Flow capabilities of arterial and drainage cannulae during venoarterial extracorporeal membrane oxygenation: A simulation model.

BACKGROUND: Large cannulae can increase cannula-related complications during venoarterial extracorporeal membrane oxygenation (VA ECMO). Conversely, the ability for small cannulae to provide adequate support is poorly understood. Therefore, we aimed to evaluate a range of cannula sizes and VA ECMO flow rates in a simulated patient under various disease states. METHODS: Arterial cannulae sizes between 13 and 21 Fr and drainage cannula sizes between 21 and 25 Fr were tested in a VA ECMO circuit connected to a mock circulation loop simulating a patient with severe left ventricular failure. Systemic and pulmonary hypertension, physiologically normal, and hypotension were simulated by varying systemic and pulmonary vascular resistances (SVR and PVR, respectively). All cannula combinations were evaluated against all combinations of SVR, PVR, and VA ECMO flow rates. RESULTS: A 15 Fr arterial cannula combined with a 21 Fr drainage cannula could provide >4 L/min of total flow and a mean arterial pressure of 81.1 mmHg. Changes in SVR produced marked changes to all measured parameters, while changes to PVR had minimal effect. Larger drainage cannulae only increased maximum circuit flow rates when combined with larger arterial cannulae. CONCLUSION: Smaller cannulae and lower flow rates could sufficiently support the simulated patient under various disease states. We found arterial cannula size and SVR to be key factors in determining the flow-delivering capabilities for any given VA ECMO circuit. Overall, our results challenge the notion that larger cannulae and high flows must be used to achieve adequate ECMO support.

Axillary vein as an alternative venous access site for VV-ECMO cannulation: a case report.

BACKGROUND: Ultrasound-guided percutaneous axillary vein cannulation can reduce cannulation failure and mechanical complications, is as safe and effective as internal jugular vein cannulation, and is superior to subclavian vein cannulation using landmark technique. As far, reports of venovenous extracorporeal membrane oxygenation (VV-ECMO) with percutaneous axillary vein cannulation are rare. CASE PRESENTATION: A 64-year-old man presenting with dyspnea and chest tightness after aspirating sewage was admitted to the emergency department. Computed tomography (CT) showed diffuse exudation of both lungs and arterial blood gas analysis showed an oxygenation index of 86. He was diagnosed with aspiration pneumonia-induced acute respiratory distress syndrome (ARDS) and intubated for deteriorated oxygenation. Despite the combination therapy of protective mechanical ventilation and prone position, the patient's oxygenation deteriorated further, accompanied with multiple organ dysfunction syndrome, which indicated the requirement of support with VV-ECMO. However, vascular ultrasound detected multiple thrombus within bilateral internal jugular veins. As an alternative, right axillary vein was chosen as the access site of return cannula. Subsequently, femoral-axillary VV-ECMO was successfully implemented under the ultrasound guidance, and the patient's oxygenation was significantly improved. Unfortunately, the patient died of hyperkalemia-induced ventricular fibrillation after 36 h of VV-ECMO running. Despite the poor prognosis, the blood flow during ECMO run was stable, and we observed no bleeding complication, vascular injury, or venous return disorder. CONCLUSIONS: Axillary vein is a feasible alternative access site of return cannula for VV-ECMO if internal jugular vein access were unavailable.

Effect of flow rate ratio and positioning on a lighthouse tip ECMO return cannula.

Extracorporeal membrane oxygenation is a life-saving support therapy in the case of cardiopulmonary refractory failure. Its use is associated to complications due to the presence of artificial surfaces and supraphysiological stress conditions. Thus, knowledge of the fluid structures associated to each component can give insight into sources of blood damage. In this study, an experimentally validated numerical study of a conventional lighthouse tip cannula in return configuration was carried out to characterize the flow structures using water or a Newtonian blood analog with different flow rate ratios and cannula positioning and their influence on hemolysis. The results showed that strong shear layers developed where the jets from the side holes met the co-flow. Stationary backflow regions at the vessel wall were also present downstream of the cannula. In the tilted case, the recirculation was much more pronounced on the wide side and almost absent on the narrow side. Small vortical backflow structures developed at the side holes which behaved like obstacles to the co-flow, creating pairs of counter-rotating vortices, which induced locally higher risk of hemolysis. However, global hemolysis index did not show significant deviations. Across the examined flow rate ratios, the holes on the narrow side consistently reinfused a larger fraction of fluid. A radial force developed in the tilted case in a direction so as to recenter the cannula in the vessel.

Hemodynamics of small arterial return cannulae for venoarterial extracorporeal membrane oxygenation.

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.

Flow Dynamics and Mixing in Extracorporeal Support: A Study of the Return Cannula.

Cannulation strategies in medical treatment such as in extracorporeal life support along with the associated cannula position, orientation and design, affects the mixing and the mechanical shear stress appearing in the flow field. This in turn influences platelet activation state and blood cell destruction. In this study, a co-flowing confined jet similar to a return cannula flow configuration found in extracorporeal membrane oxygenation was investigated experimentally. Cannula diameters, flow rate ratios between the jet and the co-flow and cannula position were studied using Particle Image Velocimetry and Planar Laser Induced Fluorescence. The jet was turbulent for all but two cases, in which a transitional regime was observed. The mixing, governed by flow entrainment, shear layer induced vortices and a backflow along the vessel wall, was found to require 9-12 cannula diameters to reach a fully homogeneous mixture. This can be compared to the 22-30 cannula diameters needed to obtain a fully developed flow. Although not significantly affecting mixing characteristics, cannula position altered the development of the flow structures, and hence the shear stress characteristics.