Shaun D. Gregory

Venoarterial extracorporeal membrane oxygenation is a form of artificial heart–lung therapy able to support patients undergoing refractory cardio-respiratory failure. Drainage cannulae are responsible for extracting venous blood from the body via a negative pressure gradient induced by the pump downstream. However, the unique designs of single- and multi-stage cannulae, such as the presence of small inlets on the walls of the cannula (side holes), result in complex flow dynamics. This study evaluated flow features of both cannula designs using a stress blended eddy simulation turbulence model, within a patient-specific geometry of the venous system. The wall-adapted local eddy viscosity subgrid-scale model was used to resolve the large eddies directly in the free stream region, while small eddies were modeled using the k–ω shear stress transport model in the near-wall region. Flow within both cannulae was dominated by turbulent structures, such as counter-rotating vortex pairs, followed by a region of flow separation created by the entering jet. This phenomenon was synonymous with a jet in a crossflow, but involved multiple tandem and opposing jets in an internal tubular environment. The single-stage cannula drained 38% of the total flow via the most proximal holes compared to the multi-stage cannula (52.8%). The single-stage cannula allowed for larger tip velocities and was able to extract more flow from the upper body. Overall, this study demonstrated notable differences in blood flow dynamics between single- and multi-stage cannulae, which can be applied in clinical selection and cannula design.

Veno-venous extracorporeal membrane oxygenation (VV-ECMO) supports patients with severe respiratory failure not responding to conventional treatments. Single-site jugular venous cannulation with dual-lumen cannulas (DLC) have several advantages over traditional single-lumen cannulas, however, bleeding and thrombosis are common, limiting their clinical utility. This study numerically investigated the effects of DLC side holes on blood flow dynamics since the maximum wall shear stress (WSS) occurs around the side holes. A DLC based on the Avalon Elite 27Fr model was implanted into an idealized 3D model of the vena cava and right atrium (RA). Eight DLCs were developed by changing the number, diameter, and spacing of side holes through an iterative design process. Physiologic flow at the inferior vena cava (IVC) and superior vena cava (SVC) were applied along with a partial ECMO support of 2 L/min. The SST k-ω turbulent model was solved for 6.4 seconds. WSS, washout, stagnation volume, and recirculation were compared. For all DLCs, no stasis region lasted more than one cardiac cycle and a complete washout was obtained in less than 4 seconds. Due to the IVC and SVC backflows, maximum WSS occurred around the DLC side holes at late systole and late diastole. A DLC with 16 and three side holes within the IVC and SVC, respectively, reduced the maximum WSS by up to 67% over the Avalon Elite 27Fr. Improved DLCs provided a more uniform WSS distribution with lower WSS around the side holes, potentially reducing the chance of thrombosis and bleeding.