Factor XII Deficiency in ECMO Patients

Background: Extracorporeal membrane oxygenation (ECMO) for cardiopulmonary support of critically ill patients is used frequently in the pediatric and adult population. Although a lifesaving modality, it is burdened with high morbidity and mortality as a result of hematologic complications (Dalton, et al. Am J Respir Crit Care Med. 2017). Bleeding and thrombosis are related to contact of blood and its cellular components with the non-biologic surface of the extracorporeal circuit used that results in a massive inflammatory and clotting response. Factor XII deficiency is not associated with bleeding, but results in a significant prolongation of conventional coagulation assays making them unreliable for monitoring. Here we discuss 3 cases of Factor XII deficiency and the implications it has on monitoring anticoagulation in patients on ECMO. Laboratory characteristics for all 3 patients are outlined in Table 1. Case 1: Newborn full-term male with persistent pulmonary hypertension (PPHN) and meconium aspiration syndrome (MAS) with respiratory failure was placed on ECMO support on day of life 1. Patient received several units of cryoprecipitate and fresh frozen plasma (FFP) to correct deficiencies throughout his 31 day ECMO course. Patient did not have any bleeding or thrombotic complications, however he showed no improvement in lung function and decision was made to discontinue ECMO support. Case 2: Newborn full-term male with severe hypoxic ischemic encephalopathy (HIE) and MAS with secondary PPHN required ECMO support on day of life 1. His Factor XII level normalized with replacement by FFP and was decannulated after 11 days of ECMO support. This patient was discharged home with family in stable condition at 5 weeks of age. Case 3: 20-year-old female with history of recurrent astrocytoma, chronic lung disease, hydrocephalus with ventriculoperitoneal (VP) shunt, and tracheostomy presented with multifocal pneumonia and suspected sepsis. Despite fluid resuscitation and ventilatory management patient continued to have hypotension and hypoxia and thus was placed on ECMO. Prior to cannulation, patient was noted to have a coagulopathy. In addition, Factor II was low at 57% and corrected with one unit of FFP; which was thought to be related to consumptive process. On ECMO day 8, she had worsening hypotension despite vasopressor support and fixed and dilated pupils; suspected to have thromboembolic stroke and thus decision was made to withdraw life support. Discussion: Adequate anticoagulation in patients with Factor XII deficiency requiring ECMO support presents a challenging task. Patients with Factor XII deficiency generally do not show symptoms of a bleeding disorder, which may lead to misinterpretation of coagulation assays (Kokoye, et al. Thromb Res 2016). Increased contact activation inside the ECMO cannula causes activation of platelets, consumption of Factor XII, and formation of FXIIa-antithrombin complexes that may contribute to increased risk for thrombus formation (Kokoye, et al. Thromb Res 2016 and Bachler, et al. J Thromb Thrombolysis 2019). All patients had Factor XII levels <40% on initial testing, which is sufficient to cause severe changes to the aPTT. A circulating anticoagulant aPTT was completed to assess for presence of lupus anticoagulants in 2 of the patients, which has been known to falsely elevate the aPTT and was negative (Bachler, et al. J Thromb Thrombolysis 2019). All patients received FFP in an attempt to correct deficiency and facilitate the use of aPTT and ACTs for monitoring. However, this did not prove to be successful in 2/3 patients despite receiving adult plasma. Hepzyme TEGs showed improvement in R-time post-FFP in 2 patients, but in 1 there remained evidence of factor deficiency. It is clear that traditional coagulation assays, including aPTT and ACT, become unreliable and the R-time on TEG becomes difficult to dissect heparin versus coagulation factor effect. We recommend attempting to correct factor deficiency with FFP to potentially decrease risk of thrombotic complications, and choosing an alternative laboratory monitoring assay for heparin, such as Anti-Xa levels, which may more accurately correspond to the anticoagulation status in this population. Currently, we are running a modified thrombin generation assay in these Factor XII deficient patients, pre/post-FFP, to identify if there is a decrease in thrombin generation post-FXII/FFP supplementation. Table 1 Disclosures Chitlur: Bayer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda/Shire: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bioveritiv/Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; CSL-Behring: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agios: Research Funding; Octapharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novo Nordisk Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Serine Proteases Of Coagulation Modulate Tissue Factor Expression and Monocyte-Induced Thrombin Generation

Background As part of their role in immune response and inflammation, monocytes exhibit a potent procoagulant phenotype which is mediated by Tissue Factor (TF), the main trigger of coagulation. TF expression by monocytes is induced by various agonists such as lipopolysaccarides (LPS) and proinflammatory cytokines. We recently reported that Factor Xa could induce TF expression (Ben-Hadj–Khalifa J Thromb Thrombolysis 2011). The aim of the present study is to evaluate, in a model of highly purified human monocytes, the effect of 2 major serine proteases, namely factor VIIa, which activates Xa, and activated Protein C (APC), which inhibits thrombin generation but also exerts potent cytoprotection. Methods Human monocytes were purified by elutriation of cytapheresis material obtained from healthy donors. Informed consent was obtained. Cell viability (trypan blue-negative cells) was > 98%, the quality of elutriation was estimated by the percentage of CD14+ cells (> 95 %). Monocytes (5.106 cells/mL) were activated for 5 h, by FVIIa (0.1, 0.4, 2 µM, Novo Nordisk) or APC (30. 50, 100 nM, Diagnostica Stago) at 37°C in a 5% CO2 humidified atmosphere. FXa (0.025 U/mL, Diagnostica Stago) was used as a positive control. TF expression was studied using real-time RT-PCR, Western Blotting (WB), and thrombin generation assay (TGA). Our experimental conditions have previously been reported (Ben-Hadj–Khalifa J Thromb Thrombolysis 2011). Results 1) FVIIa : TF mRNA and protein were not detected in response to FVIIa. FVIIa-activated monocytes supported thrombin generation. However, the kinetics of thrombin generation was slow compared with FXa (table 1). 2) APC : Monocytes dose-dependently expressed TF mRNA and protein in response to APC, with a complete agreement between RT-PCR and WB. APC-stimulated monocytes supported a strong thrombin generation, in a dose-dependent manner. The expression of TF in response to APC was consistently higher than in response to FXa, whatever the assay (figure 1) Discussion / Conclusion The effect of FVIIa and APC on monocyte TF expression has never been previously reported. We could not demonstrate the ability of FVIIa to induce TF expression. However, these experiments were performed in the absence of exogenous TF. As it is reported that FVIIa activates PARs inside the complex FVIIa-TF, or FVIIa-TF-FXa (Rollin Hematologie 2012, Camerer J Cell Biology 2000), we will repeat the experiments in the presence of TF. Unexpectedly, whereas we failed to detect TF expression in RT-PCR and WB, we observed an effect of VIIa on monocyte-induced thrombin generation. It raises the question of the dependency towards TF expression of our model. We report for the first time that APC is a strong inducer of TF expression by monocytes. This observation is unexpected since APC is a major coagulation inhibitor and cytoprotective. The expression of TF is currently associated with cell activation or apoptosis induction. The cytoprotective effect of APC has been described for endothelial cells and macrophages, but with different pathways for the activation of PAR-1, which is Endothelial Protein C Receptor (ECPR)-dependent in endothelial cells and CD11b/CD18 dependent for macrophages (Van de Poll, Current Opin Infections Des 2011). Interestingly, monocytes not only express PAR-1 and b2 integrins, but also EPCR and thrombomodulin (TM), the endothelial cofactor of thrombin, for the activation of PC. Further investigations including signaling pathway studies are required to elucidate this paradigm. Disclosures: No relevant conflicts of interest to declare.