Limb ischemia prevention: an open problem explored by computational fluid dynamics

Limb ischemia has a high incidence (10-30%) in patients supported by peripheral Veno-Arterial Extracorporeal Membrane Oxygenation (VA-ECMO), negatively impacting long-term functional outcomes and survival. In recent years, bidirectional flow cannulae have shown promise as a solution to ensure distal limb perfusion, potentially eliminating the need for additional interventions. However, concerns remain about their local effects on haemodynamics close to the cannula insertion. We compared by numerical simulation the flow field in an idealised artery-cannula district considering three designs of cannula. All configurations are based on a standard cannula of 21Fr with three different geometries of the elbow. Cannula A has the one-directional standard configuration, while Cannula B and C include one and four secondary holes, respectively, as indicated in two published patents. To evaluate the efficacy of the new cannulae, we applied the same operative conditions. Specifically, a pressure of 0mmHg is applied at the distal and proximal extremities of the artery, and a flow condition of 1.4L/min is applied at the cannula inlet. The results show that Cannula B and C increase the distal limb perfusion. The secondary holes provide a flow of 0.32L/min and 0.56L/min, respectively. Furthermore, the numerical simulations evidence potential risks related to shear stress distribution in design A and C, displaying extended regions with low wall shear stress, WSS<0.4Pa. This condition favours clot formation and abnormal response of the wall. The presented numerical simulations partially confirm the efficacy of new return cannula as an alternative to the standard techniques.