Comparison of single-stage and multi-stage drainage cannula flow characteristics during venoarterial extracorporeal membrane oxygenation

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-omega 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.