Red blood cells and mortality after coronary artery bypass graft surgery: an analysis of 672 operative deaths

Background: Prior studies have implicated transfusion as a risk factor for mortality in coronary artery bypass graft surgery (CABG). To further our understanding of the true association between transfusion and outcome, we specifically analyzed the subgroup of patients who died after undergoing CABG.

Methods: A total of 34,362 patients underwent isolated CABG between January 2008 and September 2013 and were entered into a statewide collaborative database; 672 patients (2.0%) died and form the basis for this study. Univariate analysis compared preoperative and intraoperative variables, as well as postoperative outcomes, between those with and without transfusion in both unadjusted cohorts and those matched by predicted risk of mortality (PROM). Mortality was further evaluated with phase of care analysis.

Results: Of the 672 deaths, 566 patients (84.2%) received a transfusion of red blood cells. The PROM was 7.5% for the transfused patients versus 4.3% for those not transfused (p < 0.001). Transfused patients were older, more often female, had more emergency, on-pump, and redo procedures, and had a lower preoperative and on-bypass nadir hematocrit. Most other demographics were similar between the groups. Postoperatively, transfused patients were ventilated longer, had more renal and multisystem organ failure, and were more likely to die of infectious and pulmonary causes after longer intensive care unit and overall lengths of stay.

Conclusions: Significant differences in PROM and the postoperative course leading to death between those with and without transfusion suggest the role of transfusion may be secondary to other patient-related factors. Recognizing that the relationship between transfusion and outcome after CABG remains incompletely understood, these findings are suggestive of a complex interaction of many variables.