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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 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. [ABSTRACT FROM AUTHOR]

Background: 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. A detailed knowledge of the fluid dynamics of the components under different scenarios is thus paramount to assess the thrombogenicity of the circuit. Methods: An investigation of the flow structures developing in a conventional lighthouse tip (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. Results: The results showed that the 90° bends of the flow through the side holes created a recirculation zone inside the cannula which increased residence time. Flow structures resembling a jet in a crossflow were also observed. The use of different hematocrits did not significantly affect drainage performances. The most proximal set of holes drained 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. In the drainage zone the non‐Newtonian behavior of blood was less relevant. Conclusions: The most proximal holes drained the largest amount of fluid. The flow features and distribution of flow rates among the holes showed little dependence on the hematocrit. The non‐Newtonian behavior of blood had a small influence on the dynamics of the flow. [ABSTRACT FROM AUTHOR]

The use of extracorporeal life support devices such as extracorporeal membrane oxygenation in adults requires cannulation of the patient's vessels with comparatively large diameter cannulae to allow circulation of large volumes of blood (>5 L/min). The cannula diameter and length are the major determinants for extracorporeal membrane oxygenation flow. Manufacturing companies present pressure-flow charts for the cannulae; however, these tests are performed with water. Aims of this study were 1. to investigate the specified pressure-flow charts obtained when using human blood as the circulating medium and 2. to support extracorporeal membrane oxygenation providers with pressure-flow data for correct choice of the cannula to reach an optimal flow with optimal hydrodynamic performance. Eighteen extracorporeal membrane oxygenation drainage cannulae, donated by the manufacturers (n = 6), were studied in a centrifugal pump driven mock loop. Pressure-flow properties and cannula features were described. The results showed that when blood with a hematocrit of 27% was used, the drainage pressure was consistently higher for a given flow (range 10%-350%) than when water was used (data from each respective manufacturer's product information). It is concluded that the information provided by manufacturers in line with regulatory guidelines does not correspond to clinical performance and therefore may not provide the best guidance for clinicians. [ABSTRACT FROM AUTHOR]

• Lower cardiac output increases recirculation in VV ECMO. • The ratio of cardiac output to ECMO flow rate is strongly correlated with recirculation fraction. • VV ECMO return cannulas expose blood to high shear stress (>10 Pa) at any ECMO flow rate. : Increasingly, computational fluid dynamics (CFD) is helping explore the impact of variables like: cannula design/size/position/flow rate and patient physiology on venovenous (VV) extracorporeal membrane oxygenation (ECMO). Here we use a CFD model to determine what role cardiac output (CO) plays and to analyse return cannula dynamics. : Using a patient-averaged model of the right atrium and venae cava, we virtually inserted a 19Fr return cannula and a 25Fr drainage cannula. Running large eddy simulations, we assessed cardiac output at: 3.5–6.5 L/min and ECMO flow rate at: 2–6 L/min. We analysed recirculation fraction (R f), time-averaged wall shear stress (TAWSS), pressure, velocity, and turbulent kinetic energy (TKE) and extracorporeal flow fraction (EFF = ECMO flow rate/CO). : Increased ECMO flow rate and decreased CO (high EFF) led to increased R f (R = 0.98, log fit). Negative pressures developed in the venae cavae at low CO and high ECMO flow (high CR). Mean return cannula TAWSS was >10 Pa for all ECMO flow rates, with majority of the flow exiting the tip (94.0–95.8 %). : Our results underpin the strong impact of CO on VV ECMO. A simple metric like EFF, once supported by clinical data, might help predict R f for a patient at a given ECMO flow rate. The return cannula imparts high shear stresses on the blood, largely a result of the internal diameter. [ABSTRACT FROM AUTHOR]