PB0264 - Composition of thrombi in pediatric ECMO circuits

Background: Extracorporeal membrane oxygenation (ECMO) is a treatment option for children with severe cardiac and/or respiratory failure. Despite anticoagulant therapy, thrombi regularly develop inside ECMO circuits of children. Thrombi that necessitate change of ECMO circuits can also embolize to the patients. The composition of thrombi inside ECMO circuits is unknown and scarcely investigated. Knowledge of thrombus composition might be helpful in developing targeted antithrombotic strategies to prevent thrombus formation.

Aims: In this pilot study, we aim to investigate the composition of thrombi inside ECMO circuits after clinical use in children.

Methods: After clinical use in pediatric patients ( < 18 years), ECMO circuits were rinsed with buffer solution, visually inspected for thrombi and the location of thrombi was recorded. Thrombi were obtained from connector sites of pump, oxygenator, and oxygenator fibers and processed for paraffin embedding. Thrombi were stained with hematoxylin-eosin and examined via immunohistochemistry for presence of platelets (CD61) and Von Willebrand Factor (VWF). Scanning electron microscopy (SEM) was used to investigate the structures adherent to different surfaces of the circuit.

Results: Fourteen circuits from 11 patients (median age 1 day, 9 neonates, 12 veno-arterial ECMO) were studied. All circuits exhibited thrombi, especially in oxygenator and connection sites. CD61 staining showed platelet rich thrombi at the connection site (Fig 1); SEM showed activated platelets in the oxygenator and protein deposits at connector sites.

Conclusion(s): Despite anticoagulation, platelet rich thrombi develop in all ECMO circuits of pediatric patients, especially at connector sites and in the oxygenator. In this pilot study, a method has been developed to perform several techniques to evaluate the composition of those thrombi. These methods will be extended to VWF staining on additional slides. Pilot data suggest that antiplatelet therapy might be a valuable addition to current anticoagulant therapy.