The Hemodynamics of Small Arterial Return Cannulae for Venoarterial Extracorporeal Membrane Oxygenation

A computational and experimental study of veno-arterial extracorporeal membrane oxygenation in cardiogenic shock: defining the trade-off between perfusion and afterload

Veno-Arterial Extracorporeal Membrane Oxygenation (VA-ECMO) is a type of mechanical circulatory support used, among others, in case of cardiogenic shock, consisting in percutaneous cannulation of the femoral artery. Despite the widespread use of this procedure in clinical practice, a deeper understanding of the complex interaction between native and ECMO output, as well as the fluid dynamics and perfusion of aorta and its branches is still required. Herein, a numerical and experimental approach is presented to model a VA-ECMO procedure on a patient-specific aortic geometry. For both approaches, cardiogenic shock was modeled by considering three different severities of left ventricular failure (mild, moderate, and severe), corresponding to a reduction in cardiac output of 30%, 50%, and 70% relative to the healthy condition, respectively. For each case, different levels of the ECMO support were simulated, ranging from 0 to 6 l/min. The performance of the VA-ECMO configuration was evaluated in terms of both afterload increase and flow at all aortic branches. Both methods highlighted the afterload increase in high levels of ECMO support. Furthermore, numerical and experimental data revealed the existence of a trade-off level of ECMO support that guarantees healthy perfusion of all vessels with the lowest afterload. This correlation opened a pathway for the definition of a tool for determining a suitable level of ECMO support on the basis of the knowledge of patient-specific data.

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

BackgroundLarge 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.MethodsArterial 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.ResultsA 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.ConclusionSmaller 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.

Blood flow and emboli transport patterns during venoarterial extracorporeal membrane oxygenation: A computational fluid dynamics study

PROBLEM

Despite advances in Venoarterial Extracorporeal Membrane Oxygenation (VA-ECMO), a significant mortality rate persists due to complications. The non-physiological blood flow dynamics of VA-ECMO may lead to neurological complications and organ ischemia. Continuous retrograde high-flow oxygenated blood enters through a return cannula placed in the femoral artery which opposes the pulsatile deoxygenated blood ejected by the left ventricle (LV), which impacts upper body oxygenation and subsequent hyperoxemia. The complications underscore the critical need to comprehend the impact of VA-ECMO support level and return cannula size, as mortality remains a significant concern.

AIM

The aim of this study is to predict and provide insights into the complications associated with VA-ECMO using computational fluid dynamics (CFD) simulations. These complications will be assessed by characterising blood flow and emboli transport patterns through a comprehensive analysis of the influence of VA-ECMO support levels and arterial return cannula sizes.

METHODS

Patient-specific 3D aortic and major branch models, derived from a male patient's CT scan during VA-ECMO undergoing respiratory dysfunction, were analyzed using CFD. The investigation employed species transport and discrete particle tracking models to study ECMO blood (oxygenated) mixing with LV blood (deoxygenated) and to trace emboli transport patterns from potential sources (circuit, LV, and aorta wall). Two cannula sizes (15 Fr and 19 Fr) were tested alongside varying ECMO pump flow rates (50%, 70%, and 90% of the total cardiac output).

RESULTS

Cannula size did not significantly affect oxygen transport. At 90% VA-ECMO support, all arteries distal to the aortic arch achieved 100% oxygen saturation. As support level decreased, oxygen transport to the upper body also decreased to a minimum saturation of 73%. Emboli transport varied substantially between emboli origin and VAECMO support level, with the highest risk of cerebral emboli coming from the LV with a 15 Fr cannula at 90% support.

CONCLUSION

Arterial return cannula sizing minimally impacted blood oxygen distribution; however, it did influence the distribution of emboli released from the circuit and aortic wall. Notably, it was the support level alone that significantly affected the mixing zone of VA-ECMO and cardiac blood, subsequently influencing the risk of embolization of the cardiogenic source and oxygenation levels across various arterial branches.

Afterload pressure and left ventricular contractility synergistically affect left atrial pressure during veno-arterial ECMO

Background

Veno-arterial extra-corporeal membrane oxygenation (VA-ECMO) may cause adverse effects including increased left ventricular (LV) filling pressure, LV distension, and pulmonary edema. We aimed to quantify the effects of ECMO flow, LV contractility, aortic pressure (AoP), and ECMO configuration on left atrial pressure (LAP) during VA-ECMO for cardiogenic shock in a mock circulatory loop (MCL).

Methods

An MCL simulated a normal state, LV failure, right ventricular failure, and biventricular failure. The ECMO return cannula was placed in the femoral artery (retrograde flow) or ascending aorta (antegrade flow). ECMO flow was incrementally increased from 0 to 5 liter/min. LAP, mean AoP, ECMO flow, and total cardiac output were measured at steady state.

Results

During VA-ECMO, LAP increased linearly with AoP, with the slope greater in the presence of LV impairment compared to preserved LV function. When AoP was held constant, as is the goal of therapy in clinical management, ECMO flow had no effect on LAP. In multivariable linear regression, AoP and LV contractility (p < 0.001 for each) correlated independently with LAP, but ECMO flow did not. ECMO return flow direction had no effect on LAP.

Conclusions

AoP and LV contractility, but not circuit flow or direction, independently determine LAP under VA-ECMO support. By controlling each of these inputs, vasodilator and inotrope management may combine synergistically to prevent VA-ECMO-related complications.

Extracorporeal membrane oxygenation for cardiac arrest: what, when, why, and how

INTRODUCTION

Extracorporeal membrane oxygenation (ECMO) facilitated resuscitation was first described in the 1960s, but only recently garnered increased attention with large observational studies and randomized trials evaluating its use.

AREAS COVERED

In this comprehensive review of extracorporeal cardiopulmonary resuscitation (ECPR), we report the history of resuscitative ECMO, terminology, circuit configuration and cannulation considerations, complications, selection criteria, implementation and management, and important considerations for the provider. We review the relevant guidelines, different approaches to cannulation, postresuscitation management, and expected outcomes, including neurologic, cardiac, and hospital survival. Finally, we advocate for the participation in national/international Registries in order to facilitate continuous quality improvement and support scientific discovery in this evolving area.

EXPERT OPINION

ECPR is the most disruptive technology in cardiac arrest resuscitation since high-quality CPR itself. ECPR has demonstrated that it can provide up to 30% increased odds of survival for refractory cardiac arrest, in tightly restricted systems and for select patients. It is also clear, though, from recent trials that ECPR will not confer this high survival when implemented in less tightly protocoled settings and within lower volume environments. Over the next 10 years, ECPR research will explore the optimal initiation thresholds, best practices for implementation, and postresuscitation care.

The effect of arterial cannula tip position on differential hypoxemia during venoarterial extracorporeal membrane oxygenation

Interaction between native ventricular output and venoarterial extracorporeal membrane oxygenation (VA ECMO) flow may hinder oxygenated blood flow 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 flow to the upper extremities using computational fluid 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 flow 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 flow can be increased by advancing the arterial cannula tip towards the aortic arch.

Limb Ischemia Complications of Veno-Arterial Extracorporeal Membrane Oxygenation

Background

This study aimed to summarize and analyse the risk factors, clinical features, as well as prevention and treatment of limb ischemia complications in patients on veno-arterial extracorporeal membrane oxygenation (V-A ECMO).

Methods

We retrospectively analyzed 179 adult patients who had undergone V-A ECMO support in the Cardiac Care Unit of the First Hospital of Lanzhou University between March 2019 and December 2021. Patients were divided into the limb ischemia group (LI group) and the non-limb ischemia group (nLI group) according to whether limb ischemia occurred on the ipsilateral side of femoral artery cannulation. In the LI group, patients were salvaged with a distal perfusion cannula (DPC) according to each patient's clinical conditions. The baseline data and ECMO data were compared between the two groups, and risk factors for limb ischemia complications were screened using multiple logistic regression analysis.

Results

Overall, 19 patients (10.6%) had limb ischemia complications, of which 5 (2.8%) were improved after medication adjustment, 12 (8.4%) were salvaged with a DPC, and 2 had undergone surgical intervention. There were significant differences in terms of Extracorporeal Cardiopulmonary Resuscitation (ECPR), Intra-aortic balloon pump (IABP), peak vasoactive-inotropic score (VIS) within 24 h after ECMO (VIS-max), Left ventricular ejection fraction (LVEF), weaning from ECMO, and discharge rate between the two groups. ECPR, IABP, and VIS-max in the LI group were significantly higher than those in the nLI group, whereas weaning from ECMO, discharge rate, and LVEF were significantly lower in the LI group compared to those in the nLI group. Furthermore, multiple logistic regression analysis revealed that diabetes [odds ratio (OR) = 4.338, 95% confidence interval (CI): 1.193–15.772, P = 0.026], IABP (OR = 1.526, 95% CI: 1.038–22.026, P = 0.049) and VIS-max (OR = 1.054, 95% CI: 1.024–1.085, P < 0.001) were independent risk factors for limb ischemia complications in patients who underwent V-A ECMO.

Conclusion

Diabetes, prevalence of IABP and VIS-max value in analyzed groups were independent risk factors for predicting limb ischemia complications in patients who underwent V-A ECMO. The cannulation strategy should be optimized during the establishment of V-A ECMO, and limb ischemia should be systematically evaluated after ECMO establishment. A DPC can be used as a salvage intervention for the complications of critical limb ischemia.