Development of a hemodynamically optimized outflow cannula for cardiopulmonary bypass.

The jet of the outflow cannula is a potential risk for patients undergoing cardiopulmonary bypass (CPB), because increased jet velocities lead to altered flow conditions and might furthermore mobilize atherosclerotic plaques from calcified aortas. The cannula jet is therefore among the main reasons for cerebral hypoxia and stroke in CPB patients. In the past, we developed a validated computational fluid dynamics (CFD) model to analyze flow conditions during CPB as dependent on cannulation and support modalities. This model is now applied to develop a novel CPB outflow cannula to reduce the jet effect and increase cerebral blood flow. The Multi-Module Cannula (MMC) is based on a generic elbow cannula that was iteratively improved. It features an inner wall to smoothly guide the blood as well as an elliptically shaped outlet diffuser. During standard CPB conditions of 5 L/min, the pressure drop over the MMC is 61 mm Hg, compared with 68 mm Hg with a standard cannula. The maximum velocities are decreased from 3.7 m/s to 3.3 m/s. In the cannula jet of the MMC, the velocities are reduced further, down to 1.6 m/s. The cerebral blood flow is typically reduced during CPB. Using the MMC, however, it reaches almost physiological values at 715 mL/min. These results suggest that the MMC outperforms standard CPB cannulas. Further design improvements and improved insertion techniques are under consideration.