Impact of On-Bypass Red Blood Cell Transfusion on Severe Postoperative Morbidity or Mortality in Children

Children undergoing cardiac surgery are frequently exposed to red blood cell (RBC) transfusions mainly in the case of hemorrhage or low oxygen transport. However, in this population, RBCs are sometimes added to the cardiopulmonary bypass (CPB) priming solution to maintain a predefined hematocrit on bypass. In this study, we investigated the impact of RBCs added to the CPB on severe postoperative morbidity or mortality.

This retrospective cohort study was conducted between 2006 and 2012 in a tertiary care level, children's hospital. Children receiving red cells only to prime the CPB (CPB transfusion) were compared with those receiving no RBCs during their entire hospital stay. The primary outcome was severe postoperative morbidity or mortality. Studied secondary outcomes were neurologic deficit, infection, length of mechanical ventilation, pediatric intensive care unit and hospital length of stay, and mortality. Both groups were compared with propensity score analysis where patients were matched via a genetic matching algorithm. In all analyses, applying a Bonferroni correction, a P value <.05/8 = .00625, was considered statistically significant.

Among the 854 patients retained for this study, 439 (51.4%) received no RBC transfusion during their entire hospital stay and 415 (49.6%) received a CPB transfusion. Thirty-five (8.0%) patients in the no-transfusion group and 110 (26.5%) patients in the CPB transfusion group developed severe postoperative morbidity or died. This difference was statistically significant using univariate analysis (P < .001). Propensity score analysis showed that 79 (19.55%) patients developed severe postoperative morbidity or died in the no-transfusion group compared with 103 (25.50%) patients in the CPB transfusion group (P = .043). The relative risk and its Bonferroni-corrected confidence interval was 0.77 (0.53-1.10). All secondary outcomes were not significantly different between both groups, except the number of patients who developed infections (P < .001).

In the condition of our study, adding RBCs to the CPB priming to maintain a predefined hematocrit does not seem to impact markedly severe postoperative morbidity or mortality in children undergoing cardiac surgery. Only the risk of infection was increased in the CPB transfusion group. Further studies are warranted to better understand the complex interaction among severity of illness, anemia, RBCs transfusion, and outcome in children undergoing cardiac surgery.