Background: Veno venous Extra Corporeal Membrane Oxygenation (vvECMO) is associated with frequent hematological ECMO-related complications needing ECMO circuit change. Microvesicles (MVs) interplay during the thrombosis-fibrinolysis process. The main objective of the study was to identify subpopulations of MVs associated with indications of early vvECMO circuit change. Methods: This is a prospective observational monocenter cohort study. Blood gas was sampled on the ECMO circuit after the membrane oxygenator to measure the PO_{2 post oxy} at inclusion, day 3, day 7 and the day of ECMO circuit removal. Blood samples for MV analysis were collected at inclusion, day 3, day 7 and the day of ECMO circuit removal. MV subpopulations were identified by flow cytometry. Results: Nineteen patients were investigated. Seven patients (37%) needed an ECMO circuit change for hemolysis (n = 4), a pump thrombosis with fibrinolysis (n = 1), persistent thrombocytopenia with bleeding (n = 1) and a decrease of O₂ transfer (n = 1). Levels of leukocyte and endothelial MVs were significantly higher at inclusion for patients who thereafter had an ECMO circuit change (p = 0.01 and p = 0.001). The areas under the received operating characteristics curves for LeuMVs and EndoMVs sampled the day of cannulation and the need for ECMO circuit change were 0.84 and 0.92, respectively. PO_{2 post oxy} did not significantly change except for in one patient during the ECMO run. Conclusions: Our pilot study supports the potential interest of subpopulations of microvesicles early associated with hematological ECMO-related complications. Our results warrant further studies.

Background/Objectives: Coronavirus disease 2019 (COVID-19) is associated with immunothrombosis involving endothelial dysfunction and coagulation activation. We aimed to compare biomarkers spanning multiple immunothrombotic pathways between patients with moderate and severe COVID-19 at baseline and according to clinical outcome. Secondary analyses compared biomarker levels at days 3 and 7. Methods: This prospective observational study included 42 hospitalized patients with COVID-19 enrolled between April 2020 and January 2021, comprising 21 with moderate and 21 with severe disease. Biomarkers of coagulation, endothelial dysfunction, endogenous anticoagulant pathways, fibrinolysis, and extracellular vesicle-mediated activity were measured at baseline and on days 3 and 7. The prespecified ventilation/death composite included invasive mechanical ventilation already ongoing at baseline or initiated subsequently and/or death by day 28. Results: Seventeen patients (40.5%) met the composite criterion, including 12 patients already receiving invasive mechanical ventilation at baseline. At baseline, severe disease was associated with higher D-dimer (1.74 [0.87–3.67] vs. 0.68 [0.46–0.94] µg/mL FEU), free tissue factor pathway inhibitor (TFPI; 55.00 [38.00–109.00] vs. 16.00 [14.00–29.00] ng/mL), extracellular vesicle-associated tissue factor activity (EV-TF; 28.86 [13.61–48.72] vs. 5.00 [5.00–5.70] fM), and extracellular vesicle-associated plasmin generation capacity (EV-PGC; 93.36 [41.60–303.10] vs. 24.50 [16.14–35.74] fM; all p < 0.01). Exploratory ROC analyses further illustrated the separation of these biomarker distributions between the predefined clinical groups. Conclusions: Severe COVID-19 and unfavorable outcomes were associated with baseline differences in biomarkers spanning several immunothrombotic pathways, some of which remained detectable at days 3 and 7. Interpretation of the marked TFPI elevation is limited by differences in heparin exposure between severity groups. These exploratory findings require confirmation in larger cohorts, and their incremental value beyond routine clinical assessment remains untested. Outcome analyses largely reflected baseline severity, with only five subsequent events.