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

Performance Comparison of Centered and Tilted Blunt and Lighthouse Tip Cannulae for Drainage in Extracorporeal Life Support

INTRODUCTION

Extracorporeal membrane oxygenation is a lifesaving treatment for patients with refractory acute respiratory, circulatory, or combined cardiopulmonary failure. The patient is cannulated with one or two cannulae for drainage and reinfusion of blood. Blood is drained from the patient, pumped through a membrane lung for oxygenation and returned to the patient. Treatment efficiency depends on correct cannula positioning and interactions between drainage and reinfusion cannula.

METHODS

An experimental setup was built to study the isolated drainage performance of 24 Fr rigid models of a blunt and lighthouse tip cannula, both when centered and when tilted towards the vessel wall. Planar particle image velocimetry was used to investigate the flow field with water as the fluid medium.

RESULTS

For similar flow configuration, higher shear stresses were recorded in the blunt tip rather than lighthouse tip cannula. Moreover, in the lighthouse tip cannula, side-holes furthest from the tip (proximal side-holes) had the highest drainage. Results did not change substantially when the cannula was tilted towards the vessel wall.

CONCLUSIONS

The effective drainage point of the lighthouse tip cannula was located near the proximal side-holes. Lower shear stresses were recorded in the lighthouse tip cannula when compared with the blunt tip cannula, for all considered flow rate ratios and cannula positions.

Development and Evaluation of a Novel Drainage Cannula for Venoarterial Extracorporeal Membrane Oxygenation

A critical factor in thrombus formation during venoarterial extracorporeal membrane oxygenation (VA ECMO) is prothrombotic flow dynamics generated by the drainage cannula's design. This study aimed to create and evaluate a novel drainage cannula design which optimized blood flow dynamics to reduce thrombus formation. Computational fluid dynamics (CFD) was used to iteratively vary drainage cannula design parameters such as inner wall shape and side hole shape. The final novel design was then placed in an ex vivo blood circulation loop, and compared against a Bio-Medicus cannula (n = 6, each). Clot volume, hemolysis, and other parameters were measured to assess thrombus formation markers. The novel design consisted of a parabolic inner wall profile with closely spaced side holes angled at 30º to align with flow. When tested in the ex vivo loop, the novel design resulted in lower instances (two vs . four) and volumes of clot in the cannula (360.5 ± 254.8 vs . 1258.0 ± 651.7 µl) when compared to the Bio-Medicus cannula. Results from tests assessing hemolysis, platelet activation, and other thrombotic markers revealed a noninferior relationship between the novel and Bio-Medicus designs. Future work will explore the clinical applicability of these findings.

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.

Flow characterization of Maquet and Bio-Medicus multi-stage drainage cannulae during venoarterial extracorporeal membrane oxygenation

BACKGROUND

Drainage cannulae extract blood from a patient during venoarterial extracorporeal membrane oxygenation (VA ECMO), a treatment that temporarily supports patients undergoing severe heart and/or lung dysfunction. Currently, the two most commonly used multi-stage drainage cannulae are manufactured by Maquet and Bio-Medicus, but their designs vary in many aspects which impacts the generated flow dynamics. Therefore, this study aimed to use computational fluid dynamics (CFD) to explore the flow characteristics of the aforementioned cannulae and their impact on complications such as thrombosis.

METHODS

The Maquet and Bio-Medicus cannulae were 3D modelled within a patient-specific geometry of the venous vasculature taken from a computed tomography scan of a patient undergoing VA ECMO. A drainage flow rate of 4 L/min was assigned to each cannula. Lastly, a stress blended eddy simulation turbulence model was employed to resolve bulk flow turbulence.

RESULTS

The proximal row of side holes in both cannulae generated high intensity counter-rotating vortices, thus generating supraphysiological shear. These proximal rows were also responsible for the majority of flow extraction in both cannulae (>1.6 L/min). Despite identical simulation settings, each cannulae had differing impacts on global flow dynamics. For instance, the Bio-Medicus model produced a total stagnant blood volume of 25.6 ml, compared to 17.8 ml the Maquet cannula, thereby increasing the risk of thrombosis.

CONCLUSIONS

Overall, our results demonstrate that differences in design clearly impact flow dynamics and risk of complications. Therefore, further work in optimizing cannula design may be beneficial to prevent harmful flow characteristics.

In silico parametric analysis of femoro-jugular venovenous ECMO and return cannula dynamics: In silico analysis of femoro-jugular VV ECMO

BACKGROUND

Increasingly, computational fluid dynamics (CFD) is helping explore the impact of variables like: cannula design/size/position/flow rate and patient physiology on venovenous (VV) extracorporeal membrane oxygenation (ECMO). Here we use a CFD model to determine what role cardiac output (CO) plays and to analyse return cannula dynamics.

METHODS

Using a patient-averaged model of the right atrium and venae cava, we virtually inserted a 19Fr return cannula and a 25Fr drainage cannula. Running large eddy simulations, we assessed cardiac output at: 3.5-6.5 L/min and ECMO flow rate at: 2-6 L/min. We analysed recirculation fraction (Rf), time-averaged wall shear stress (TAWSS), pressure, velocity, and turbulent kinetic energy (TKE) and extracorporeal flow fraction (EFF = ECMO flow rate/CO).

RESULTS

Increased ECMO flow rate and decreased CO (high EFF) led to increased Rf (R = 0.98, log fit). Negative pressures developed in the venae cavae at low CO and high ECMO flow (high CR). Mean return cannula TAWSS was >10 Pa for all ECMO flow rates, with majority of the flow exiting the tip (94.0-95.8 %).

CONCLUSIONS

Our results underpin the strong impact of CO on VV ECMO. A simple metric like EFF, once supported by clinical data, might help predict Rf for a patient at a given ECMO flow rate. The return cannula imparts high shear stresses on the blood, largely a result of the internal diameter.

The effect of drainage cannula tip position on risk of thrombosis during venoarterial extracorporeal membrane oxygenation

BACKGROUND AND OBJECTIVES

Venoarterial extracorporeal membrane oxygenation (VA ECMO) is able to support critically ill patients undergoing refractory cardiopulmonary failure. It relies on drainage cannulae to extract venous blood from the patient, but cannula features and tip position may impact flow dynamics and thrombosis risk. Therefore, this study aimed to investigate the effect of tip position of single-stage (SS) and multi-stage (MS) VA ECMO drainage cannulae on the risk of thrombosis.

METHODS

Computational fluid dynamics was used to model flow dynamics within patient-specific geometry of the venous vasculature. The tip of the SS and MS cannula was placed in the superior vena cava (SVC), SVC-Right atrium (RA) junction, mid-RA, inferior vena cava (IVC)-RA junction, and IVC. The risk of thrombosis was assessed by measuring several factors. Blood residence time was measured via an Eulerian approach through the use of a scalar source term. Regions of stagnant volume were recognised by identifying regions of low fluid velocity and shear rate. Rate of blood washout was calculated by patching the domain with a scalar value and measuring the rate of fluid displacement. Lastly, wall shear stress values were determined to provide a qualitative understanding of potential blood trauma.

RESULTS

Thrombosis risk varied substantially with position changes of the SS cannula, which was less evident with the MS cannula. The SS cannula showed reduced thrombosis risk arising from stagnant regions when placed in the SVC or SVC-RA junction, whereas an MS cannula was predicted to create stagnant regions during all tip positions. When positioned in the IVC-RA junction or IVC, the risk of thrombosis was higher in the SS cannula than in the MS cannula due to both high and low shear flow.

CONCLUSION

Tip position of the drainage cannula impacts cannula flow dynamics and, subsequently, the risk of thrombosis. The use of MS cannulae can reduce high shear-related thrombosis, but SS cannulae can eliminate stagnant regions when advanced into the SVC. Therefore, the choice of cannula design and tip position should be carefully considered during cannulation.