Native Cardiac Output Research Articles

Mechanical ventilation during extracorporeal membrane oxygenation support - New trends and continuing challenges.

The impact of mechanical ventilation on the survival of patients supported with veno-venous extracorporeal membrane oxygenation (V-V ECMO) due to severe acute respiratory distress syndrome (ARDS) remains still a focus of research. Recent guidelines, randomized trials, and registry data underscore the importance of lung-protective ventilation during respiratory and cardiac support on ECMO. This approach includes decreasing mechanical power delivery by reducing tidal volume and driving pressure as much as possible, using low or very low respiratory rate, and a personalized approach to positive-end expiratory pressure (PEEP) setting. Notably, the use of ECMO in awake and spontaneously breathing patients is increasing, especially as a bridging strategy to lung transplantation. During respiratory support in V-V ECMO, native lung function is of highest importance and adjustments of blood flow on ECMO, or ventilator settings significantly impact the gas exchange. These interactions are more complex in veno-arterial (V-A) ECMO configuration and cardiac support. The fraction on delivered oxygen in the sweep gas and sweep gas flow rate, blood flow per minute, and oxygenator efficiency have an impact on gas exchange on device side. On the patient side, native cardiac output, native lung function, carbon dioxide production (VCO2), and oxygen consumption (VO2) play a role. Avoiding pulmonary oedema includes left ventricle (LV) distension monitoring and prevention, pulse pressure >10mm Hg and aortic valve opening assessment, higher PEEP adjustment, use of vasodilators, ECMO flow adjustment according to the ejection fraction, moderate use of inotropes, diuretics, or venting strategies as indicated and according to local expertise and resources. Understanding the physiological principles of gas exchange during cardiac support on femoro-femoral V-A ECMO configuration and the interactions with native gas exchange and haemodynamics are essential for the safe applications of these techniques in clinical practice. Proning during ECMO remains to be discussed until further data is available from prospective, randomized trials implementing individualized PEEP titration during proning.

Discussion of hemodynamic optimization strategies and the canonical understanding of hemodynamics during biventricular mechanical support in cardiogenic shock: does the flow balance make the difference?

BackgroundMechanical circulatory support (MCS) devices may stabilize patients with severe cardiogenic shock (CS) following myocardial infarction (MI). However, the canonical understanding of hemodynamics related to the determination of the native cardiac output (CO) does not explain or support the understanding of combined left and right MCS. To ensure the most optimal therapy control, the current principles of hemodynamic measurements during biventricular support should be re-evaluated.MethodsHere we report a protocol of hemodynamic optimization strategy during biventricular MCS (VA-ECMO and left ventricular Impella) in a case series of 10 consecutive patients with severe cardiogenic shock complicating myocardial infarction. During the protocol, the flow rates of both devices were switched in opposing directions (+ / − 0.7 l/min) for specified times. To address the limitations of existing hemodynamic measurement strategies during biventricular support, different measurement techniques (thermodilution, Fick principle, mixed venous oxygen saturation) were performed by pulmonary artery catheterization. Additionally, Doppler ultrasound was performed to determine the renal resistive index (RRI) as an indicator of renal perfusion.ResultsThe comparison between condition 1 (ECMO flow > Impella flow) and condition 2 (Impella flow > VA-ECMO flow) revealed significant changes in hemodynamics. In detail, compared to condition 1, condition 2 results in a significant increase in cardiac output (3.86 ± 1.11 vs. 5.44 ± 1.13 l/min, p = 0.005) and cardiac index (2.04 ± 0.64 vs. 2.85 ± 0.69, p = 0.013), and mixed venous oxygen saturation (56.44 ± 6.97% vs. 62.02 ± 5.64% p = 0.049), whereas systemic vascular resistance decreased from 1618 ± 337 to 1086 ± 306 s*cm−5 (p = 0.002). Similarly, RRI decreased in condition 2 (0.662 ± 0.05 vs. 0.578 ± 0.06, p = 0.003).ConclusionsTo monitor and optimize MCS in CS, PA catheterization for hemodynamic measurement is applicable. Higher Impella flow is superior to higher VA-ECMO flow resulting in a more profound increase in CO with subsequent improvement of organ perfusion.Graphical

The effect of intra-aortic balloon pumping on hemodynamics and left ventricular load in Impella-supported condition: A simulation study

Abstract Introduction Intra-aortic balloon pumping (IABP) is a commonly used percutaneous mechanical circulatory support device. Although IABP combined with Impella, a percutaneous left ventricular assist device, has shown positive outcomes in a few case reports of acute heart failure, its hemodynamic and left ventricular (LV) unloading effects remain unclear. Purpose We conducted a simulation study to clarify the clinical benefits of adding IABP to Impella-supported conditions. Methods We used SimulinkⓇ for cardiovascular simulation. The systemic and pulmonary circulation were modelled by using a 5-element resistance-capacitance network with four ventricles represented by time-varying elastance and unidirectional valves (Figure 1A). We compared total systemic flow, coronary perfusion pressure (CPP), and pressure-volume relationships (PV loop) in severe LV dysfunction (LV end-systolic elastance: 0.2 mmHg/mL) under three scenarios: IABP with a 40 mL balloon volume added to baseline, IABP added to Impella CP support at P2 (partial support) and P8 (total support) (Figure 1B). Results As shown in Figure 2A, IABP increased total systemic flow and CPP, and shifted the PV loop to the left. In P2-Impella condition, the addition of IABP increased native cardiac output (0.3 to 0.7 L/min) and total systemic flow (2.7 to 2.9 L/min), while decreased Impella pump flow due to increased afterload of Impella during diastole. IABP further moved PV loop leftward and reduced LV pressure-volume area (PVA) by -3.8% from Impella only and -7.8% from baseline (Figure 2B). In P8-Impella condition, IABP did not change total systemic flow, CPP, or PV loop (Figure 2C). Conclusions The addition of IABP to Impella could increase CPP while increasing Impella pump afterload and decreasing Impella flow. Overall, IABP slightly increased total systemic flow and decreased LV workload in Impella partial support condition. In specific clinical situations, IABP has the potential to be used as adjuvant therapy alongside Impella partial support.Figure 1

A large arteriovenous fistula steals a considerable part of systemic blood flow during veno-arterial extracorporeal circulation support in a porcine model.

Background: Veno-arterial extracorporeal membrane oxygenation (V-A ECMO) is one of the most frequently used mechanical circulatory support devices. Distribution of extracorporeal membrane oxygenation flow depends (similarly as the cardiac output distribution) on regional vascular resistance. Arteriovenous fistulas (AVFs), used frequently as hemodialysis access, represent a low-resistant circuit which steals part of the systemic perfusion. We tested the hypothesis that the presence of a large Arteriovenous fistulas significantly changes organ perfusion during a partial and a full Veno-arterial extracorporeal membrane oxygenation support. Methods: The protocol was performed on domestic female pigs held under general anesthesia. Cannulas for Veno-arterial extracorporeal membrane oxygenation were inserted into femoral artery and vein. The Arteriovenous fistulas was created using another two high-diameter extracorporeal membrane oxygenation cannulas inserted in the contralateral femoral artery and vein. Catheters, flow probes, flow wires and other sensors were placed for continuous monitoring of haemodynamics and organ perfusion. A stepwise increase in extracorporeal membrane oxygenation flow was considered under beating heart and ventricular fibrillation (VF) with closed and opened Arteriovenous fistulas. Results: Opening of a large Arteriovenous fistulas (blood flow ranging from 1.1 to 2.2L/min) resulted in decrease of effective systemic blood flow by 17%-30% (p < 0.01 for all steps). This led to a significant decrease of carotid artery flow (ranging from 13% to 25% after Arteriovenous fistulas opening) following VF and under partial extracorporeal membrane oxygenation support. Cerebral tissue oxygenation measured by near infrared spectroscopy also decreased significantly in all steps. These changes occurred even with maintained perfusion pressure. Changes in coronary artery flow were driven by changes in the native cardiac output. Conclusion: A large arteriovenous fistula can completely counteract Veno-arterial extracorporeal membrane oxygenation support unless maximal extracorporeal membrane oxygenation flow is applied. Cerebral blood flow and oxygenation are mainly compromised by the effect of the Arteriovenous fistulas. These effects could influence brain function in patients with Arteriovenous fistulas on Veno-arterial extracorporeal membrane oxygenation.

A case series evaluating the effect of esmolol therapy to treat hypoxemia in COVID-19 patients on VV-ECMO.

When COVID-19 ARDS abolishes pulmonary function, VV-ECMO can provide gas exchange. If oxygenation remains insufficient despite maximal VV-ECMO support, the addition of esmolol has been proposed. Conflict exists, however, as to the oxygenation level which should trigger beta-blocker initiation. We evaluated the effect of esmolol therapy on oxygenation and oxygen delivery in patients with negligible native lung function and various degrees of hypoxemia despite maximal VV-ECMO support. We found that, in COVID-19 patients with negligible pulmonary gas exchange, the generalized use of esmolol administration to raise arterial oxygenation by slowing heart rate and thereby match native cardiac output to maximal attainable VV ECMO flows actually reduces systemic oxygen delivery in many cases.

Modification of a Transvalvular Microaxial Flow Pump for Instantaneous Determination of Native Cardiac Output and Volume

The current Impella CP pump used for mechanical circulatory support (MCS) in patients with cardiogenic shock (CS) cannot assess native cardiac output (CO) and left ventricular (LV) volumes. This data is valuable in facilitating device management and weaning. Admittance technology allows for accurate assessment of cardiac chamber volumes. This study tested the ability to engineer admittance electrodes onto an existing Impella CP pump to assess total and native CO in an instantaneous manner, as well as LV chamber volumes. Impella CP pumps were fitted with four admittance electrodes and placed in the LV of adult swine (n=9) subjected to three different hemodynamic conditions including Impella CP speed adjustments, administration of escalating doses of dobutamine, and microsphere injections into the left main artery to result in cardiac injury. CO by admittance electrodes was calculated from LV volumes and heart rate. In addition, CO was calculated in each instance via thermodilution, continuous CO (CCO) measurement, Fick's principle and aortic velocity-time integral (VTI) by echocardiography. Modified Impella CP pumps were placed in swine LV successfully. CO as determined by admittance electrodes was similar by trend with other methods of CO assessment, corrected for pump speed to calculate native CO, and calculated LV chamber volumes trended as expected in each experimental protocol. We report for the first time that an Impella CP pump can be fitted with admittance electrodes and used to determine total and native CO in various hemodynamic situations. Transvalvular mechanical circulatory support (MCS) devices such as the Impella CP do not have the ability to provide real-time information on native cardiac output (CO) and left ventricular (LV) volumes. This information is critical in device management and weaning in patients with cardiogenic shock (CS). We demonstrate for the first time, an Impella CP pump coupled with admittance electrodes are able to determine native CO, and left ventricle (LV) chamber volumes in multiple different hemodynamic situations such as Impella pump speed adjustments, escalating dobutamine administration, and cardiac injury from microsphere injection.

Integral assessment of gas exchange during veno-arterial ECMO: accuracy and precision of a modified Fick principle in a porcine model.

Assessment of native cardiac output during extracorporeal circulation is challenging. We assessed a modified Fick principle under conditions such as dead space and shunt in 13 anesthetized swine undergoing centrally cannulated veno-arterial extracorporeal membrane oxygenation (V-A ECMO, 308 measurement periods) therapy. We assumed that the ratio of carbon dioxide elimination (V̇co2) or oxygen uptake (V̇o2) between the membrane and native lung corresponds to the ratio of respective blood flows. Unequal ventilation/perfusion (V̇/Q̇) ratios were corrected towards unity. Pulmonary blood flow was calculated and compared to an ultrasonic flow probe on the pulmonary artery with a bias of 99 mL/min (limits of agreement -542 to 741 mL/min) with blood content V̇o2 and no-shunt, no-dead space conditions, which showed good trending ability (least significant change from 82 to 129 mL). Shunt conditions led to underestimation of native pulmonary blood flow (bias -395, limits of agreement -1,290 to 500 mL/min). Bias and trending further depended on the gas (O2, CO2) and measurement approach (blood content vs. gas phase). Measurements in the gas phase increased the bias (253 [LoA -1,357 to 1,863 mL/min] for expired V̇o2 bias 482 [LoA -760 to 1,724 mL/min] for expired V̇co2) and could be improved by correction of V̇/Q̇ inequalities. Our results show that common assumptions of the Fick principle in two competing circulations give results with adequate accuracy and may offer a clinically applicable tool. Precision depends on specific conditions. This highlights the complexity of gas exchange in membrane lungs and may further deepen the understanding of V-A ECMO.

A two-circuit strategy for intraoperative extracorporeal support during single lung transplantation in a patient bridged with venovenous extracorporeal membrane oxygenation.

Venovenous extracorporeal membrane oxygenation is increasingly used as a bridging strategy in decompensating patients awaiting lung transplantation. Various approaches for continuing support intraoperatively have been previously described. A two-circuit strategy that uses the in situ venovenous extracorporeal membrane oxygenation circuit supplemented with peripheral cardiopulmonary bypass allows for diversion of native cardiac output away from the transplanted lung as well as seamless continuation of venovenous extracorporeal membrane oxygenation postoperatively.

Mechanical circulatory support in ventricular arrhythmias.

In atrial and ventricular tachyarrhythmias, reduced time for ventricular filling and loss of atrial contribution lead to a significant reduction in cardiac output, resulting in cardiogenic shock. This may also occur during catheter ablation in 11% of overall procedures and is associated with increased mortality. Managing cardiogenic shock and (supra) ventricular arrhythmias is particularly challenging. Inotropic support may exacerbate tachyarrhythmias or accelerate heart rate; antiarrhythmic drugs often come with negative inotropic effects, and electrical reconversions may risk worsening circulatory failure or even cardiac arrest. The drop in native cardiac output during an arrhythmic storm can be partly covered by the insertion of percutaneous mechanical circulatory support (MCS) devices guaranteeing end-organ perfusion. This provides physicians a time window of stability to investigate the underlying cause of arrhythmia and allow proper therapeutic interventions (e.g., percutaneous coronary intervention and catheter ablation). Temporary MCS can be used in the case of overt hemodynamic decompensation or as a “preemptive strategy” to avoid circulatory instability during interventional cardiology procedures in high-risk patients. Despite the increasing use of MCS in cardiogenic shock and during catheter ablation procedures, the recommendation level is still low, considering the lack of large observational studies and randomized clinical trials. Therefore, the evidence on the timing and the kinds of MCS devices has also scarcely been investigated. In the current review, we discuss the available evidence in the literature and gaps in knowledge on the use of MCS devices in the setting of ventricular arrhythmias and arrhythmic storms, including a specific focus on pathophysiology and related therapies.

Weaning from venous-arterial extracorporeal membrane oxygenation: The hemodynamic and clinical aspects of flow challenge test.

The cardiac function reserve is crucial for the successful weaning of V-A ECMO. During the V-A ECMO weaning phase, the gradual reduction in pump flow converts the blood flow originally driven by the pump to native cardiac output and also transforms afterload (caused by retrograde flow) into ventricular preload, thus introducing a “flow challenge” to the native heart. In this perspective, we propose to use this flow challenge as a test to simulate the preload-to-afterload conversion to assess cardiac functional reserve quantitatively. With this short article we offer the hemodynamic and clinical aspects regarding the flow challenge test.

Extracorporeal membrane oxygenation after prosthetic valve replacement in a child with neonatal Marfan syndrome: a case report

BackgroundNeonatal Marfan syndrome (nMFS), the most severe form of Marfan syndrome, is a rare condition that presents a clinical and treatment challenge. nMFS has high infant mortality related to progressive valvular dysfunction. Valve replacement in this setting improves long-term prognosis but carries high morbidity and mortality. Thus, sharing clinical experience in treating such patients is valuable.Case summaryA 2 year old with nMFS underwent tricuspid valve annuloplasty and prosthetic mitral valve replacement. Postoperative management was complicated by pulmonary hypertension, cardiogenic shock, and arrythmias. Venoarterial extracorporeal membrane oxygenation (VA-ECMO) helped overcome these challenges but posed a high risk for prosthetic valve thrombosis (PVT). Despite decompression of the left atrium (LA) with an LA vent, the left ventricle (LV) was distended because of aortic regurgitation and no native cardiac output. We lowered the ECMO flow under echocardiographic guidance; used inodilators and pacing to encourage transmitral flow and reduce LV afterload. The patient completed a successful 6-day ECMO run with good end-organ perfusion. At last follow up, she was 6 years old, enjoying school, home-ventilated through the tracheostomy, and mobilizing with walking aids/wheelchair.DiscussionValve replacement can improve life quality and expectancy for patients with nMFS. Lowering ECMO flow under echocardiography guidance till the aortic valve is seen to open; coupled with inodilators, pacing and adequate anticoagulation can be a safe way to deliver VA-ECMO for cardiogenic shock after prosthetic valve replacement. Further research is needed to show if this strategy prevents prosthetic valve thrombosis and provides sufficient haemodynamic support and myocardial rest.

Dynamic and Hybrid Extracorporeal Membrane Oxygenation Configurations Require Greater Involvement of Vascular Surgeons

The use of extracorporeal membrane oxygenation (ECMO) for adult patients with refractory cardiac, pulmonary, or cardiopulmonary shock has increased dramatically in the past decades. A substantial and understudied subset of these patients will require reconfiguration of their ECMO circuit. The indications for reconfiguration include escalation or de-escalation of arterial support for changes in native cardiac output, anatomic considerations for limb compromise or thrombus formation, and transition to long-term support involving ventricular-assist devices.

Metabolic and Hemodynamic Determinants of Exercise with the HeartMate 3 LVAD

<h3>Purpose</h3> Several studies have reported that peak oxygen consumption (pVO2) is diminished after continuous flow (CF) LVAD support and recent data shows that pVO2 post LVAD predicts outcomes. It has been suggested that augmentation of native cardiac output (NCO) and not LVAD flow supports exercise. Using simultaneous metabolic and hemodynamic measures, we further studied the determinants of maximal exercise with the Heartmate 3 (HM3) LVAD. <h3>Methods</h3> Subjects underwent maximal upright bicycle exercise testing utilizing a 10-15 W ramp protocol with hemodynamic measurements from a right heart and radial arterial catheter, and CPET testing with a metabolic cart (Metalyzer 3B, Cortex, Germany). Mid-point hemodynamics were acquired to plot pressure/flow relationships. NCO was calculated by subtracting LVAD flow from Fick cardiac output (FCO). Arterial lactate and regional tissue oxygenation (rSO2) with the NIRS SenSmart™ were also measured. <h3>Results</h3> Six HM3 subjects (43-76 yrs) were studied at least 12 weeks post implant, all were on at least 2 neurohormonal agents. All patients performed maximal exercise (RER 1.10-1.34). Most did not demonstrate chronotropic incompetence; achieving median 80.8 (63.5- 90.9) % of predicted heart rate. We saw robust oxygen extraction, with median peak A-VO2 difference 14.2 (10.5-15.8) mL/100mL with no change in rSO2 and median peak lactate 6.5 (3.5-9.9) mmol/L. However, 5/6 subjects achieved pVO2 ≤14 ml/kg/min. During exercise, there was minimal augmentation of LVAD flow (0.4-1.6 L/min) while NCO increased by 2.0-7.1 L/min. Mean pulmonary artery (mPA)/FCO relationships were available for 5 subjects (Fig.1), demonstrating abnormal rate of rise of mPA in all patients (slope 3.7-7.0, normal < 3). <h3>Conclusion</h3> Neither chronotropic response nor peripheral extraction appeared to limit exercise. Steep rise in mPA suggests either impaired pulmonary vasoreactivity and or cardiac reserve may be the key determinants of exercise capacity during HM3 support. Further study will clarify these factors.

CT Angiography of Venoarterial Extracorporeal Membrane Oxygenation.

Imaging plays a central role in the workup of thromboembolic events and bleeding complications in patients treated with venoarterial extracorporeal membrane oxygenation (ECMO) (VA-ECMO), and radiologists should be familiar with the expected hemodynamic changes and flow-related artifacts associated with the VA-ECMO system. VA-ECMO is a form of temporary mechanical circulatory support for critically ill patients with acute, refractory cardiac or cardiopulmonary failure. As the use of VA-ECMO continues to increase, it is important to be aware of associated hemodynamic changes and challenges at imaging. Patients treated with VA-ECMO are at high risk for thromboembolic events and bleeding complications and, thus, often require evaluation with CT angiography (CTA). VA-ECMO can be implemented by using central or peripheral cannulation. The peripheral femorofemoral VA-ECMO circuit in particular alters the sequence and direction of contrast medium enhancement substantially, resulting in flow-related artifacts that can mimic or obscure disease at CTA. Nonopacification can be mistaken for spurious thrombus or simulate complete vascular occlusion, while mixing artifacts can mimic dissections. Misinterpretation of flow-related CTA artifacts can lead to inappropriate surgical or medical intervention. A methodical and multiphasic approach should be taken to CTA imaging strategies and interpretation for patients treated with VA-ECMO. There is no universal CTA protocol for patients on VA-ECMO. Each protocol must be designed for the study indication, with consideration of the configuration of the ECMO cannulas, contrast material injection site, region of interest, native cardiac output, and ECMO flow rate. The authors provide examples of common and unusual VA-ECMO-related artifacts, with a focus on strategies for optimizing CTA image acquisition. Online supplemental material is available for this article. ©RSNA, 2021.

Hybrid and parallel extracorporeal membrane oxygenation circuits

Hybrid and parallel extracorporeal membrane oxygenation circuits

Concomitant Respiratory Failure Can Impair Myocardial Oxygenation in Patients with Acute Cardiogenic Shock Supported by VA-ECMO

Venous-arterial extracorporeal membrane oxygenation (VA-ECMO) treatment for acute cardiogenic shock in patients who also have acute lung injury predisposes development of a serious complication called “north-south syndrome” (NSS) which causes cerebral hypoxia. NSS is poorly characterized and hemodynamic studies have focused on cerebral perfusion ignoring the heart. We hypothesized in NSS the heart would be more likely to receive hypoxemic blood than the brain due to the proximity of the coronary arteries to the aortic annulus. To test this, we conducted a computational fluid dynamics simulation of blood flow in a human supported by VA-ECMO. Simulations quantified the fraction of blood at each aortic branching vessel originating from residual native cardiac output versus VA-ECMO. As residual cardiac function was increased, simulations demonstrated myocardial hypoxia would develop prior to cerebral hypoxia. These results illustrate the conditions where NSS will develop and the relative cardiac function that will lead to organ-specific hypoxia.Graphical Illustration of the impact of north-south syndrome on organ-specific oxygen delivery. Patients on VA-ECMO have two sources of blood flow, one from the VA-ECMO circuit and one from the residual cardiac function. When there is no residual cardiac function, all organs are perfused with oxygenated blood. As myocardial recovery progresses, blood supply from the two sources will begin to mix resulting in non-homogeneous mixing and differential oxygenation based upon the anatomical site of branching vessels.

Functional brain isolation technique for stroke prevention in thoracic endovascular aortic repair.

To prevent embolic stroke during thoracic endovascular aortic repair, we have adopted the brain isolation technique since June 2014 in 9 selected high-risk patients (9/134: 6.7%) having ulcerated or protruding atheromas within the proximal aorta. Cardiopulmonary bypass was used to prevent aortic atheromas from entering the brain. We used a heparin-coated closed-loop cardiopulmonary bypass system incorporating a soft reservoir bag with 1 mg/kg heparin to minimize the disadvantages of extracorporeal circulation. The bypass graft (right axillary-left carotid-left axillary) was used as an arterial inflow in patients undergoing zone-1 landing (n = 8), while peripheral cannulation into 3 brachiocephalic arteries was employed in the remaining patient. Initial pump flow was set at 1.3 l/min/m2, and native cardiac output was reduced by adjusting the reservoir bag volume. Aortography was performed to confirm non-visualization of the arch vessels before catheter manipulation. There was no mortality and 1 solitary left cerebellar infarction.

Hemodynamic adaptation of heart failure to percutaneous venoarterial extracorporeal circulatory supports.

Extracorporeal life support (ECLS) is a treatment modality that provides prolonged blood circulation, gas exchange and can partially support or fully substitute functions of heart and lungs in patients with severe but potentially reversible cardiopulmonary failure refractory to conventional therapy. Due to high-volume bypass, the extracorporeal flow is interacting with native cardiac output. The pathophysiology of circulation and ECLS support reveals significant effects on arterial pressure waveforms, cardiac hemodynamics, and myocardial perfusion. Moreover, it is still subject of research, whether increasing stroke work caused by the extracorporeal flow is accompanied by adequate myocardial oxygen supply. The left ventricular (LV) pressure-volume mechanics are reflecting perfusion and loading conditions and these changes are dependent on the degree of the extracorporeal blood flow. By increasing the afterload, artificial circulation puts higher demands on heart work with increasing myocardial oxygen consumption. Further, this can lead to LV distention, pulmonary edema, and progression of heart failure. Multiple methods of LV decompression (atrial septostomy, active venting, intra-aortic balloon pump, pulsatility of flow) have been suggested to relieve LV overload but the main risk factors still remain unclear. In this context, it has been recommended to keep the rate of circulatory support as low as possible. Also, utilization of detailed hemodynamic monitoring has been suggested in order to avoid possible harm from excessive extracorporeal flow.

Time-Resolved Echo-Particle Image/Tracking Velocimetry Measurement of Interactions Between Native Cardiac Output and Veno-Arterial ECMO Flows.

Determination of optimal hemodynamic and pressure-volume loading conditions for patients undergoing veno-arterial extracorporeal membrane oxygenation (VA-ECMO) would benefit from understanding the impact of ECMO flow rates (QE) on the native cardiac output in the admixing zone, i.e., aortic root. This study characterizes the flow in the aortic root of a pig with severe myocardial ischemia using contrast-enhanced ultrasound particle image/tracking velocimetry (echo-PIV/PTV). New methods for data preprocessing are introduced, including autocontouring to remove surrounding tissues, followed by blind deconvolution to identify the centers of elongated bubble traces in images with low signal to noise ratio. Calibrations based on synthetic images show that this procedure increases the number of detected bubbles and reduces the error in their locations by 50%. Then, an optimized echo-PIV/PTV procedure, which integrates image enhancement with velocity measurements, is used for characterizing the time-resolved two-dimensional (2D) velocity distributions. Phase-averaged and instantaneous flow fields show that the ECMO flow rate influences the velocity and acceleration of the cardiac output during systole, and secondary flows during diastole. When QE is 3.0 L/min or higher, the cardiac ejection velocity, phase interval with open aortic valve, velocity-time integral (VTI), and mean arterial pressure (MAP) increase with decreasing QE, all indicating sufficient support. For lower QE, the MAP and VTI decrease as QE is reduced, and the deceleration during transition to diastole becomes milder. Hence, for this specific case, the optimal ECMO flow rate is 3.0 L/min.

Pulse pressure and end-tidal carbon dioxide for monitoring low native cardiac output during veno-arterial ECLS: a prospective observational study

BackgroundVeno-arterial extracorporeal life support (VA-ECLS) results in cardiopulmonary shunting with reduced native cardiac output (NCO). Low NCO occurrence is common and associated with risk of thromboembolic and pulmonary complications. Practical tools for monitoring NCO during VA-ECLS would therefore be valuable. Pulse pressure (PP) and end-tidal carbon dioxide (EtCO2) are known to be related to cardiac output. We have designed a study to test whether PP and EtCO2 were efficient for the monitoring of NCO during VA-ECLS.MethodsIn this prospective single-center observational study, patients who underwent a VA-ECLS for cardiogenic shock from January 2016 to October 2017 were included, provided low NCO was suspected by a PP < 20 mmHg. NCO was measured with pulmonary artery catheter or echocardiography and compared to PP and EtCO2. The ability of PP and EtCO2 to predict NCO < 1 L/min was evaluated with receiver operating characteristics (ROC) curves.ResultsAmong the 106 patients treated with VA-ECLS for cardiogenic shock during the study period, 26 were studied, allowing the collection of 196 study points. PP and EtCO2 relationships with NCO were nonlinear and showed strong correlations for NCO < 2 L/min (r = 0.69 and r = 0.78 respectively). A PP < 15 mmHg and EtCO2 < 14 mmHg had good predictive values for detecting NCO < 1 L/min (area under ROC curve 0.93 [95% CI 0.89–0.96] and 0.97 [95% CI 0.94–0.99] respectively, p = 0.058).ConclusionsPP and EtCO2 may offer an accurate real-time monitoring of low NCO events during VA-ECLS support. Further studies are needed to show if their utilization may help to implement therapeutic strategies in order to prevent thromboembolic and respiratory complications associated with VA-ECLS, and to improve patients’ prognosis.Trial registrationNCT03323268, July 12, 2016