Aortic Outflow Cannula Tip Design and Orientation Impacts Cerebral Perfusion during Pediatric Cardiopulmonary Bypass Procedures

Poor perfusion of the aortic arch is a suspected cause for peri- and post-operative neurological complications associated with cardiopulmonary bypass
(CPB). High-speed jets from 8 to 10FR pediatric/neonatal cannulae
delivering ~1 L/min of blood can accrue sub-lethal hemolytic damage
while also subjecting the aorta to non-physiologic flow conditions that
compromise cerebral perfusion. Therefore, we emphasize the importance of
cannulation strategy and hypothesize engineering better CPB perfusion
through a redesigned aortic cannula tip. This study employs
computational fluid dynamics to investigate novel diffuser-tipped aortic
cannulae for shape sensitivity to cerebral perfusion, in an in silico
cross-clamped aortic arch model modeled with fixed outflow resistances.
17 parametrically altered configurations of an 8FR end-hole and several
diffuser cone angled tips in combination with jet incidence angles
toward or away from the head-neck vessels were studied. Experimental
pressure-flow characterizations were also conducted on these cannula tip
designs. An 8FR end-hole aortic cannula delivering 1 L/min along the
transverse aortic arch was found to give rise to backflow from the
brachicephalic artery (BCA), irrespective of angular orientation, for
the chosen ascending aortic insertion location. Parametric alteration of
the cannula tip to include a diffuser cone angle (tested up to 7°)
eliminated BCA backflow for any tested angle of jet incidence.
Experiments revealed that a 1 cm long 10° diffuser cone tip demonstrated
the best pressure-flow performance improvement in contrast with either
an end-hole tip or diffuser cone angles greater than 10°. Performance
further improved when the diffuser was preceded by an expanded four-lobe
swirl inducer attachment-a novel component. In conclusion, aortic
cannula orientation is crucial in determining net head-neck perfusion
but precise angulations and insertion-depths are difficult to achieve
practically. Altering the cannula tip to include a diffuser cone angle
has been shown for the first time to have potential in ensuring a net
positive outflow at the BCA. Cannula insertion distanced from the BCA
inlet may also avoid backflow owing to the Venturi effect, but the
diffuser tipped cannula design presents a promising solution to mitigate
this issue irrespective of in vivo cannula tip orientation.