Peri-operative Anemia and Transfusions and Late Mortality in Coronary Artery Bypass Patients

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Background: Peri-operative anemia and transfusions are associated with adverse operative outcomes after coronary artery bypass grafting (CABG). Their individual association with long-term outcomes is unclear.

Methods: CABG patients 65 and older in the Society of Thoracic Surgeons Adult Cardiac Surgery Database (STS ACSD) (N=504,596; 2011-2018) were linked to Centers for Medicare and Medicaid Service (CMS) data to assess long-term survival. The association of intra-operative anemia defined by nadir intra-operative hematocrit (nadir-Hct) and red blood cell transfusions (RBC-transfusion), and their interactions on long-term mortality were assessed with Kaplan-Meier estimates and multivariable Cox regression. Restricted cubic splines were used to explore the association between nadir-Hct as a continuous variable and long-term mortality.

Results: 258,398 on-pump CABG STS ACSD patients surviving the peri-operative period were linked to CMS. 41% had pre-operative anemia per World Health Organization criteria. Mean intra-operative nadir-Hct was 24%. RBC-transfusion rate was 43.7%. Univariable analysis associated both RBC-transfusion and lower nadir-Hct with worse survival. Lower nadir-Hct was only marginally associated with risk-adjusted mortality: adjusted hazard ratio (AHR) (95%CI)=1.04(1.01-1.06) and 1.07(1.00-1.14) at nadir-Hct=20% and at nadir-HCT=14%, respectively. RBC-transfusion were associated with significantly higher adjusted mortality irrespective of timing of transfusion [AHR(95%CI): AHR(IntraOp)=1.21(1.18-1.27); AHR(PostOp)=1.26(1.22-1.30); AHR(Both)=1.46(1.40-1.52) and across all levels of nadir-Hct. RBC-transfusion was not associated with improved survival at any level of nadir-Hct.

Conclusions: In Medicare CABG patients, RBC-transfusions were associated with increased risk-adjusted late mortality across all levels of nadir-Hct while intra-operative anemia was only marginally so. Tolerance of lower intra-operative nadir-Hct than currently accepted may be preferable to transfusions.