Preclinical Studies on Pulsatile Veno-Arterial Extracorporeal Membrane Oxygenation: A Systematic Review

Comparison of Hemodynamic Circulation in Pulsatile and Nonpulsatile Extracorporeal Membrane Oxygenation Systems Using an In-Vitro Heart Model

This study conducts an in-vitro experiment using a mock circulation system that mimics human circulation to assess the veno-arterial extracorporeal membrane oxygenation (ECMO) system. This study aims to compare the hemodynamic effects of centrifugal and pulsatile ECMO systems on the body using an in-vitro cardiogenic shock model. The heart model used in this study involves a contracting blood sac with inlet and outlet valves, capable of maintaining arterial pressure between 80 and 120 mm Hg while delivering a blood flow of 1.8-2 L/min, effectively replicating a cardiogenic shock model. The contraction force in the heart model was generated using a pneumatic cylinder and gradually decreased to simulate reduced cardiac function. The initial blood flow rates of both ECMO systems were maintained at 2 L/min under identical conditions for a fair comparison. Upon reducing the stroke volume of the heart to 35 ml, the ECMO system with counter-pulsation control increased the cardiac output by 10.7% and systemic circulation by 3.8% compared with the conventional ECMO system. This study demonstrates the hemodynamic benefits provided by the sustained counter-pulsation in an in-vitro weakened heart model. Pulsatile flow ECMO systems may serve as an alternative to address the limitations of continuous flow ECMO systems.

In Silico Analysis of Pulsatile Flow Veno-Arterial Extracorporeal Membrane Oxygenation on Human Aorta Model

Electrocardiogram (ECG)-synchronized pulsatile veno-arterial extracorporeal membrane oxygenation (V-A ECMO) is a recent development in extracorporeal therapy for patients with severe cardiogenic shock. Although preclinical studies have shown benefits of pulsatile flow relative to continuous ECMO flow, none have explored the effects of the timing of ECMO pulses with respect to the cardiac cycle and its possible implications on ECMO complications. This study aimed to develop a computational fluid dynamics (CFD) model of V-A ECMO in a patient-specific human aorta and evaluate the effect of ECMO timing on cardiac unloading, surplus hemodynamic energy delivery, and mixing zone position. Using direct flow measurements from cardiogenic shock patients and an ECMO device, the model revealed that maximal left ventricular (LV) unloading occurred when the ECMO pulse was in early diastole (35-40% from LV peak systolic flow). Maximum surplus hemodynamic energy transmission to aortic branches occurred at 20% from LV peak systolic flow. This indicates a trade-off between heart afterload and hemodynamic energy delivery in selecting ECMO pulse timing. The mixing zone was primarily located in the aortic arch across timing configurations. Therefore, selecting ECMO pulse timing is crucial to maximizing the benefits of pulsatile flow in V-A ECMO treatment.

Evaluation of extra-corporeal membrane oxygenator cannulae in pulsatile and non-pulsatile pediatric mock circuits

BACKGROUND

This study evaluated the hemodynamic performance of arterial and venous cannulae in a compliant pediatric extracorporeal membrane oxygenation (ECMO) mock circuit in pulsatile and non-pulsatile flow conditions.

METHODS

The ECMO setup consisted of an oxygenator, diagonal pump, and standardized-length arterial/venous tubing with pressure transducers. A validated left-heart mock loop was adapted to simulate pediatric conditions. The pulsatile flow was driven by a computer-controlled piston pump set at 120 bpm. A roller pump was used for non-pulsatile conditions. The circuit was primed with 40% glycerol-based solution. The cardiac output was set to 1 L/min and the aortic pressure to 40-50 mmHg. Four arterial cannulae (8Fr, 10Fr, 12Fr, 14Fr) and five venous cannulae (12Fr, 14Fr, 16Fr, 18Fr, 20Fr) (Medtronic, Inc., Minneapolis, MN, USA) were tested at increasing flow rate in 12 combinations.

RESULTS

The pulsatile condition required lower ECMO pump speeds for all cannulae combinations at a given flow rate, inducing a significantly smaller increase of flow in the mock loop. Under non-pulsatile conditions, the aortic and arterial pressures in the cannulae were higher (p < 0.01) while no significant differences in pressure drop and pressure-flow characteristics (M-number) were observed. The total hemodynamic energy was higher in case of non-pulsatile flow (p < 0.01).

CONCLUSION

Under non-pulsatile conditions, the system was characterized by overall higher pressures, resulting in higher support to the patient. The consequent increase of potential energy compensates for increases of kinetic energy, leading to a higher total hemodynamic energy. Pressure gradients and M number are independent of the testing conditions. Pulsatile testing conditions led to more physiological testing conditions, and it is recommended for ECMO testing.

Effect of chest compressions in addition to extracorporeal life support on carotid flow in an experimental model of refractory cardiac arrest in pigs

Background

Extracorporeal life support (ECLS) provides organ perfusion in refractory cardiac arrest but during the initiation of ECLS mean arterial pressure (MAP) and carotid flow may be suboptimal due to hypotension and/or insufficient flow. We hypothesized that cardiopulmonary resuscitation (CPR) in addition to ECLS may increase carotid flow and MAP compared to ECLS alone.

Methods

Observational pilot study comparing hemodynamic parameters before and after CPR cessation in pigs supported by ECLS for experimental refractory cardiac arrest. Pigs were anesthetized, ventricular fibrillation was induced for 3 min, automated CPR performed for 30 min, ECLS was initiated then CPR stopped.Variables averaged over 3 s were compared between the last 3 s of CPR + ECLS and 3, 6, 30 s, and 5 and 10 min of ECLS alone. Data are expressed as medians (25-75 interquartile range) and compared using paired samples Wilcoxon test.

Results

Nine pigs were included, ECLS was initiated at 2.7 (2.3-2.8) L/min. MAP during CPR + ECLS was 56(53.0-59.2) mmHg, versus 50(45-57)mmHg, 52(46-59)mmHg, 61(50-63)mmHg, 57 (54-66)mmHg, 54 (47-58)mmHg of ECLS alone, p = 0.50, 0.61, 0.70, 0.44, 0.73 respectively. Carotid flow was 113(78-119) ml/min during CPR + ECLS versus 99(79-110)ml/min, 100(81-110)ml/min, 96(60-122)ml/min, 118 (101-130)ml/min, 124 (110-141)ml/min, p = 0.41, 0.52, 0.73, 0.33, 0.20 respectively. When ECLS was initiated at lower flow, 1.5 L/min (one pig), MAP decreased from 59 to 45 mmHg, and carotid flow from 78.2 to 32.5 ml/min after 3 s of ECLS alone.

Conclusion

Stopping CPR after effective ECLS initiation does not decrease MAP or carotid flow. Future studies may evaluate augmenting low flow ECLS with CPR.

Exploring the Impact of Extracorporeal Membrane Oxygenation on the Endothelium: A Systematic Review

Extracorporeal membrane oxygenation (ECMO) is a life-saving intervention for patients with circulatory and/or pulmonary failure; however, the rate of complications remains high. ECMO induces systemic inflammation, which may activate and damage the endothelium, thereby causing edema and organ dysfunction. Advancing our understanding in this area is crucial for improving patient outcomes during ECMO. The goal of this review is to summarize the current evidence of the effects of ECMO on endothelial activation and damage in both animals and patients. PubMed and Embase databases were systematically searched for both clinical and animal studies including ECMO support. The outcome parameters were markers of endothelial activation and damage or (in)direct measurements of endothelial permeability, fluid leakage and edema. In total, 26 studies (patient n = 16, animal n = 10) fulfilled all eligibility criteria, and used VA-ECMO (n = 13) or VV-ECMO (n = 6), or remained undefined (n = 7). The most frequently studied endothelial activation markers were adhesion molecules (ICAM-1) and selectins (E- and P-selectin). The levels of endothelial activation markers were comparable to or higher than in healthy controls. Compared to pre-ECMO or non-ECMO, the majority of studies showed stable or decreased levels. Angiopoietin-2, von Willebrand Factor and extracellular vesicles were the most widely studied circulating markers of endothelial damage. More than half of the included studies showed increased levels when compared to normal ranges, and pre-ECMO or non-ECMO values. In healthy animals, ECMO itself leads to vascular leakage and edema. The effect of ECMO support in critically ill animals showed contradicting results. ECMO support (further) induces endothelial damage, but endothelial activation does not, in the critically ill. Further research is necessary to conclude on the effect of the underlying comorbidity and type of ECMO support applied on endothelial dysfunction.

Using machine learning to predict neurologic injury in venovenous extracorporeal membrane oxygenation recipients: An ELSO Registry analysis

Background

Venovenous extracorporeal membrane oxygenation (VV-ECMO) is associated with acute brain injury (ABI), including central nervous system (CNS) ischemia (defined as ischemic stroke or hypoxic-ischemic brain injury [HIBI]) and intracranial hemorrhage (ICH). Data on prediction models for neurologic outcomes in VV-ECMO are limited.

Methods

We analyzed adult (age ≥18 years) VV-ECMO patients in the Extracorporeal Life Support Organization (ELSO) Registry (2009-2021) from 676 centers. ABI was defined as CNS ischemia, ICH, brain death, and seizures. Data on 67 variables were extracted, including clinical characteristics and pre-ECMO/on-ECMO variables. Random forest, CatBoost, LightGBM, and XGBoost machine learning (ML) algorithms (10-fold leave-one-out cross-validation) were used to predict ABI. Feature importance scores were used to pinpoint the most important variables for predicting ABI.

Results

Of 37,473 VV-ECMO patients (median age, 48.1 years; 63% male), 2644 (7.1%) experienced ABI, including 610 (2%) with CNS ischemia and 1591 (4%) with ICH. The areas under the receiver operating characteristic curve for predicting ABI, CNS ischemia, and ICH were 0.70, 0.68, and 0.70, respectively. The accuracy, positive predictive value, and negative predictive value for ABI were 85%, 19%, and 95%, respectively. ML identified higher center volume, pre-ECMO cardiac arrest, higher ECMO pump flow, and elevated on-ECMO serum lactate level as the most important risk factors for ABI and its subtypes.

Conclusions

This is the largest study of VV-ECMO patients to use ML to predict ABI reported to date. Performance was suboptimal, likely due to lack of standardization of neuromonitoring/imaging protocols and data granularity in the ELSO Registry. Standardized neurologic monitoring and imaging are needed across ELSO centers to detect the true prevalence of ABI.

Pulsatile flow increases METTL14-induced m 6 A modification and attenuates septic cardiomyopathy: an experimental study

INTRODUCTION

Septic cardiomyopathy is a sepsis-mediated cardiovascular complication with severe microcirculatory malperfusion. Emerging evidence has highlighted the protective effects of pulsatile flow in case of microcirculatory disturbance, yet the underlying mechanisms are still elusive. The objective of this study was to investigate the mechanisms of N 6 -methyladenosine (m 6 A) modification in the alleviation of septic cardiomyopathy associated with extracorporeal membrane oxygenation (ECMO)-generated pulsatile flow.

METHODS

Rat model with septic cardiomyopathy was established and was supported under ECMO either with pulsatile or non-pulsatile flow. Peripheral perfusion index (PPI) and cardiac function parameters were measured using ultrasonography. Dot blot assay was applied to examine the m 6 A level, while qRT-PCR, Western blot, immunofluorescence, and immunohistochemistry were used to measure the expressions of related genes. RNA immunoprecipitation assay was performed to validate the interaction between molecules.

RESULTS

The ECMO-generated pulsatile flow significantly elevates microcirculatory PPI, improves myocardial function, protects the endothelium, and prolongs survival in rat models with septic cardiomyopathy. The pulsatile flow mediates the METTL14-mediated m 6 A modification to zonula occludens-1 (ZO-1) mRNA (messenger RNA), which stabilizes the ZO-1 mRNA depending on the presence of YTHDF2. The pulsatile flow suppresses the PI3K-Akt signaling pathway, of which the downstream molecule Foxo1, a negative transcription factor of METTL14, binds to the METTL14 promoter and inhibits the METTL14-induced m 6 A modification.

CONCLUSION

The ECMO-generated pulsatile flow increases METTL14-induced m 6 A modification in ZO-1 and attenuates the progression of septic cardiomyopathy, suggesting that pulsatility might be a new therapeutic strategy in septic cardiomyopathy by alleviating microcirculatory disturbance.

Impact of Pulse Pressure on Acute Brain Injury in Venoarterial ECMO Patients with Cardiogenic Shock During the First 24 Hours of ECMO Cannulation: Analysis of the Extracorporeal Life Support Organization Registry

Background

Low pulse pressure (PP) in venoarterial-extracorporeal membrane oxygenation (VA-ECMO) is a marker of cardiac dysfunction and has been associated with acute brain injury (ABI) as continuous-flow centrifugal pump may lead to endothelial dysregulation.

Methods

We retrospectively analyzed adults (≥18 years) on "peripheral" VA-ECMO support for cardiogenic shock in the Extracorporeal Life Support Organization Registry (1/2018-7/2023). Cubic splines were used to establish a threshold (PP≤10 mmHg at 24 hours of ECMO support) for "early low" PP. ABI included central nervous system (CNS) ischemia, intracranial hemorrhage, brain death, and seizures. Multivariable logistic regressions were performed to examine whether PP≤10 mmHg was associated with ABI. Covariates included age, sex, body mass index, pre-ECMO variables (temporary mechanical support, vasopressors, cardiac arrest), on-ECMO variables (pH, PaO2, PaCO2), and on-ECMO complications (hemolysis, arrhythmia, renal replacement therapy).

Results

Of 9,807 peripheral VA-ECMO patients (median age=57.4 years, 67% male), 8,294 (85%) had PP>10 mmHg vs. 1,513 (15%) had PP≤10 mmHg. Patients with PP≤10 mmHg experienced ABI more frequently vs. PP>10 mmHg (15% vs. 11%, p<0.001). After adjustment, PP≤10 mmHg was independently associated with ABI (adjusted odds ratio [aOR]=1.25, 95% confidence interval [CI]=1.06-1.48, p=0.01). CNS ischemia and brain death were more common in patients with PP≤10 mmHg vs. PP>10 mmHg (8% vs. 6%, p=0.008; 3% vs. 1%, p<0.001). PP≤10 mmHg was associated with CNS ischemia (aOR=1.26, 95%CI=1.02-1.56, p=0.03) but not intracranial hemorrhage (aOR=1.14, 95%CI=0.85-1.54, p=0.38).

Conclusions

Early low PP (≤10 mmHg) at 24 hours of ECMO support was associated with ABI, particularly CNS ischemia, in peripheral VA-ECMO patients.