Preface to the special series “Blood Transfusion Practice in ECMO Patients”

Extracorporeal membrane oxygenation (ECMO) was developed as a closed-circuit modification of cardiopulmonary bypass, which involves draining blood from the venous circulation, pumping it through an oxygenator, and returning it to either the venous or arterial circulation (1). The main circuit difference is the lack of a reservoir, which does not allow the continuous adaptation of the blood volume to the flow requested by changes in the patient’s condition (2). As a consequence, the blood volume and the red cell mass available within the requested blood flow are particularly interdependent, and oxygenation, decarboxylation, and cardiac failure support are needed. Moreover, ECMO practice is hampered by the need for anticoagulation to respond to the continuous activation of the coagulation-inflammation pathway determined by the contact of the blood with the extracorporeal surface. The frequent occurrence of bleeding, which seems to have multifactorial origins (patient condition, underlying disease and concomitant circumstances, anticoagulation, coagulopathy, and circuit interaction), further complicates the situation (3).

In the first chapter, Pacheco-Reyes and colleagues tackle the topic of anticoagulation. To discuss blood product transfusion comprehensively, we started with a review of the changes undergone by the circulating blood (4). ECMO practice is a continuous balancing act between difficult and extreme conditions. The circuit-blood interaction increases the clotting risk, which can be mitigated by adequate anticoagulation therapy, though this prophylactic measure may significantly increase the risk of bleeding. Finally, although thrombotic events are more common, bleeding events carry a higher risk of in-hospital mortality (3).

Next, Kowalewski and colleagues (5) describe the current state of blood product transfusions within the ECMO setting. Despite effective oxygenation and maintenance of end-organ perfusion, mechanical shear forces, bleeding risk and hemodilution during ECMO necessitate a significant amount of blood product. Kowalewski’s group collated all existing data regarding transfusions of packed red blood cells (pRBCs), platelets, fresh frozen plasma, and cryoprecipitate across centers. In general, transfusions should consider oxygen-carrying capacity, thrombocytopenia, and factor deficiencies. It also remains unclear if transfusion is correlated with ECMO prognosis and primary patient outcomes, given the close association between the clinical picture and transfusion needs (5). Globally, there remains a lack of consistent indications for transfusion and large variations in blood product administration (6,7).

To address the debate over thresholds for blood product transfusion and the lack of specific guidelines, Siragusa and colleagues attempt to find a solution (8). Different guidelines for hemoglobin thresholds and coagulopathy have been proposed in the literature, but there is no clear consensus on how to reconcile these recommendations. The group proposes a restrictive approach to RBC transfusion, maintaining hemoglobin between 7 and 9 g/dL and careful consideration of the balance of pro- and anticoagulation factors on an individual patient basis during ECMO transfusion. Recognizing rare acute adverse effects of transfusion, including hemolysis, lung injury, and circulatory overload, remains an important issue in the transfusion discussion (8).

In the following chapter, Elmelliti and colleagues focus specifically on non-RBC products to provide clarity and efficacy in the transfusion of platelets, fresh frozen plasma, and cryoprecipitate (9). Viscoelastic testing and thromboelastography may play a pivotal role in the assessment of coagulation in ECMO over traditional coagulation tests, driving the dynamic transfusion of blood products or antifibrinolytics. The authors consider that appropriate management of non-RBC transfusion requires careful consideration of circuit priming and frequent laboratory tests to ensure safe therapeutic ranges.

Maldarelli et al. then present an insight into the role of RBCs in the ECMO setting, both as a function of the carrying capacity of the circuit and the goal of end-organ perfusion in critically ill patients (10). Within this chapter, bleeding and thrombosis in ECMO patients are discussed with respect to consumptive coagulopathy and hemolysis and the difference in true oxygenation between veno-arterial (VA) and veno-venous (VV) ECMO. Maldarelli’s group contends that these factors necessitate a tailored approach centered on the Extracorporeal Life Support Organization (ELSO) hematocrit standard, but also consideration of the patient’s clinical picture. Additionally, this analysis sheds light on the age of RBCs as a factor in transfusion outcomes to better elucidate the effect on ECMO, with a lower age of transfused RBCs showing more of a theoretical than a practical benefit.

Next, our group surveyed the literature both for indications for ECMO to gain greater insight into the heterogeneity of the hemodynamic requirements of patients receiving ECMO and for the subsequent triggers for transfusion (11). The varying characteristics of patient populations can create discordance in pRBCs transfusion protocols between different centers and clinicians. This chapter draws a distinction between the conventional uses of transfusion for ECMO, such as acute respiratory distress syndrome (ARDS), where a restrictive blood product transfusion is preferred, and more complex situations, like concomitant sepsis and pregnancy, where liberal strategies may be preferred.

In the final chapter of this series on blood transfusion in the ECMO patient, we attempt to take a more expansive perspective on the feasibility of hemoglobin thresholds for blood product transfusion, as well as strategies that can potentially lower the requirement for transfusions (12). In addition to hemoglobin, it may be more therapeutic to administer blood products only when oxygen-carrying capacity and gas exchange are significantly compromised. Due to the practice pattern variation that currently exists, some practitioners may prefer to maintain end-organ perfusion and reduce ischemia, while others favor more restrictive transfusion requirements to minimize long-term mortality and complications while the patient receives ECMO in a critical care setting.

In summary, this series on blood transfusion in ECMO patients provides a broad and detailed study of the pathophysiological and clinical aspects of transfusions during ECMO. It also attempts to address the wide cross-center variation in blood product transfusion practices, drawing on a wide range of clinical expertise and perspectives. As Guest Editors, we are very grateful to the experts for their invaluable contributions and willingness to share their knowledge and expertise. We trust the multifaceted view of the topic will be useful in clinical and educational practice, promoting the rational use of the scarce but essential resource represented by blood products.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Annals of Blood for the series “Blood Transfusion Practice in ECMO Patients”. The article did not undergo external peer review.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://aob.amegroups.com/article/view/10.21037/aob-2024-02/coif). The series “Blood Transfusion Practice in ECMO Patients” was commissioned by the editorial office without any funding or sponsorship. G.M. served as the unpaid Guest Editor of the series. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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