Abstract & Commentary
Synopsis: Mortality decreased as volume increased for all 14 procedures examined in this large study. Mortality differences between very-low and very-high volume hospitals were highest for pancreatic resection (16.3% vs 3.8%) and lowest for carotid endarterectomy (1.7% vs 1.5%).
Source: Birkmeyer JD, et al. N Engl J Med. 2002;346: 1128-1137.
Hospital volume (the number of procedures performed at a hospital) is known to affect surgical mortality. This study was undertaken to clarify the relationship between hospital volume and surgical mortality for 6 different types of cardiovascular procedures and 8 types of major cancer resections. The procedures were selected because all are relatively complex, associated with a nontrivial risk of operative mortality, and most often are performed on an elective basis. The sample included 2.5 million Medicare patients who underwent surgery between 1994 and 1999, who were identified using the national Medicare claims database and the Nationwide Inpatient Sample. Patients who were younger than 65 years or older than 99 years were excluded, as were the approximately 10% of Medicare patients enrolled in risk-bearing HMOs. Mortality was defined as the rate of death before hospital discharge or within 30 days after the index procedures. Hospital volume was defined as the total number of procedures performed at the institution, not the number of procedures performed on Medicare patients. Five categories of volume were identified (very low, low, medium, high, very high).
Mortality decreased as volume increased for all 14 types of procedures (P < 0.001). The relative importance of volume varied markedly according to the type of procedure. Absolute differences in adjusted mortality rates between very-low-volume hospitals and very-high-volume hospitals ranged from more than 12% (for pancreatic resection, 16.3% vs 3.8%) to only 0.2% (for carotid endarterectomy, 1.7% vs 1.5%). The absolute difference in adjusted mortality rates between very-low-volume hospitals and very-high-volume hospitals was greater than 5% for esophagectomy and pneumonectomy, 2-5% for gastrectomy, cystectomy, repair of a nonruptured abdominal aneurysm, and replacement of an aortic or mitral valve, and less than 2% for coronary artery bypass grafting (CABG), lower extremity bypass, colectomy, lobectomy, and nephrectomy. Birkmeyer and associates concluded that, in the absence of other information about the quality of surgery at the hospitals near them, Medicare patients undergoing selected cardiovascular or cancer procedures can significantly reduce their risk for operative death by selecting a high-volume hospital.
Comment by Leslie A. Hoffman, RN, PhD
Findings of this study, likely the largest conducted to date, support a relationship that has been documented in several prior studies, namely that higher hospital volume translates into lower surgical mortality rates. The primary goal of this study was to examine hospital volume in regard to selected procedures, and marked variations were found in the absolute magnitude of difference between very-low-volume and very-high-volume hospitals. For all procedures, an inverse relationship was seen. Surgical mortality was significantly lower in very-high-volume hospitals compared to very-low-volume hospitals. However, there were marked differences among the types of procedures with the highest differences seen for procedures that are less frequently performed, eg, pancreatic resection (12.5%) and esophagectomy (11.9%).
Even small differences can be important. Considering procedure frequency, the researchers concluded that 314 deaths a year could have been avoided if the morality rate for CABG procedures (very common; volume had a moderate effect) at very-low-volume hospitals was reduced to that at very-high-volume hospitals. Conversely, 32 deaths a year would have been avoided for pancreatic resection (relatively uncommon; volume had a large effect).
It is notable that a recent review of 128 analyses involving 40 different procedures reported lower mortality at higher volume hospitals in 123 (96%) cases.1 Therefore, it seems reasonable to promote use of high-volume centers where differences are the greatest and/or to establish some minimum standards for procedure frequency. The Leapfrog Group, a consortium that provides health insurance to more than 33 million people, has set volume thresholds for 5 procedures: CABG (500 per year), coronary angioplasty (400 per year), carotid endarterectomy (100 per year), elective abdominal aortic aneurysm repair (30 per year) and esophagectomy for cancer (6 per year).2 Group members are promoting selective referral in urban centers through education and, in some cases, financial incentives.
Many object to such initiatives, noting that some low-volume hospitals have superior outcomes. However, it is difficult for the public to obtain such information. Notably, health care providers tend to follow similar guidelines. Few health care providers would knowingly suggest that a family member or friend undergo a high-risk, elective procedure at a hospital where such operations were rarely performed or refer to a physician who rarely performed the procedure. Absent reporting systems that provide appropriate information, it appears that the best way to improve one’s odds of survival is to select a high-volume hospital.
Dr. Hoffman is Professor Medical-Surgical Nursing Chair, Department of Acute/Tertiary Care, Massachusetts General Hospital, Cambridge, MA.
References
1. Dudley RA, et al. Selective referral to high-volume hospitals: Estimating potentially avoidable deaths. JAMA. 2000;283:1159-1166.
2. Birkmeyer JD, et al. Volume standards for high-risk surgical procedures: Potential benefits of the Leapfrog initiative. Surgery. 2001;130:415-422.
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