Transfusion and postoperative pneumonia in coronary artery bypass graft surgery: effect of the length of storage of transfused red cells

BACKGROUND: Various bioactive substances are released from white cell (WBC) granules into red cell (RBC) components in a time-dependent manner during blood storage. Some of these substances may have immunosuppressive effects and may contribute to transfusion-induced immunomodulation. RBCs transfused after prolonged storage may be associated with a higher incidence of postoperative infections than fresh RBCs. This hypothesis does not seem to have been investigated in a clinical study. STUDY DESIGN AND METHODS: The records of 416 consecutive patients undergoing coronary artery bypass graft operations at the Massachusetts General Hospital were reviewed. The association between the length of storage of the transfused RBCs, as well as the number of units of non-WBC-reduced allogeneic RBCs and/or platelets transfused, and the occurrence of postoperative pneumonia was calculated by logistic regression analyses adjusting for the effects of confounding factors. Among these were the numbers of days of intubation, days of impaired consciousness, and units of RBCs transfused. RESULTS: By Centers for Disease Control and Prevention criteria, pneumonia developed in 54 patients (13.0%). Among 269 patients given RBCs, the risk of pneumonia increased by 1 percent per day of increase in the mean storage time of the transfused RBCs (p<0.005). In an analysis of all patients, the risk of pneumonia increased by 5 percent per unit of non-WBC-reduced allogeneic RBCs and/or platelets received (p = 0.0584). CONCLUSION: After adjustment for the effects of the risk factors for pneumonia and the number of transfused RBCs, an association was observed between the length of storage of transfused RBCs and the development of postoperative pneumonia. This association should be investigated further in future studies of the outcomes of blood transfusion.