Numerical investigation of the effect of side-hole geometry on shear stress distribution and blood damage in drainage cannula during venovenous extracorporeal membrane oxygenation

Venovenous extracorporeal membrane oxygenation is a critical life support technique for patients with severe respiratory failure refractory to conventional therapy. Special attention should be paid to the design of drainage cannulas because, unlike return cannulas, they generally have multiple side holes to improve hydraulic performance during blood suction. However, insertion of the drainage cannula in the vein can generate adverse flow dynamics induced by non-physiological conditions, which may increase risk of blood damage. To improve the efficacy and safety of drainage cannulas, this study investigated the effects of four side-hole configurations (number, spacing, angle, and arrangement) on the jet-like flow characteristics, shear stress distribution, and blood damage potential, using a large eddy simulation turbulence model within an idealized vessel-cannula model. High shear stress at the edge of side holes may cause erythrocyte damage and platelet activation, while flow separation at the cannula tip and downstream of side holes could induce thrombosis. In particular, overlapping regions of low shear stress and high oscillatory shear index were revealed, which exhibited a negative correlation. Our results indicated that superior side-hole geometry included a moderate number (4 rows) and intermediate spacing (20 mm) with 45° inclination. Non-linear arrangement could be considered to improve flow and shear stress distributions, if necessary. In conclusion, this study demonstrated that the side-hole geometry significantly influenced shear stress distribution and blood trauma, thereby providing quantitative guidance and theoretical support for the optimal design of drainage cannulas.