Aortic cannula orientation and flow impacts embolic trajectories: computational cardiopulmonary bypass

Abstract

Introduction: Emboli events are associated with the aortic cannula insertion and final position in the ascending aorta. However, the impact of subtle changes in aortic cannula movement and flow influencing embolic transport throughout the aortic arch is not well understood. The present study evaluated the aortic cannula’s outflow and orientation effect on emboli entering the aortic branch arteries. Methods: A simplified aortic computational model was anteriorly cannulated in the distal ascending aorta with a 21-French straight aortic cannula, and two orientations were analysed by injecting gaseous and solid emboli at pump flows 2, 3 and 5 L/minute. The first aortic cannula orientation (forward flow cannula) was directed towards the lesser curvature. The second aortic cannula orientation (rear flow cannula) was tilted slightly backwards by 15°, providing flow in the retrograde direction. Results: Forward flow cannula produced a primary arch flow, whereas rear flow cannula produced a secondary arch flow resulting in four times longer emboli arch resident times than forward flow cannula. The rear flow cannula had the highest percentage of gaseous emboli entering the brachiocephalic artery of 8%, 12% and 36% (at 2, 3 and 5 L/minute, respectively). Rear flow cannula provided a positive aortic branch arterial flow at all pump flows, whereas at forward flow cannula, the brachiocephalic artery experienced retrograde flows of −1.0% (3 L/minute) and −4.0% (5 L/minute), with the left common carotid −0.23% (5 L/minute). No significant number of solid emboli entered the aortic branch arteries. Conclusion: This numerical study illustrated distinct trajectory behaviours between gaseous and solid emboli where slight changes in aortic cannula orientation influenced idealised emboli direction with higher pump flows magnifying the effects.

Effect of aortic cannulation depth on air emboli transport during cardiopulmonary bypass: A computational study

“…This result demonstrated that the specific flow patterns are different for each cannula location and influenced by the two different cannula tip designs, thus illustrating how the AME pathlines followed the primary flow. 23 Therefore, the flow regime based on the cannula position could play a role in active AME management.…”

“…The 3D aorta model was discretised into a meshed domain with wall inflation layers based on earlier work. 23 The turbulent flow model ( k-ε ) and second-order pressure-flow coupling scheme were adopted for this simulation. The iteration calculations were terminated when the continuity, momentum and turbulence parameter residuals exceeded an order of (10 −5 ) and the mesh convergence had reached an asymptotic range of <5%.…”

“…22 In a previous study, the authors of this paper numerically investigated the cannula's orientation and flow rate, affecting the embolic load in the aortic arch's three main vessels. 23 The study demonstrated that flow rate and cannula orientation significantly impacted embolic load. However, typically, CFD simulations focus primarily on the 'sandblasting' effect, a cannula flow impingement that mobilises vulnerable atheromatous plaque.…”

A prospective observational study on the effect of emboli exposure on cerebral autoregulation in cardiac surgery requiring cardiopulmonary bypass

“…The brachiocephalic artery is the first and largest vessel arising from the aortic arch, and it is possible that the flow of blood from the tip of the arterial cannula (a potential source of some emobli) is directed toward this vessel. 20 A study of neurologic deficits after cardiac surgery reported predominant left sided hemiparesis. 21 If this asymmetry is attributed to the distribution of emboli, this could reflect the higher right sided embolic count.…”