Blood damage during cardiopulmonary bypass can trigger postoperative inflammatory responses and organ injury. Therefore, optimizing the blood circuit design to minimize damage remains essential. However, variations in venous drainage circuit configurations persist across facilities, and standardization remains limited.

Herein, we conducted computational fluid dynamics (CFD) analysis using the finite volume method to investigate the influence of venous drainage circuit shape on pressure loss, wall shear stress (WSS), and venous drainage flow. The circuit inner diameter (8–14 mm) and branching angle (20°–160°) varied, while the head pressure was set at −70 cmH₂O.

The venous drainage flow decreased as the branching angle increased, although not significantly. The pressure loss increased at higher flow rates, with a more pronounced effect when the inner diameter was reduced. Similarly, the WSS increased with both higher flow rates and smaller inner diameters, suggesting an elevated risk of blood damage. Multiple regression analysis identified venous drainage flow and circuit inner diameter as the primary determinants of WSS. Moreover, an inner diameter of 12 mm was determined to be optimal, as it effectively maintained venous drainage, while minimizing pressure loss and reducing the WSS.

Appropriate selection of circuit inner diameter is critical for mitigating the risk of blood damage, while ensuring the necessary venous drainage flow (∼7.0 L/min) for cardiopulmonary bypass in adults. These findings may facilitate the standardization and optimization of cardiopulmonary bypass circuit designs, thereby advancing safer cardiopulmonary support technologies.