Interpreting the Volume-Outcome Relationship in the Context of Health Care Quality Workshop Summary (2000) / Chapter Skim
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Appendix C: How is Volume Related to Quality in Health Care? A Systematic Review of the Research Literature?
Appendix C: How is Volume Related to Quality in Health Care? A Systematic Review of the Research Literature?
Pages 27-102
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From page 27... ...
. surgery, carotid endarterectomy, abdominal aortlc aneurysm repair, cancer surgery, percutaneous transluminal coronary angioplasty (PTCA)
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Few investigations have assessed differences in specific clinical processes of care, especially those known to affect outcomes. One intriguing exception showed that about one third of the mortality difference between high- and Tow-volume hospitals for acute myocardial infarction could be attributed to more frequent use of proven-effective medications at high-volume hospitals.
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, a large body of research has focused on measuring and explaining the relationship between patient outcomes and the volume of specific health services provided by hospitals and physicians. Many studies have documented that higher volume is associated with better outcomes for a variety of different surgical procedures and medical conditions.
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Some have little time or choice (e.g., those suffering acute myocardial infarction or ruptured aortic aneurysms)
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Does superior performance in carotid endarterectomy or aortic aneurysm surged derive from experience with just those procedures, or is the volume of other major vascular surgical procedures important also? This issue may be termed the "volume of what" question.
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Third, is the experience of other key participants important? is the volume of experience in a hospital's emergency department or coronary care unit important to its outcomes for patients with acute myocardial infarction?
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A professional reference librarian assisted us in the development of our search strategy. First, we selected twelve conditions and procedures for which volume and outcomes had been studied (coronary artery bypass, carotid endarterectomy, peripheral vascular surgery, trauma, transplant, hip surgery, knee surgery, liver resection lung resection cancer .sur~erv an~ionla.stv and myocardial infarction)
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This monograph includes the findings of our review of eight procedures and conditions: coronary artery bypass graft (CABG) surgery, pediatric cardiac surgery, carotid endarterectomy, abdominal aortic aneurysm repair, cancer surgery, coronary angioplasty, acute myocardial infarction, and AIDS.
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This was particularly common among the studies of coronary angioplasty and cancer. These were primarily early studies of multiple surgical procedures that analyzed data from the 1970s.
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of Studies No. of Studies Condition Reviewed Included Excluded Coronary Artery Bypass Graft 19 9 10 Pediatric Cardiac Surgery 3 3 0 Carotid Endarterectomy 24 18 6 Abdominal Aortic Aneurysm 16 12 4 Cancer Surgery 45 28 17 Coronary Angioplasty 20 9 11 Acute Myocardial Infarction 13 3 10 AIDS 9 6 3 Mulitple Procedures 13*
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that examined more than just mortality were primarily studies of carotid endarterectomy that considered death or stroke as primary outcomes and investigations of coronary angioplasty that focused on death or emergency coronary artery bypass grafting together as major adverse events. The vast majority of investigators examined provider volume as a categorical variable.
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Volume and Outcome in Coronary Artery Bypass Graft (CABG) Surgery: Nineteen articles treating various aspects of the subject of volume and outcome in CAB G surgery were identified by our venous search strategies.
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selection or clinical processes of care. All 9 studies employed riskadjustment methods in analyzing outcomes; 7 used administrative data and 2 used clinical data.
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In contrast, Sollano et al examined the experience in New York State between 1990 and 1995 and found no relationship between inpatient death and hospital volume.
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took a different analytic approach to constructing complexity categories and had access to prospectively collected clinical data to evaluate volume and inpatient mortality in New York State from 1992 to 1995. (Hannan 1998a)
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Only 9 of the 19 studies performed any type of risk adjustment. Among studies that did attempt to adjust for patient risk factors, five relied on administrative data, and four had clinical data.
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focused on 30 day death rates, some with combined death, stroke, and myocardial infarction rates. Because of the well-documented difficulties of using administrative data to differentiate pre-operative versus post-operative strokes, we only considered the 4 studies that had medical chart review data to have valid measures of perioperative stroke or myocardial infarction.
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Operating at high volume hospitals had the lowest death rates (0.94%~. It is also worth noting that in New York State, there were very few operations performed by low volume surgeons in high volume hospitals, so estimates of mortality rates in this subgroup had very wide 95% confidence intervals.
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not just aortic aneurysm repairs. All but the Amundsen study performed some type of risk adjustment, and the Khuri study of Veterans Affairs hospitals was the only one to use clinical data for risk adjustment.
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They found that for unruptured AAAs, hospital volume was related to outcome, but that surgeon volume was not. By contrast, for ruptured AAAs, surgeon volume, but not hospital volume, was related to outcome.
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analyzed both physician and hospital volumes; 1,972 procedures were performed by 748 surgeons in ~ 84 hospitals in New York State from ~ 984 to 1991. In separate analyses of surgeon volume and hospital volume, high-volume surgeons (>41 cases per year)
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The number needed to treat by a high volume provider to prevent one inpatient death attributable to low volume was seven to nine patients. Breast Cancer Surgery The two studies of breast cancer surgery had relatively high quality scores (10 and ~ I)
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The authors conjectured that since breast surgery has negligible operative and inpatient mortality, the volumeoutcome relationship might be caused by higher-volume hospitals providing more effective adjuvant treatment. Sainsbury et al studied 12,861 cases of breast cancer surgery performed by 180 surgeons in the Yorkshire Regional Health Authority area from 1979 to 1988.
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used clinical data. Two studies examined clinical processes, but neither incorporated the processes into their risk adjustment model.
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Seven of the nine were derived from large statewide or national hospital discharge databases. Overall quality scores ranged from 7 to 14, with a median score of ~ (IQR, 8-9~.
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The study by Hannan and colleagues (1997a) using the New York State Coronary Angioplasty Reporting System reported the most robust risk adjustment model with a C statistic of O.89.
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They relied on administrative data for risk adjustment. The authors reported that higher physician volume was associated with lower risk adjusted rates of the combined endpoint of in-hospital death or CAB G
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Volume and Outcome in Acute Myocardial Infarction While there is an enormous health services research literature on acute myocardial infarction, we were only able to identify three studies that met our inclusion (See Appendix I.) Eight other studies were identified by our search algorithm but excluded because they did not explicitly evaluate volume and outcome relationships.
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In analyses that used administrative data (including the Disease Staging severity system using ICD-9 discharge diagnosis) for risk adjustment, they reported that a 10% increase in caseload corresponded to a 2.2% absolute decrease in inpatient mortality rates.
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All used at least administrative data to risk-adjust rates of death, and 2 used clinical data but none presented data documenting good discrimination or calibration. All six demonstrated statistically significant inverse associations between hospital or physician volume and death rates.
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There can be little doubt that for a wide variety of medical conditions and surgical procedures, patients treated at higher volume hospitals or by higher volume physicians experience on average lower mortality rates than those treated by
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In absolute terms, significant differences between high and low volume hospitals ranged from about ~ death (or fewer) per 100 patients treated in PICA and carotid endarterectomy to 5-10 per 100 in some studies of CABG, pediatric cardiac surgery, and AAA surgery.
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This effect is even more pronounced when the event representing the numerator of the proportion is uncommon. Figure 4 illustrates this phenomenon by plotting the hospital mortality rates for all 5705 hospitals treating one or more Medicare beneficiaries with an acute myocardial infarction in 1984 (Chassin 1989~.
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Current research did not address the extent to which (if any) the differences between high and low volume providers may be associated with differences in appropriateness of patient selection.
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might use data on volume and outcomes to improve performance. A program of public availability of data on hospital or physician volume of services would have the advantage of access to reliable and reasonably timely data (at least on hospital volume)
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As a new generation of research produces more such data, the prospect of substantial improvement will increase. Among the most important research efforts to encourage are those which build prospectively-compiled, clinical databases that include all patients and all providers.
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From page 63... ...
Volume 2 categories Multiple 0 1 8. Risk adjustment: none admin clinical clinical+ 0 1 2 3 only data C>.75 and H/L test + 9.
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From page 64... ...
OR myocardial infarction/mesh] OR vascular surgical procedurestmesh]
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From page 77... ...
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From page 81... ...
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- ~ i, '6~l~i ~ ~ tA by.
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From page 89... ...
The relation between quantity and quality with coronary artery bypass graft (CAB G) surgery.
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From page 90... ...
Outcome as a function of annual coronary artery bypass graft volume. The Ad Hoc Committee on Cardiac Surgery Credentialing of The Society of Thoracic Surgeons.
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From page 91... ...
Quality of care for Medicare patients with acute myocardial infarction. A four-state pilot study from the Cooperative Cardiovascular Project.
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From page 92... ...
. Predictors of success and major complications for primary percutaneous transTuminal coronary angioplasty in acute myocardial infarction.
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Ir., Chassin MR. The decline in coronary artery bypass graft surgery mortality in New York State.
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Hospital and patient characteristics associated with variation in 28-day mortality rates for very Tow birth weight infants. Vermont Oxford Network.
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Operative mortality rates for intact and ruptured abdominal aortic aneurysms in Michigan: an eleven-year statewide experience.
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From page 96... ...
Volume and mortality in coronary artery bypass grafting "published erratum appears in BM]
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From page 97... ...
Elderly patients at highest risk with acute myocardial infarction are more frequently transferred Tom community hospitals to tertiary centers: reality or myth? Am Heart ]
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From page 98... ...
Pett SB, Jr. Coronary artery bypass grafting volume and mortality.
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Innovation, centralization, and growth. Coronary artery bypass graft surgery in Manitoba.
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Warner BA, et al. No continuous relationship between Veterans Affairs hospital coronary artery bypass grafting surgical volume and operative mortaTity.
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From page 101... ...
Coronary artery bypass mortality rates in Ontario. A Canadian approach to quality assurance in cardiac surgery.
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From page 102... ...
, Bilf~nger TV, Anagnostopoulos CE. Coronary artery bypass grafting.
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