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High-risk patients often undergo bypass surgery at low-volume hospitals where their risk of dying is higher

Several studies have shown that patients who undergo coronary artery bypass graft surgery (CABG) at hospitals that perform a high volume of CABGs have better outcomes. Yet, high-risk CABG patients are more likely to undergo bypass surgery at low-volume hospitals where their risk of dying is higher, according to a recent study supported in part by the Agency for Healthcare Research and Quality (HS11540). Thus, patients who are most likely to benefit from having CABG at high-volume hospitals appear to be least likely to have surgery at such centers.

A possible explanation for this is that current systems for referring high-risk patients to high-volume regional centers are only partially effective, suggest researchers from the University of Michigan Health System and the VA Medical Center in Ann Arbor. In their study, 38 percent of patients at the 80th percentile for risk underwent CABG at a low-volume hospital compared with 28 percent at the 20th percentile for risk.

The researchers used clinical data on 27,355 adults who underwent CABG at 68 hospitals in California between 1997 and 1998. They divided hospitals into low-, medium-, and high-volume categories on the basis of tertiles of annual CABG volume. After adjusting for expected surgical risk and other factors, differences in inpatient mortality rates between low- and high-volume centers rose as the expected patient risk of in-hospital death increased: 0.8 percent vs. 0.4 percent at the 20th risk percentile and 3.8 percent vs. 2.5 percent at the 80th risk percentile. The likelihood of patients having surgery at a low-volume center also rose significantly with expected surgical risk. Patients at the 80th risk percentile had 29 percent greater relative risk of undergoing CABG at a low-volume center than patients at the 20th risk percentile.

More details are in "Impact of patient risk on the hospital volume-outcome relationship in coronary artery bypass grafting," by Brahmajee K. Nallamothu, M.D., M.P.H., Sanjay Saint, M.D., M.P.H., Timothy P. Hofer, M.D., M.Sc., and others, in the February 14, 2005, Archives of Internal Medicine 165, pp. 333-337.

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