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Venovenous extracorporeal membrane oxygenation is used for respiratory support in the most severe cases of acute respiratory distress syndrome. Blood is drained from the large veins, oxygenated in an artificial lung, and returned to the right atrium (RA). In this study, we have used large eddy simulations to simulate a single-stage "lighthouse" drainage cannula in a patient-averaged model of the large veins and RA, including the return cannula. We compared the results with previous experimental and numerical studies of these cannulas in idealized tube geometries. According to the simulations, wall proximity at the drainage holes and the presence of the return cannula greatly increased drainage through the tip (33% at 5 L/min). We then simulated a multi-stage device in the same patient-averaged model, showing similar recirculation performance across the range of extracorporeal membrane oxygenation (ECMO) flow rates compared to the lighthouse cannula. Mean and maximum time-averaged wall shear stress were slightly higher for the lighthouse design. At high ECMO flow rates, the multi-stage device developed a negative caval pressure, which may be a cause of drainage obstruction in a clinical environment. Finally, through calculation of the energy spectra and vorticity field, we observed ring-like vortices inside the cannula originating from the side holes, most prominent in the proximal position. Our work highlights the important differences between a patient-derived and simplified venous model, with the latter tending to underestimate tip drainage. We also draw attention to the different dynamics of single-stage and multistage drainage cannulas, which may guide clinical use. [ABSTRACT FROM AUTHOR]

Extracorporeal life support (ECLS) includes life-saving support in severe acute cardiac and/or pulmonary failure. In the past 20 years, centrifugal pumps have become the primary choice to deliver the required blood flow. Pumps of various designs, with different approved operating ranges, are today available to clinicians. The use of centrifugal pumps in the low flow condition has been shown to increase hemolytic and thrombogenic risks of the treatment. Further, low flow operation has been associated with retrograde flow at the pump inlet. In this study, experimental and numerical methods have been applied to investigate the operating conditions and fluid dynamical mechanisms leading to reverse flow (or backflow) at the inlet. Reverse flow was predominantly observed in pumps having a top shroud covering the impeller blades, showing a relation between pump geometry and backflow. The shroud divides the pump volume above the impeller into two regions, separating the swirling reverse flow migrating toward the upper pump volute from the main flow, reducing the dissipation of the vortical structures, and allowing the swirling reverse flow to reach further in the pump inlet. At the inlet, backflow was observed as stable recirculation areas at the side of the pump inlet. [ABSTRACT FROM AUTHOR]