In this study, washing RBC and platelets transfused to children undergoing open heart surgery reduced post-operative inflammatory biomarkers. Subjects transfused with washed blood had significantly lower post-operative IL-6 levels and lower IL-6:IL-10 ratios than subjects receiving unwashed blood, consistent with a more favorable inflammatory profile. As previous work has demonstrated, higher IL-6 levels are associated with greater illness severity, longer length of hospital stay, sepsis and death (61
), although not powered to assess for clinical outcomes, we believe our results may have clinical implications. This is supported by the fact that IL-6 levels are known to rise following CPB (62
) and correlate with postoperative morbidity (65
). Furthermore, in pediatric patients following CPB, postoperative IL-6 levels correlate with length of inotropic support, mechanical ventilation, and increased oxygen requirement (66
), and patients undergoing the most complex surgeries have the highest levels of IL-6 (67
In this series, IL-10 levels immediately off CPB were numerically but not significantly higher in subjects receiving washed blood compared to those receiving unwashed blood. These results are consistent with an improved inflammatory balance as IL-10, an anti-inflammatory cytokine (68
), stimulates the compensatory anti-inflammatory response syndrome (69
), with elevated levels correlating with adverse clinical outcomes including multiple organ dysfunction, sepsis (70
) and mortality (73
). Interleukin-10 levels are known to rise following pediatric cardiac surgery with CPB (75
). In this study, IL-10 levels were lower 6 and 12 hours post-CPB in subjects receiving washed blood, likely due to lower IL-6 levels at those time points, requiring a less vigorous compensatory response.
Similar to our study, Bilgin et al
2010 studied the effect of leukocyte-depleted RBC transfusions on postoperative inflammatory mediators and postoperative complications in 346 adults undergoing cardiac valve surgery (78
). Increased concentrations of IL-6 and IL-12 occurred in subjects receiving leukocyte-containing RBCs, and higher IL levels were measured in those subjects developing postoperative infections and multiple organ dysfunction. Multivariate analysis demonstrated an association between elevated IL-6 concentration and multiple organ dysfunction and hospital mortality. They conclude that leukocyte-containing RBCs adversely affect the postoperative proinflamatory response, and may affect postoperative complications.
Our results indicate that, in addition to leukoreduction, further modification of stored blood cells with the removal of residual leukocytes and bioactive substances by washing, decreases the inflammatory response in the recipient. Whether this may lead to improved clinical outcomes warrants further study. Additionally, the effect of RBC storage duration requires consideration. It has been hypothesized that “older” RBCs are more likely to be associated with adverse clinical outcomes than “fresh” blood (79
). We believe that it is the bioactive mediators in the supernatant of older RBC that is likely responsible for the proinflammatory (and potential clinical) impact on the transfusion recipient. We propose that adverse effects from increased numbers of RBC and component therapy transfusions, and storage duration, may be ameliorated by washing. As neonates and infants undergoing cardiac surgery with CPB receive the largest numbers of RBC and platelet transfusions, we believe they are particularly susceptible to the inflammatory impact of those transfusions, and would benefit most from the washing of those cells.
This study is limited in that it was not powered to test for clinical outcomes. Biomarkers were chosen as primary outcome measures as they are continuous variables (improving power) strongly associated with adverse outcomes. Local patient numbers precluded powering the study for clinical outcomes which would be of greater relevance. It is possible that there is a significant genomic component to the measured biomarkers and children may behave very different clinically, with similar biochemical profiles. Fortunately, the two study groups had similar pre-operative interleukin levels and similar demographics including genetic and comorbid conditions. Larger studies following biomarkers over time, both pre and post-operatively, may help to better delineate the correlation between an individual's biomarker level and their clinical condition. The short term measurements of interleukin levels are a limitation of this study. Serial measurements of interleukin levels over a longer post-operative period would add important information regarding the impact of the transfusion strategy on both laboratory and clinical parameters.
A study with a more homogenous subject population undergoing similar surgeries would be of greater interest, as it would allow for more direct between-group comparisons. As neonates and young infants receive the largest numbers of RBC and platelet transfusions, it would be more rigorous to study only those subjects, and the results would be more powerful with less heterogeneous cardiac defects and surgical procedures. Local subject numbers precluded use of such a restricted study population and would require a multi-center trial. Additional subgroup analysis of subjects undergoing similar cardiac procedures and tests for associations between laboratory measures and clinical outcomes is needed.
Of note, none of the 34 patients who were randomized but did not receive transfusions died, emphasizing, in our view, that transfusion is both a marker for severity of illness/difficulty of surgery, as well as a potentially toxic therapy. Leukoreduction has been proven to reduce the toxicity of transfusion in cardiac surgery (18
), and our results suggest that supernatant removal by washing may have the potential to further reduce the morbidity that follows transfusions in this setting. Preliminary data from a small randomized trial suggests that washed transfusions may improve clinical outcomes in a very different patient population, adults with acute leukemia (48
Furthermore, at the time of study design reviewers and clinicians expressed concern that the time necessary to perform washing procedures would place subjects at risk from delays in receiving necessary blood transfusions (particularly platelets). There was only one subject where active mediastinal tube bleeding was thought to preclude waiting 2 hours for platelets to be washed, resulting in only one such protocol violation in all 164 subjects. The other two protocol violations in fact caused unwashed group subjects to receive washed products due to their increased safety profile. The extremely low rate of protocol violations in this study indicates that the technical challenge and time necessary for washing does not preclude use of washed products even in this critically ill post-operative population.
In this series very few subjects, <3%, required platelet, FFP and/or cryoprecipitate transfusions. This suggests that routine use of these products is unnecessary for achieving excellent results in terms of morbidity and mortality. Indeed, transfusion of these blood components probably carries significant risks. Our local CPB strategy does not include use off FFP in the prime, nor routine use of these pro-hemostatic products on/or coming off CPB, and very few of our patients required such products. Additionally, low numbers of RBC transfusions were utilized in this series when compared to many institutions. The low number of RBC transfusions and platelet transfusions may actually have hindered the detection of a beneficial clinical effect of washing. When larger numbers of RBC and platelet transfusions are given, washing potentially would have greater impact. A similar study performed in a center where larger numbers of RBC and platelet products are transfused, may have produced more striking clinical results.
Two subjects in the unwashed group (but no washed group subjects) required ECMO support, contributing to the larger numbers of total RBC and coagulant product transfusions in the unwashed group. A larger study with more patients on ECMO may demonstrate that the larger volume of blood product transfusions may overwhelm any potential benefit from blood cell modification via washing. However, the significant risk of electrolyte disturbances associated with large volume transfusions prompts washing of blood transfused on ECMO to be performed at many centers. Therefore the “sickest” patients may end up receiving washed blood and future studies may choose to exclude subjects requiring ECMO from data analysis. In the current study when the two ECMO subjects were removed from the analysis the difference between transfusion groups persisted (220 RBC and 14 coagulant product transfusions in the unwashed group v. 202 RBC and 12 coagulant product transfusions in the washed group).
Our results are particularly generalizable as virtually all eligible patients were enrolled over the 23 month period of the study. Data from the current study demonstrate that modification of RBC and platelet transfusions by washing mitigates post-transfusion inflammation and immunomodulation and non-significantly reduced the number of transfusions and donor exposures. Whether these laboratory findings are clinically relevant, and whether they are reproducible in other institutions, remains unknown. Whether the trend towards fewer transfusions in subjects receiving washed blood persists in larger studies would be of great interest, as would be testing for an association with post-operative complications. A large multi-center clinical trial powered for clinical outcomes is warranted. Focus on those subgroups undergoing similar cardiac procedures would add strength to such study. Expansion of clinical trials of washed transfusions to other critically ill patients is warranted by the results of this and previous studies.