Storage time of red blood cell concentrates and adverse outcomes after cardiac surgery: a cohort study

Stored red blood cells undergo progressive structural and functional changes over time. Recently, concerns have been raised about the transfusion of older red blood cell (RBC) concentrates after cardiac surgery. The objective of the study was to test the hypothesis that longer storage time of RBCs increases the risk of adverse outcome after cardiac surgery. This is a retrospective cohort study which includes patients who underwent coronary artery bypass surgery and/or valve surgery. All patients were operated in the period from September 2006 to December 2010 and received 1 to 6 units of RBCs intraoperative or after surgery. Patients were divided into two groups according to the storage time of the RBCs. The "younger" group comprised patients who received RBCs ≤14 days old (n = 111) and the "any older" group comprised patients who received RBCs >14 days old (n = 710). Using univariable and multivariable regression analysis, we examined the effect of storage time on the primary composite endpoint of death, myocardial infarction, and stroke (major adverse cardiovascular events). Secondary outcomes were prolonged ICU and hospital stay. Data of 821 patients who received a total of 2,004 RBCs were analyzed. The median storage time for the younger group was 13 ± 2 days, the median storage time for the "any older" group was 21 ± 5 days. The incidence of the primary outcome was 8.6 % in the "any older" group and 4.5 % in the younger group (adjusted odds ratio (OR) 1.68; 95 % confidence interval (CI), 0.65-4.34). Prolonged ICU stay was 12.3 % in the "any older" group and 6.3 % in the younger group (adjusted OR 1.58; 95 % CI, 0.69-3.66). In patients undergoing cardiac surgery, transfusion of RBCs stored for more than 2 weeks was not associated with adverse outcomes.