One or more holes? Comparative numerical analysis of bidirectional flow cannulas

The widespread use of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) in the last decade has encouraged the concept of various return cannulas aimed at ensuring bidirectional perfusion and avoiding limb ischemia. Yet, the local hemodynamics modification owing to bidirectional flow cannulas is poorly understood. Computational fluid dynamics simulations of two different bidirectional flow cannulas inserted within an idealized artery were performed. The cannula designs differ in elbow configuration. One design has a single hole (single-hole, SH cannula), while the other has four holes (multi-hole, MH cannula) at the elbow region. Simulations were run at two different perfusion flow rates, namely, 1.4 and 3.5 L/min, and compared with the hemodynamics of a standard one-directional cannula. Both cannulas achieved improved distal perfusion compared to the standard configuration, delivering between 14% and 23%, and 22.5% and 37% of the total ECMO flow through the SH and MH configurations, respectively. However, secondary circulations arose from the distal opening, resulting in a large stagnation region along the MH cannula body. Such a condition, which is recognized as a risk factor for thrombus formation, was less pronounced in the SH solution. The analysis shows that distal openings provide adequate limb perfusion, potentially reducing ischemia risk. The multi-opening solution results in more effective outcomes to some degree but may present stagnation if not properly sized, thus potentially compromising local hemodynamics.