Investigation of Shear Induced Clot Formation in Extracorporeal Membrane Oxygenation: Computer Based Flow and Clot Evaluation

Extracorporeal membrane oxygenation (ECMO) is associated with hemostatic complications, posing great risk on the patients. However, the underlying clotting mechanisms are not yet fully understood to sufficiently prevent clotting in clinical practice. Aim of this work was to gain deeper insights into the complex clotting phenomena. Clotting was investigated with state-of-the-art visualization protocols for seven clinically used membrane lungs (MLs), CFD of realistic fiber mat stacks, and non-invasive flow measurements within ECMO pumps. A polymer embedding procedure was established to analyze fiber mat spanning immunological deposits inside MLs and ECMO pumps, expanding the histological repertoire. A significant higher clot volume was observed in the first chamber of all MLs. Clot deposition was constant along the fiber mats. However, in vicinity of structural changes (e.g. dividing wall) an irregular clot volume was observed. CFD results proved that the asymmetrical hollow-fiber arrangement clearly affects the local flow regimes. Yet, pathological flow, in terms of vWF elongation was not found. In contrast, the pump was associated with a turbulent flow regime. In conclusion, intra-device clot formation remains a complex phenomenon. It seems likely that the pump is a main trigger of clot formation. The local flow regimes close to the hollow-fibers result in elevated shear stress but not above the critical threshold defined in the literature. However, flow induced clotting might still be prevailing close to structural changes inside the ML.