Objectives: The aim of this study was to compare long-term mortality in patients undergoing primary isolated coronary artery bypass grafting who received ≥1 units of red blood cells (RBCs) or no RBCs. We hypothesized that a possible difference in long-term mortality was due to preoperative morbidity and/or postoperative morbidity.
Methods: This prospective cohort study, part of the Cardiac Surgery Outcome Study (CaSOS) at St. Olavs University Hospital, Trondheim, Norway, included patients operated on from 2000 through 2014 (n = 4014) and excluded those with large intra- or postoperative blood loss or 30-day mortality. Observed mortality from 30 days to 15 years postoperatively was compared between patients who received RBC transfusion and those who did not. Cox regression analysis was performed with unadjusted models, adjusting for pre- and intraoperative covariates, and with further adjustment for postoperative complications. Sensitivity analyses were performed with propensity score matching or including 30-day mortality.
Results: The unadjusted hazard ratio (HR) for long-term mortality was 2.10 (1.81-2.43; P < 0.01) for transfused patients. After adjusting for pre- and intraoperative variables, the HR was 1.26 (1.04-1.53; P = 0.02). With further adjustment for postoperative complications, RBC transfusion was no longer significant and the HR was 1.19 (0.98-1.44; P = 0.08). These results were supported by the sensitivity analyses.
Conclusions: The study indicated that most of the association between RBC transfusion and long-term mortality following primary isolated coronary artery bypass grafting was due to confounders, especially from postoperative complications.