Hospitals with high volumes of patients who have myocardial infarction, heart failure, and pneumonia have lower 30-day mortality rates for each of those conditions, compared with hospitals that treat fewer such patients.
The relationship between hospital volume and mortality diminished among high-volume hospitals, and was no longer significant once the number of patients exceeded a threshold for each condition, according to a cross-sectional analysis of Medicare claims from more than 4,000 hospitals.
The study is the first to examine the relationship between hospital volume and death from heart failure.
It is one of the few studies that examines the link between volume and mortality in myocardial infarction and pneumonia, wrote Dr. Joseph S. Ross of the Mount Sinai School of Medicine, New York, and his associates (N. Engl. J. Med. 2010;362:1110–8).
The researchers analyzed data on fee-for-service Medicare patients aged 65 or older who were hospitalized between Jan. 1, 2004, and Dec. 31, 2006, with myocardial infarction, heart failure, or pneumonia. The mean age for all patients was 80 years. To avoid survival bias, for each patient who had multiple admissions for one of the three conditions in a given year, one admission per year was selected at random for inclusion in the analysis. Transfers between facilities were tallied with the index hospital.
To categorize hospital volume as low, medium, or high, the investigators stratified into quartiles the mean annual number of patients hospitalized for each condition during the 3-year study period.
Hospitals in the first and second quartiles were categorized as low volume, those in the third quartile as medium, and those in the fourth quartile as high.
“A substantial proportion of hospitals in the first quartile of volume were subsequently excluded for having 10 or fewer cases with each condition,” the authors wrote.
For MI, 734,972 patients were included in the analysis. About 10% of hospitals were classified as low volume for MI (17 mean annual patients), 22% as medium volume (70 patients), and 68% as high volume (236 patients). For the 1,324,287 heart failure patients, 13% of hospitals were classified as low volume (42 mean annual patients), 24% as medium volume (157 patients), and 62% as high volume (422 patients). And for the 1,418,252 pneumonia patients, 18% of hospitals were classified as low volume (59 mean annual patients), 26% as medium volume (179 patients), and 56% as high volume (405 patients).
When mortality was compared for low-, medium-, and high-volume hospitals, a jump from a lower category to the next-higher category carried a risk-adjusted odds ratio for 30-day mortality of 0.89 for MI, 0.91 for heart failure, and 0.95 for pneumonia. All three odds ratios were statistically significant.
For each condition, there was a volume threshold above which an increase of 100 patients in the annual volume was not significantly associated with lower 30-day mortality. The threshold was 610 patients for MI, 500 patients for heart failure, and 210 patients for pneumonia, Dr. Ross and his associates reported.
The findings could pave the way for policy makers to “attempt to increase volume at only the smallest-volume hospitals, perhaps by ensuring that small hospitals are not located in proximity to one another” through the use of certificate-of-need regulations or critical-access hospital programs, the authors said.
The study was partly supported by the Centers for Medicare and Medicaid Services and the National Institute on Aging. Several investigators reported financial or other relationships with pharmaceutical firms and insurance companies.