Investigation of Risks for Cerebral Embolism Associated with the Hemodynamics of Cardiopulmonary Bypass Cannula: A Numerical Model

Cerebral emboli originating in the ascending aorta are a major cause of
noncardiac complications following cardiac surgery. The hemodynamics of
the aortic cannula has been proven to play a significant role in emboli
generation and distribution. The aim of the current study was to perform
a thorough numerical investigation in order to examine the effect of
the design and orientation of the cannula used during cardiopulmonary bypass
on the risk to develop cerebral embolism. Hemodynamic analyses compared
numerical models of 27 cases consisting of six different cannula
orientations, four aortic anatomies, and three cannula designs. The
cannula designs included a straight-tip (ST) cannula, a moderately
curved tip cannula (TIP1 ), and a sharp-angle curved cannula (TIP2 ).
Outcome measures included hemodynamic parameters such as emanating jet
velocity, jet velocity drop, maximal shear stress, aortic wall reaction,
emboli pathlines and distribution between upper and lower vessels, and
stagnation regions. Based on these parameters, the risks for hemolysis,
atheroembolism, and cerebral embolism were evaluated and compared. On
one hand, the jet emerging from the ST cannula generated large
wall-shear stress at the aortic wall; this may have triggered the
erosion and distribution of embolic atheromatous debris from the aortic
arch. On the other hand, it diverted more emboli from the clamp region
to the descending aorta and thus reduced the risk for cerebral embolism.
The TIP1 cannula demonstrated less shear stress on the aortic wall and
diverted more emboli from the clamp region toward the upper vessels. The
TIP2 cannula exhibited a stronger emanating jet, higher shear stress
inside the cannula, and highly disturbed flow, which was more stagnant
near the clamp region. Current findings support the significant impact
of the cannula design and orientation on emboli generation and
distribution. Specifically, the straight tip cannula demonstrated a
reduced risk of cerebral embolism, which may be pivotal in the clinical
setting.