Hospital procedure volume does not predict acute kidney injury after coronary artery bypass grafting—a nationwide study

Background Acute kidney injury (AKI) is common after coronary artery bypass grafting (CABG) and is associated with poor outcome. Increased hospital procedure volume has been associated with better outcomes. However, the impact of hospital CABG volume on AKI needing dialysis (AKI-D) is less clear. We designed this study to examine (i) the impact of number of annual CABG procedures per hospital (CABG-vol) on AKI-D and inpatient mortality and (ii) if it modifies the relationship between AKI-D and mortality. Methods Using the Nationwide Inpatient Sample database from 2000 to 2010, we identified admissions with CABG and those with AKI-D using International Classification of Diseases, Ninth Revision, Clinical Modification codes. Multivariable logistic regressions were used to assess the impact of CABG-vol on AKI-D and mortality. We used restricted cubic splines to account for the nonlinear relationship between CABG-vol and mortality. We also evaluated the a priori interaction term between CABG-vol and AKI-D in the model for mortality. Results Of 4 002 730 hospitalizations for CABG, 0.7% (24 126) had AKI-D. On adjusted analysis, CABG-vol did not correlate with odds of developing AKI-D [odds ratio (OR) 0.99; 95% confidence interval (CI) 0.99-1.00] but was associated with mortality, though the association was nonlinear. AKI-D was a significant predictor of mortality with OR 7.58 (95% CI 6.81-8.44). The interaction of CABG-vol and AKI-D was not significant (P = 0.8). Conclusions Lower annual CABG hospital procedure volume is significantly associated with higher mortality but not with a higher incidence of AKI-D. AKI-D is associated with higher mortality in those undergoing CABG. However, there is no differential effect of hospital volume on odds of mortality due to AKI-D.