The impact of small movements with dual lumen cannulae during venovenous extracorporeal membrane oxygenation: A computational fluid dynamics analysis.

BACKGROUND AND OBJECTIVES: Venovenous Extracorporeal Membrane Oxygenation (VV ECMO) provides respiratory support to patients with severe lung disease failing conventional medical therapy. An essential component of the ECMO circuit are the cannulas, which drain and return blood into the body. Despite being anchored to the patient to prevent accidental removal, minor cannula movements are common during ECMO. The clinical and haemodynamic consequences of these small movements are currently unclear. This study investigated the risk of thrombosis and recirculation caused by small movements of a dual lumen cannula (DLC) in an adult using computational fluid dynamics. METHODS: The 3D model of an AVALON Elite DLC (27 Fr) and a patient-specific vena cava and right atrium were generated for an adult patient on ECMO. The baseline cannula position was generated where the return jet enters the tricuspid valve. Alternative cannula positions were obtained by shifting the cannula 5 and 15 mm towards inferior (IVC) and superior (SVC) vena cava, respectively. ECMO settings of 4 L/min blood flow and pulsatile flow at SVC and IVC were applied. Recirculation was defined as a scalar value indicating the infused oxygenated blood inside the drainage lumen, while thrombosis risk was evaluated by shear stress, stagnation volume, washout, and turbulent kinetic energy. RESULTS: Recirculation for all models was less than 3.1 %. DLC movements between -5 to 15 mm increased shear stress and turbulence kinetic energy up to 24.7 % and 11.8 %, respectively, compared to the baseline cannula position leading to a higher predicted thrombosis risk. All models obtained a complete washout after nine seconds except for when the cannula migrated 15 mm into the SVC, indicating persisting stasis and circulating zones. CONCLUSION: In conclusion, small DLC movements were not associated with an increased risk of recirculation. However, they may increase the risk of thrombosis due to increased shear rate, turbulence, and slower washout of blood. Developing effective cannula securement devices may reduce this risk.

Computational analysis of thrombosis risk with variations in left ventricular assist device inflow cannula design in a multi-patient model.

BACKGROUND AND OBJECTIVES: Left ventricular assist devices (LVADs) are mechanical pumps used to support patients with end-stage heart failure. The inflow cannula is a critical component of the LVAD as it connects the pump to the left ventricle, allowing blood to be drawn from the heart. However, the design of the cannula can significantly impact LV hemodynamics and cause complications, including thrombosis. Therefore, this study aimed to analyze the numerical effects of left ventricle (LV) size on cannula design in order to enhance hemodynamic performance using post-operative left ventricular assist device (LVAD) models. METHODS: A parametric design evaluation of two different inflow cannulas were carried out on left ventricles (LV) of varying sizes (ranging from 154 to 430 ml) constructed from computerized tomography (CT) data from VAD patients using computational fluid dynamics (CFD) simulations. The study analyzed three key factors contributing to thrombosis formation: blood residence time, blood stagnation ratio, and wall shear stress. RESULTS: Results showed higher blood residence time and stagnation ratio for larger left ventricular sizes. In addition, increasing the insertion length of the cannula reduced the average wall shear stress. CONCLUSION: Overall, the study's findings suggest that the optimal cannula shape for LVADs varies with left ventricular size.

Improved Flow Dynamics of Extracorporeal Membrane Oxygenation via Design Modification of Dual-Lumen Cannulas.

Veno-venous extracorporeal membrane oxygenation (VV-ECMO) supports patients with severe respiratory failure not responding to conventional treatments. Single-site jugular venous cannulation with dual-lumen cannulas (DLC) have several advantages over traditional single-lumen cannulas, however, bleeding and thrombosis are common, limiting their clinical utility. This study numerically investigated the effects of DLC side holes on blood flow dynamics since the maximum wall shear stress (WSS) occurs around the side holes. A DLC based on the Avalon Elite 27Fr model was implanted into an idealized 3D model of the vena cava and right atrium (RA). Eight DLCs were developed by changing the number, diameter, and spacing of side holes through an iterative design process. Physiologic flow at the inferior vena cava (IVC) and superior vena cava (SVC) were applied along with a partial ECMO support of 2 L/min. The SST k-ω turbulent model was solved for 6.4 seconds. WSS, washout, stagnation volume, and recirculation were compared. For all DLCs, no stasis region lasted more than one cardiac cycle and a complete washout was obtained in less than 4 seconds. Due to the IVC and SVC backflows, maximum WSS occurred around the DLC side holes at late systole and late diastole. A DLC with 16 and three side holes within the IVC and SVC, respectively, reduced the maximum WSS by up to 67% over the Avalon Elite 27Fr. Improved DLCs provided a more uniform WSS distribution with lower WSS around the side holes, potentially reducing the chance of thrombosis and bleeding.

Improved Drainage Cannula Design to Reduce Thrombosis in Veno-Arterial Extracorporeal Membrane Oxygenation.

Thrombosis is a potentially life-threatening complication in veno-arterial extracorporeal membrane oxygenation (ECMO) circuits, which may originate from the drainage cannula due to unfavorable blood flow dynamics. This study aims to numerically investigate the effect of cannula design parameters on local fluid dynamics, and thus thrombosis potential, within ECMO drainage cannulas. A control cannula based on the geometry of a 17 Fr Medtronic drainage cannula concentrically placed in an idealized, rigid-walled geometry of the right atrium and superior and inferior vena cava was numerically modeled. Simulated flow dynamics in the control cannula were systematically compared with 10 unique cannula designs which incorporated changes to side hole diameter, the spacing between side holes, and side hole angles. Local blood velocities, maximum wall shear stress (WSS), and blood residence time were used to predict the risk of thrombosis. Numerical results were experimentally validated using particle image velocimetry. The control cannula exhibited low blood velocities (59 mm/s) at the cannula tip, which may promote thrombosis. Through a reduction in the side hole diameter (2 mm), the spacing between the side holes (3 mm) and alteration in the side hole angle (30° relative to the flow direction), WSS was reduced by 52%, and cannula tip blood velocity was increased by 560% compared to the control cannula. This study suggests that simple geometrical changes can significantly alter the risk of thrombosis in ECMO drainage cannulas.