title: Impact of patient risk on the hospital volume-outcome relationship in coronary artery bypass grafting.
abstract: BACKGROUND
  The impact of surgical risk on the relationship between hospital volume and outcomes in coronary artery bypass grafting (CABG) is uncertain. We assessed (1) whether in-hospital mortality rates differ across lower- and higher-volume hospitals by expected surgical risk and (2) whether high-risk patients are more likely to undergo CABG at low-volume centers.
  
  
  METHODS
  We used clinical data on 27,355 adults who underwent CABG at 68 hospitals in California between 1997 and 1998. Hospitals were divided into low-volume (n=44), medium-volume (n=19), and high-volume (n=5) categories on the basis of tertiles of annual CABG volume. Using hierarchical logistic regression and log-binomial regression models, we assessed for differences in in-hospital mortality rates across hospital volume categories and the likelihood of CABG being performed in each hospital volume category after adjusting for expected surgical risk.
  
  
  RESULTS
  Differences in adjusted in-hospital mortality rates between low- and high-volume centers rose as the expected risk of in-hospital death increased: 0.8% vs 0.4% at the 20th risk percentile and 3.8% vs 2.5% at the 80th risk percentile (P<.001 for all comparisons). While a similar trend was seen between medium- and high-volume centers, absolute differences were substantially smaller. The likelihood of patients having surgery at a low-volume center also rose significantly with expected surgical risk (relative risk of undergoing CABG at a low-volume center for patients at 80th vs 20th risk percentile, 1.29 [95% confidence interval, 1.14-1.51; P<.001]).
  
  
  CONCLUSIONS
  High-risk patients are more likely to undergo CABG at low-volume facilities where their risk of dying is higher.
authors.affiliation: Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, 48109-0366, USA. bnallamo@umich.edu
authors.forename: Brahmajee K
authors.initials: BK
authors.lastname: Nallamothu
authors.forename: Sanjay
authors.initials: S
authors.lastname: Saint
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Hofer
authors.forename: Sandeep
authors.initials: S
authors.lastname: Vijan
authors.forename: Kim A
authors.initials: KA
authors.lastname: Eagle
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Bernstein
mesh_terms: D000368:Aged; D002140:California / Q000453:epidemiology; D001026:Coronary Artery Bypass / Q000401:mortality* / Q000706:statistics & numerical data*; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D008297:Male; D017063:Outcome Assessment, Health Care; D012044:Regression Analysis; D018570:Risk Assessment; D013503:Surgery Department, Hospital / Q000592:standards* / Q000706:statistics & numerical data*