Transfusion-related immunomodulation: a second hit in an inflammatory cascade?

Allogeneic blood transfusions are dose-dependently associated with postoperative complications. Leucocytes present in blood components may play a role in these effects, referred to as transfusion-related immunomodulation. Of 19 randomized controlled trials of the effect of allogeneic leucocytes in transfusions, 13 looked into the effect of leucocyte-containing red blood cells (RBCs) in the surgical setting on the occurrence of postoperative infections and/or mortality. In contrast to conflicting outcomes of the trials in other settings, in cardiac surgery there is evidence that leucocyte-containing RBCs increase postoperative complications associated with mortality. The studies performed in cardiac surgery show less heterogeneity than studies in other surgical interventions and had been conducted either in one or a few participating centres. In this review, we discuss possible explanations for these results in cardiac surgery (as opposed to other settings), which may relate to clinical as well as transfusional factors. We suggest that leucocyte-containing transfusions during and after cardiac surgery add a second insult to the cardiopulmonary bypass procedure-induced systemic inflammatory response.