Extracorporeal membrane oxygenation (ECMO) is a therapy used in severe cardiopulmonary failure. Blood is pumped through an artificial circuit exposing it to nonphysiologic conditions, which promote platelet activation and coagulation. Centrifugal pumps used at lower flow rates than their design point may lose pump efficiency and increase the risk of hemolysis. In this study, thrombogenic properties of two ECMO pumps designed for adult and neonatal use were evaluated using simulations in different flow scenarios. Three scenarios, adult pump in adult mode (4 L/min), adult pump in baby mode (300 ml/min), and neonatal pump used in its design point (300 ml/min), were simulated using computational fluid dynamics. The flow was numerically seeded with platelets, whose activation state was computed considering the stress history that acted along their respective path lines. Statistical distributions of activation state and residence time were drawn. The results showed that using the adult pump in baby mode increased the fraction of platelets with higher activation state confirming that low-pump flow rate impacts thrombogenicity. The neonatal pump showed a backflow at the inlet, which carried platelets in a retrograde motion contributing to an increased thrombogenic potential compared with the adult mode scenario.

Extracorporeal membrane oxygenation is a life saving therapy used in case of acute respiratory/circulatory failure. Exposure of blood to non-physiological surfaces and high shear stresses is related to hemolytic damage and platelet activation. An investigation of the flow structures developing in a conventional single-staged drainage cannula was performed with cross-validated computational fluid dynamics and particle image velocimetry. The aim was to quantify the variation in drainage performance and stress levels induced by different fluid models, hematocrit and vessel-to-cannula flow rate ratios. The results indicated that the 90◦ bends of the flow through the side holes created a recirculation zone potentially increasing the residence time and flow structures developing inside the cannula resembling a jet in a crossflow. The use of different hematocrits did not induce a considerable effect on the drainage performance, with the most proximal set of holes from the tip draining the largest fraction of fluid. However, different flow rate ratios altered the flow rate drained through the tip. The use of 2D data led to a 50% underestimation of shear rate levels, and a Reynolds-number scaling was applied to capture the velocity profiles and flow rates through the side holes.

Extracorporeal membrane oxygenation is a life-saving support therapy in the case of cardiopulmonary refractory failure. Its use is associated to complications due to the presence of artificial surfaces and supraphysiological stress conditions. Thus, knowledge of the fluid structures associated to each component can give insight into sources of blood damage. In this study, an experimentally validated numerical study of a conventional lighthouse tip cannula in return configuration was carried out to characterize the flow structures using water or a Newtonian blood analog with different flow rate ratios and cannula positioning and their influence on hemolysis. The results showed that strong shear layers developed where the jets from the side holes met the co-flow. Stationary backflow regions at the vessel wall were also present downstream of the cannula. In the tilted case, the recirculation was much more pronounced on the wide side and almost absent on the narrow side. Small vortical backflow structures developed at the side holes which behaved like obstacles to the co-flow, creating pairs of counter-rotating vortices, which induced locally higher risk of hemolysis. However, global hemolysis index did not show significant deviations. Across the examined flow rate ratios, the holes on the narrow side consistently reinfused a larger fraction of fluid. A radial force developed in the tilted case in a direction so as to recenter the cannula in the vessel.

Extracorporeal membrane oxygenation is a life-saving treatment used insevere cardiac/lung failure. The occurrence of non-physiological stresses and thepresence of artificial surfaces gives rise to complications as thrombus formationand hemolysis. While CFD can be a powerful tool to assess risks associatedto mechanical stresses, the use of models to compute blood flow and predictblood damage entails uncertainties on the results that need to be quantified. Inthis work, the geometry of a ECMO return cannula in a shifted position wasused as a benchmark to evaluate the effects of model coefficients for hemolysiscomputation and the effect of different types of viscosity modelling at differenthematocrits. The results showed that the largest uncertainty was induced bythe chosen model coefficients, with variability of up to two orders of magnitude.Using a Newtonian analog led to similar global hemolysis indices compared toa non-Newtonian model, if the viscosity value was based on the asymptoticviscosity of the non-Newtonian model. Considering the local values of hemolysis,differences were observed in stagnation areas, with variations of more than 50%.The inclusion of a simple red blood cell transport model did not significantlyaffect time-averaged results, but it introduced larger time variability.

Extracorporeal life support (ECLS) are life-saving therapies used to supportcardiac and pulmonary functions in severe failure. In recent years the use ofcentrifugal pumps to drive the flow has become increasingly common. Severaldesigns are available on the market with different certified operating ranges.The use of centrifugal pumps in low flow conditions has been shown to increasehaemolytic and thrombogenic risks and been linked to the appearance of aretrograde flow at the inlet pipe. In this study, an experimental investigation ofseveral pump designs has been performed to assess the occurrence of backflowacross different operating conditions. Numerical simulations have been carriedout for a geometry and flow case showing backflow to highlight flow structuresassociated to it. The results showed that covered pumps were more likely toexhibit backflow in low flow conditions. The appearance of backflow was linkedto the development of vortical structures rising from the impeller blade tip andrising, being trapped between the shroud and the pump housing.