ORIGINAL ARTICLE

Hospital Volume and Operative Mortality in the Modern Era Bradley N. Reames, MD, MS, Amir A. Ghaferi, MD, MS, John D. Birkmeyer, MD, and Justin B. Dimick, MD, MPH

Objective: To determine whether the relationship between hospital volume and mortality has changed over time. Background: It is generally accepted that hospital volume is associated with mortality in high-risk procedures. However, as surgical safety has improved over the last decade, recent evidence has suggested that the inverse relationship has diminished or been eliminated. Methods: Using national Medicare claims data from 2000 through 2009, we examined mortality among 3,282,127 patients who underwent 1 of 8 gastrointestinal, cardiac, or vascular procedures. Hospitals were stratified into quintiles of operative volume. Using multivariable logistic regression models to adjust for patient characteristics, we examined the relationship between hospital volume and mortality, and assessed for changes over time. We performed sensitivity analyses using hierarchical logistic regression modeling with hospital-level random effects to confirm our results. Results: Throughout the 10-year period, a significant inverse relationship was observed in all procedures. In 5 of the 8 procedures studied, the strength of the volume-outcome relationship increased over time. In esophagectomy, for example, the adjusted odds ratio of mortality in very low volume hospitals compared to very high volume hospitals increased from 2.25 [95% confidence interval (CI): 1.57–3.23] in 2000–2001 to 3.68 (95% CI: 2.66–5.11) in 2008– 2009. Only pancreatectomy showed a notable decrease in strength of the relationship over time, from 5.83 (95% CI: 3.64–9.36) in 2000–2001, to 3.08 (95% CI: 2.07–4.57) in 2008–2009. Conclusions: For all procedures examined, higher volume hospitals had significantly lower mortality rates than lower volume hospitals. Despite recent improvements in surgical safety, the strong inverse relationship between hospital volume and mortality persists in the modern era. Keywords: cardiac surgery, gastrointestinal surgery, health policy, health services research, hospital volume, operative mortality, quality improvement, surgical outcomes, vascular surgery (Ann Surg 2014;260:244–251)

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vidence that hospital volume influences outcomes has been verified in nearly every major type of surgery.1–3 This body of work highlighted important and previously unrecognized variations in hospital performance and ignited efforts to improve surgical quality among poorly performing hospitals. In an effort to reduce these variations among hospitals, new health policy and quality improvement initiatives, such as public reporting, pay-for-performance, and surgi-

From the Center for Healthcare Outcomes and Policy, University of Michigan, Ann Arbor, MI. Disclosure: B.N.R. is supported by a grant from the National Cancer Institute (5T32CA009672-23). J.B.D. is supported by grant from the National Institute on Aging (5R01AG039434-03). These funding sources had no involvement in the manuscript herein. B.N.R. and A.A.G. have no conflicts of interest or disclosures related to the content of this manuscript. Both J.D.B. and J.B.D. have an equity interest in ArborMetrix, Inc, which provides software and analytics for measuring hospital quality and efficiency. The company had no role in this study. Reprints: Bradley N. Reames, MD, MS, Center for Healthcare Outcomes and Policy, University of Michigan, Building 16, Room 100N-08, 2800 Plymouth Road, Ann Arbor, MI 48109. E-mail: [email protected]. C 2013 by Lippincott Williams & Wilkins Copyright  ISSN: 0003-4932/13/26002-0244 DOI: 10.1097/SLA.0000000000000375

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cal checklists, have been implemented to promote best practice and improve standards of care.4–7 Over the last decade, surgical mortality rates have significantly decreased throughout the country, possibly due to these measures.8–10 As a result, it is unclear whether the volume-outcome relationship has persisted in the modern era. Recent improvements in surgical outcomes could change the relationship between volume and outcome in 2 possible ways. First, advances in surgical care could weaken or eliminate the influence of hospital volume on patient outcomes. Alternatively, despite absolute decreases in mortality, relative differences may persist between hospitals and the relationship endures over time. Recently published evidence supports the former hypothesis, asserting that the volume-outcome relationship is severely attenuated in recent years.11 However, this single study represents only a subset of US hospitals in 1 year and may not be generalizable to all hospitals or longer periods. Given the incorporation of volume standards into several health policy initiatives (eg, Centers of Excellence,12 Leapfrog Initiative13,14 ), as well as accreditation processes and local credentialing decisions, it is important for policymakers and surgical leaders to understand whether the volume-outcome relationship has changed over time. Given this uncertainty, we sought to evaluate whether the relationship between hospital volume and operative mortality has changed during a recent 10-year period, using a national data set of high-risk patients. To do this, we examined the risk-adjusted operative mortality of Medicare patients undergoing 1 of 8 complex gastrointestinal, cardiac, or vascular procedures at hospitals in the lowest and highest quintiles of operative volume during the years 2000 to 2009.

METHODS Data Source and Study Population To complete this study, we utilized analytic files for the years 2000 to 2009 from the Center for Medicare and Medicaid Services. The Medicare Provider Analysis and Review file, which contains hospital discharge records for fee-for-service acute care hospitalizations of all Medicare beneficiaries not enrolled in managed care plans, was used to create the main data sets for analysis, and the Medicare Denominator file was used to determine vital status of patients 30 days after surgery. The institutional review board of the University of Michigan and the Center for Medicare and Medicaid Services approved this protocol and waived the requirement for informed consent. We identified patients between the ages of 65 and 99 years who underwent 1 of 3 gastrointestinal (colectomy, esophagectomy, and pancreatectomy), 3 cardiac (aortic valve replacement, mitral valve replacement, and coronary artery bypass grafting), or 2 vascular procedures (abdominal aortic aneurysm repair and carotid endarterectomy) during the study period, using appropriate procedure codes from the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). Patients undergoing open, laparoscopic, minimally invasive, and endovascular approaches were included in this analysis. These procedures were selected prospectively as they represent commonly performed complex elective procedures with nontrivial risks of mortality, for which previous literature has reported an association between volume and operative mortality of varying strengths.1,2,15 Annals of Surgery r Volume 260, Number 2, August 2014

Copyright © 2013 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

Annals of Surgery r Volume 260, Number 2, August 2014

Hospital Volume and Operative Mortality

TABLE 1. Patient Characteristics Among Very Low and Very High Volume Quintiles for the 8 Procedures During the Study Period Time Period 2000–2001

2002–2003

2004–2005

2006–2007

2008–2009

Hospital Volume Procedure

Very Low

Pancreatectomy Medicare patients (N) Age >75 yrs (%) Female (%) African American race (%) Nonelective admission (%) ≥3 Comorbid conditions (%) Colectomy Medicare patients (N) Age >75 yrs (%) Female (%) African American race (%) Nonelective admission (%) ≥3 Comorbid conditions (%) Esophagectomy Medicare patients (N) Age >75 yrs (%) Female (%) African American race (%) Nonelective admission (%) ≥3 Comorbid conditions (%) Coronary artery bypass grafting Medicare patients (N) Age >75 years (%) Female (%) African American race (%) Nonelective admission (%) ≥3 Comorbid conditions (%) Aortic valve replacement Medicare patients (N) Age >75 years (%) Female (%) African American race (%) Nonelective admission (%) ≥3 Comorbid conditions (%) Mitral valve replacement Medicare patients (N) Age >75 yrs (%) Female (%) African American race (%) Nonelective admission (%) ≥3 Comorbid conditions (%) Abdominal aortic aneurysm repair Medicare patients (N) Age >75 yrs (%) Female (%) African American race (%) Nonelective admission (%) ≥3 Comorbid conditions (%) Carotid endarterectomy Medicare patients (N) Age >75 yrs (%) Female (%) African American race (%) Nonelective admission (%) ≥3 Comorbid conditions (%)

 C 2013 Lippincott Williams & Wilkins

Very High

Very Low

38.5 47.2 3.8 10.7 21.8

38.8 53.5 10.6 41.8 39.2

5002 37.3 51.0 8.3 37.9 33.8

263,232 38.1 38.5 34.2 34.0 4.6 5.3 54.8 54.3 21.6 21.1

42.6 32.2 9.4 34.0 37.2

52.1 42.5 4.8 36.0 22.0

45.1 58.0 3.1 43.5 12.6

43.5 60.2 5.6 42.4 17.2

45.2 25.8 3.2 19.2 27.8

43.3 29.9 6.3 24.3 32.5

17,462

42.3 50.9 9.0 32.4 41.2

43.5 31.9 9.2 33.9 40.3

52.9 42.7 4.5 35.7 26.0

47.2 57.8 4.0 42.4 14.3

45.8 57.7 6.1 42.7 20.5

47.4 24.2 3.4 16.6 29.7

46.4 28.7 6.1 22.6 35.0

42.3 50.2 4.4 10.1 33.1

39.0 53.0 9.0 32.3 36.3

43.2 34.6 8.0 31.2 39.8

221,423 53.3 51.2 58.9 58.8 8.9 8.6 51.2 39.4 33.9 31.3 39.7 29.6 8.2 29.2 31.7

51.0 58.2 4.4 41.7 15.8

46.7 57.9 6.1 42.8 41.5

49.9 23.9 3.8 15.5 29.2

50.1 26.8 5.3 21.6 41.6

76,649 60.8 42.5 2.8 35.9 40.3

53.5 41.4 4.9 33.8 46.0

52.3 58.5 4.5 41.8 38.0

43.8 58.3 7.4 40.1 43.8

52.4 23.7 3.6 16.3 37.7

49.5 26.1 5.8 21.4 40.2

11,539

46,105

59.7 40.9 2.9 35.1 43.9 14,146

47,289

112,339 52.2 49.3 46.2 44.0 5.2 3.2 26.9 16.8 27.2 26.2

33.8 24.1 3.8 6.8 24.1

178,849 36.4 27.8 31.7 30.8 6.4 6.0 50.5 51.7 41.4 38.5

54,175 56.2 42.0 4.6 35.5 41.0

40.3 48.2 5.5 11.6 31.8

6601 33.7 25.5 2.8 6.5 28.4

155,625 40.2 41.0 32.0 32.0 6.4 6.4 51.3 52.5 39.4 39.7

58.2 42.1 3.2 36.6 22.7

Very High 8571

5204 32.8 26.1 3.1 6.3 23.7

13,593

144,130 51.1 48.8 45.7 43.5 4.6 2.8 26.0 18.6 23.5 22.5

Very Low

162,525 56.8 55.6 59.0 59.0 9.1 8.1 51.9 40.6 38.3 36.2

52,594 56.5 41.6 2.8 37.9 19.7

Very High 5944

189,273 39.6 40.3 32.9 32.6 6.6 5.9 51.8 54.9 29.1 28.6

51,962

148,468 50.9 47.3 46.1 43.5 4.3 2.8 29.1 23.6 20.7 19.4

42.8 51.1 4.1 9.8 31.2

5464 32.0 23.8 3.2 8.2 20.8

16,736

51,043

Very Low

170,009 56.8 54.7 59.8 59.7 9.0 8.9 52.4 41.9 36.9 34.2

56,636 56.0 43.2 2.1 35.4 17.2

Very High 5564

242,362 37.8 38.2 33.6 33.3 6.3 5.6 52.6 53.5 25.0 25.4

52,847

43.2 31.3 6.1 27.8 29.6

39.8 52.8 10.3 37.2 41.0

6046 30.6 25.7 4.1 11.4 19.8

41.4 58.6 5.6 42.9 14.4

37.2 52.2 3.7 11.1 24.2

191,656 56.0 53.6 59.4 59.0 9.1 8.5 53.4 42.9 34.2 32.5

6315

52.5 42.5 4.9 37.8 18.7

Very Low

5651

186,300 56.6 54.6 59.9 59.2 9.1 7.3 55.2 44.6 31.5 30.1 43.4 31.2 8.4 34.4 34.2

Very High

48.6 56.7 5.7 41.1 43.7 62,327

103,038 53.2 51.0 45.8 42.8 4.8 3.0 23.6 16.0 32.4 32.5

49.6 24.5 3.7 14.7 40.2

127,433 51.2 49.6 44.6 42.7 5.5 3.3 23.6 14.2 34.4 33.6

www.annalsofsurgery.com | 245

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Annals of Surgery r Volume 260, Number 2, August 2014

Reames et al

TABLE 2. Distribution of Hospitals and Hospital Volume Among Very Low and Very High Volume Quintiles for the 8 Procedures During the Study Period Time Period 2000–2001

2002–2003

2004–2005

2006–2007

2008–2009

Hospital Volume Very Low

Procedure

Very High

Pancreatectomy Hospitals (N) 1237 Hospitals per quintile (N) 866 15 Annual procedure volume 17 Colectomy Hospitals (N) 4259 Hospitals per quintile (N) 2621 177 Annual procedure volume 82 Esophagectomy Hospitals (N) 1559 Hospitals per quintile (N) 1023 27 Annual procedure volume 12 Coronary artery bypass grafting Hospitals (N) 1069 Hospitals per quintile (N) 569 53 Annual procedure volume 480 Aortic valve replacement Hospitals (N) 1024 Hospitals per quintile (N) 587 39 Annual procedure volume 107 Mitral valve replacement Hospitals (N) 975 Hospitals per quintile (N) 562 34 Annual procedure volume 42 Abdominal aortic aneurysm repair Hospitals (N) 2301 Hospitals per quintile (N) 1511 64 Annual procedure volume 73 Carotid endarterectomy Hospitals (N) 2569 Hospitals per quintile (N) 1602 96 Annual procedure volume 141

Very Low

Very High

Very Low

14 >22

674 88

2638 12

880 422

594 112

636 38

607 78

1367 134

1502 18 1189

1150

69 >272 1159

1069

39 >135 1077

1913

2444

Very High 926

1216

2050

2487 1532 17

Very Low

3920

1049

2167 1451

Hospital volume and operative mortality in the modern era.

To determine whether the relationship between hospital volume and mortality has changed over time...
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