and Ms. Maselli: Department of Medicine, Division of Hospital Medicine, University of California, San Francisco, 505 Parnassus Avenue, Box 0131, San Francisco, CA 94143-0131.

Dr. Hilton: Department of Epidemiology and Biostatistics, University of California, San Francisco, 505 Parnassus Avenue, San Francisco, CA 94143.

Drs. Pekow, Rothberg, and Lindenauer: Baystate Medical Center, Center for Quality and Safety Research, 759 Chestnut Street, Springfield, MA 01199.

Author Contributions: Conception and design: A.D. Auerbach, J.F. Hilton, J. Maselli, P.S. Pekow, P.K. Lindenauer.

Analysis and interpretation of the data: A.D. Auerbach, J.F. Hilton, J. Maselli, P.S. Pekow, M.B. Rothberg, P.K. Lindenauer.

Drafting of the article: A.D. Auerbach, J.F. Hilton, P.S. Pekow, M.B. Rothberg.

Critical revision of the article for important intellectual content: A.D. Auerbach, J.F. Hilton, P.S. Pekow, M.B. Rothberg, P.K. Lindenauer.

Final approval of the article: A.D. Auerbach, J.F. Hilton, P.S. Pekow, M.B. Rothberg, P.K. Lindenauer.

Provision of study materials or patients: A.D. Auerbach, J.F. Hilton, P.S. Pekow, P.K. Lindenauer.

Statistical expertise: A.D. Auerbach, J.F. Hilton, P.S. Pekow.

Obtaining of funding: A.D. Auerbach, J.F. Hilton, P.S. Pekow.

Administrative, technical, or logistic support: A.D. Auerbach, J.F. Hilton, P.S. Pekow.

Collection and assembly of data: A.D. Auerbach, J.F. Hilton, P.S. Pekow.


Ann Intern Med. 2009;150(10):696-704. doi:10.7326/0003-4819-150-10-200905190-00007
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Table 2 shows patient characteristics: 81 289 patients had coronary artery bypass grafting at 1 of the study sites from 1 October 2003 to 1 September 2005. The mean age of patients was 65.0 years (SD, 10.9), and 72% were men. Most were white, were married, and had Medicare insurance. The most common comorbid conditions in our cohort were hypertension (72%), diabetes without chronic complications (31%), and chronic obstructive pulmonary disease (23%). Most patients received care at nonteaching hospitals in the southern United States. Two percent (1825 of 81 289) of patients died, and 11% were readmitted in 30 days.

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Figure.
Adjusted mortality rates of patients undergoing coronary artery bypass surgery, by quartile of hospital volume and count of missed quality measures and by quartile of surgeon volume and count of missed quality measures.

Models are adjusted for age, sex, diagnosis-related group–predicted mortality, congestive heart failure, hypertension, neurologic disorders, diabetes with complications, renal failure, coagulopathy, deficiency anemia, whether an internal mammary graft was used during the procedure, the volume and number of missed quality measures, and the interaction between volume and number of missed quality measures. Top. A strong association between the number of quality measures missed and death across all quartiles of hospital volume is observed, with mortality rates similar across quartiles of hospital volume if no quality measures are missed. Bottom. A strong association between the number of quality measures missed and mortality rates across all quartiles of surgeon volume is observed, with similar mortality rates even for lowest-volume surgeons if no quality measures are missed.

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Shopping for Data: Quality or Volume?
Posted on May 25, 2009
Kevin W. Lobdell
Carolinas Heart and Vascular Institute
Conflict of Interest: None Declared

The manuscript focuses our attention on important process and outcome measures in surgical coronary artery revascularization, but fails to address some very practical limitations of the voluminous administrative data. Specifically, quality measures related to statins, aspirin, and beta -blockers within two days of surgery is of limited value if not taken in context. Not uncommonly, a clinical situation may exclude a patient from one of the treatments, yet the exclusion criteria do not address these issues. Examples include: 1) typically, patients that remain mechanically ventilated would not be given a lipid-lowering agent, 2) patients with significant post-operative thrombocytopenia or coagulopathy may not be given aspirin until the platelet count increases or coagulopathy improves, 3) beta-blockers would not be administered when inotropes (mediated through beta-receptor agonists such as dopamine, dobutamine, epinephrine, and norepinephrine) are continued. Similarly, patients prophylaxed or treated with amiodarone for atrial fibrillation would not commonly be given beta-blockers.

A generally accepted risk model, such as the Society of Thoracic Surgeons-National Cardiac Database, would also have added significantly to value of the comparisons. Bias cannot be excluded, since some institutions or surgeons may operate on a higher percentage of "risky" patients than others.

Unfortunately, without the aforementioned contextual information, it is difficult to determine the value of this investigation. Let us suggest that as we shop for data, quality is more valuable than volume.

Conflict of Interest:

None declared

The Authors Respond
Posted on July 15, 2009
Andrew D Auerbach
UCSF Department of Medicine
Conflict of Interest: None Declared

The Authors reply:

Dr. Lobdell points out challenges inherent to interpreting results from analyses using highly detailed claims data. While our approach did not exclude patients on amiodarone or pressors specifically (1), it did exclude patients with a wide range of contraindications (hypotension, heart failure, and bleeding). Nevertheless, we may have misclassified a small number of patients with acceptable contraindications, perhaps partially explaining the inconsistent relationship between individual measures and mortality seen. However, it is less obvious how misclassification would produce a strong association between overall quality and improved outcomes.

While our risk adjustment models did not contain the clinical data used in the Society of Thoracic Surgeons approach, we saw no statistical association between surgeon or hospital volume and severity of illness as measured by APR-DRG risk of mortality score. As a result, we feel it would require a very large number of patients with important and unmeasured comorbidities to influence our results unduly. Interestingly, the difference between clinical data-driven models (such as STS's) and administrative data-driven models power is relatively small when comparisons are made at the aggregate level (2) "“ such as in our study.

While Dr. Lobdell raises points potentially useful in interpreting our study findings, we would strongly disagree that our results are driven entirely by poor quality data or inadequate risk adjustment. It is highly unlikely that the strong associations we saw between highest quality care and improved outcomes in our study are due to poor quality data. Rather, we hope our study prompts further examination of the benefits of improving the reliability of perioperative care, and compels the development of systems that maximize care quality from start to finish.

References:

1. Auerbach AD, Hilton JF, Maselli J, Pekow PS, Rothberg MB, Lindenauer PK. Shop for quality or volume? Volume, quality, and outcomes of coronary artery bypass surgery. Ann Intern Med. 2009;150(10):696-704.

2. Pine M, Jordan HS, Elixhauser A, et al. Enhancement of claims data to improve risk adjustment of hospital mortality. JAMA. 2007;297(1):71-6.

Conflict of Interest:

None declared

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