Background: Venoarterial extracorporeal membrane oxygenation (ECMO) provides mechanical support for critically ill patients with cardiogenic shock.Typically, the size of the arterial return cannula is chosen to maximize flow.However, smaller arterial cannulae may reduce cannula-related complications and be easier to insert. This in vitro study quantified the hemodynamic effect of different arterial return cannula sizes in a simulated acute heart failure patient.Methods: Baseline support levels were simulated with a 17 Fr arterial cannula in an ECMO circuit attached to a cardiovascular simulator with targeted partial (2.0 L/ min ECMO flow, 60-65 mm Hg mean aortic pressure-MAP) and targeted full ECMO support (3.5 L/min ECMO flow and 70-75 mm Hg MAP). Return cannula size was varied (13-21 Fr), and hemodynamics were recorded while keeping ECMO pump speed constant and adjusting pump speed to restore desired support levels.Results: Minimal differences in hemodynamics were found between cannula sizes in partial support mode. A maximum pump speed change of +600 rpm was required to reach the support target, and arterial cannula inlet pressure varied from 79 (21 Fr) to 224 mm Hg (13 Fr). The 15 Fr arterial cannula could provide the target full ECMO support at the targeted hemodynamics; however, the 13 Fr cannula could not due to the high resistance associated with the small diameter. Conclusions:A 15 Fr arterial return cannula provided targeted partial and full ECMO support to a simulated acute heart failure patient. Balancing reduced cannula size and ECMO support level may improve patient outcomes by reducing cannula-related adverse events.

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Venoarterial extracorporeal membrane oxygenation is a form of artificial heart- lung therapy able to support patients undergoing refractory cardio-respiratory failure. Drainage cannulae are responsible for extracting venous blood from the body via a negative pressure gradient induced by the pump downstream. How- ever, the unique designs of single and multi-stage cannulae, such as the presence of small inlets on the walls of the cannula (side holes), result in complex flow dynamics. This study evaluated the flow features of both cannula designs using a stress blended eddy simulation turbulence model, within a patient-specific ge- ometry of the venous system. The wall-adapted local eddy viscosity subgrid-scale model was used to resolve the large eddies directly in the free stream region, while small eddies were modelled using the k-ω shear stress transport model in the near-wall region. Flow within both cannulae was dominated by turbulent structures such as counter rotating vortex pairs, followed by a region of flow sep- aration created by the entering jet. This phenomenon was synonymous with a jet in a crossflow, but involved multiple tandem and opposing jets in an inter- nal tubular environment. The single-stage cannula drained 38% of total flow via the most proximal holes compared to the multistage cannula (52.8%). The single-stage cannula allowed for larger tip velocities and was able to extract more flow from the upper body. Overall, this study demonstrated notable differences in blood flow dynamics between single and multi-stage cannulae, which can be applied in clinical selection and cannula design.

Interaction between native ventricular output and venoarterial extracorporeal membrane oxygenation (VA ECMO) ow may hinder oxygenated blood ow to the aortic arch branches, resulting in differential hypoxemia. Typically, the arterial cannula tip is placed in the iliac artery or abdominal aorta. However, the hemodynamics of a more proximal arterial cannula tip have not been studied before. This study investigated the effect of arterial cannula tip position on VA ECMO blood ow to the upper extremities using computational uid dynamics simulations. Four arterial cannula tip positions (P1. common iliac, P2. abdominal aorta, P3. descending aorta and P4. aortic arch) were compared with different degrees of cardiac dysfunction and VA ECMO support (50%, 80% and 90% support). P4 was able to supply oxygenated blood to the arch vessels at all support levels, while P1 to P3 only supplied the arch vessels during the highest level (90%) of VA ECMO support. Even during the highest level of support, P1 to P3 could only provide oxygenated VA-ECMO ow at 0.11 L/min to the brachiocephalic artery, compared with 0.5 L/min at P4. This study suggests that cerebral perfusion of VA ECMO ow can be increased by advancing the arterial cannula tip towards the aortic arch.