Recirculation during Veno-Venous Extra-Corporeal Membrane Oxygenation – a Simulation Study

The impact of hypovolemia and PEEP on recirculation in venovenous ECMO: an experimental porcine model

BACKGROUND

Recirculation is a common problem in venovenous extracorporeal membrane oxygenation (VV ECMO) and may limit the effect of ECMO treatment due to less efficient blood oxygenation or unfavorable ECMO and ventilator settings. The impact of hypovolemia and positive end expiratory pressure (PEEP) on recirculation is unclear and poorly described in guidelines, despite clinical importance. The aim of this study was to investigate how hypovolemia, autotransfusion and PEEP affect recirculation in comparison to ECMO cannula distance and circuit flow.

METHODS

In anesthetized and mechanically ventilated pigs (n = 6) on VV ECMO, we measured recirculation fraction (RF), changes in recirculation fraction (∆RF), hemodynamics and ECMO circuit pressures during alterations in PEEP (5 cmH2O vs 15 cmH2O), ECMO flow (3.5 L/min vs 5.0 L/min), cannula distance (10-14 cm vs 20-26 cm intravascular distance), hypovolemia (1000 mL blood loss) and autotransfusion (1000 mL blood transfusion).

RESULTS

Recirculation increased during hypovolemia (median ∆RF 43%), high PEEP (∆RF 28% and 12% with long and short cannula distance, respectively), high ECMO flow (∆RF 49% and 28% with long and short cannula distance, respectively) and with short cannula distance (∆RF 16%). Recirculation decreased after autotransfusion (∆RF - 45%).

CONCLUSIONS

In the present animal study, hypovolemia, PEEP and autotransfusion were important determinants of recirculation. The alterations were comparable to other well-known factors, such as ECMO circuit flow and intravascular cannula distance. Interestingly, hypovolemia increased recirculation without significant change in ECMO drainage pressure, whereas high PEEP increased recirculation with less negative ECMO drainage pressure. Autotransfusion decreased recirculation. The findings are interesting for clinical studies.

A computer model of the effect of venous-arterial-venous extracorporeal membrane oxygenation venous return of oxygenated blood on right atrial recirculation and tricuspid valve blood oxygen saturation

OBJECTIVE

Venous-arterial venous extracorporeal membrane oxygenation (V-AV ECMO), as a new clinical application of ECMO, showed great clinical application potential in the treatment of patients with combined cardiopulmonary failure. Given the complicated cannulation strategy of V-AV ECMO, its influence on the hemodynamics of the human circulatory system remained unclear.

METHODS

In this paper, a fluid-structure interaction was used to study the effect of V-AV ECMO oxygenated blood shunt ratio on right atrial recirculation and tricuspid valve (TV) blood oxygen saturation. In this study, the right atrium, superior vena cava supplying cannulae and inferior vena cava draining cannulae model of a specific patient was constructed. Seven cases with shunt ratio of 12.50%, 18.75%, 25.00%, 31.25%, 37.50%, 43.75% and 50.00% were designed.

RESULTS

The streamline diagram and velocity contour of oxygenated blood, recirculation fraction (RF), correlation of three variables (shunt ratio, RF, and oxygen saturation), and the oxygen saturation of blood at the TV were extracted for the study. Study results showed that, first, as the shunt ratio increased, the RF of the seven cases was 14.64%, 29.87%, 33.85%, 40.12%, 40.40%, 40.02%, and 38.09%. Second, with the increase of the shunt ratio, oxygen saturation of blood at the TV in seven cases was 82.1%, 82.5%, 83.3%, 83.3%, 84.0%, 84.6%, and 85.3%.

CONCLUSIONS

In this study, the shunt ratio had a strong correlation with the RF and oxygen saturation of blood at the TV. As the shunt ratio increased, the RF initially increased and then stabilized. However, oxygen saturation of blood at the TV would increase with the increase of the shunt ratio, but the degree of increase was small. This research provided useful information for surgeons and operators using V-AV ECMO.

Therapeutic Hypothermia for Refractory Hypoxemia on Venovenous Extracorporeal Membrane Oxygenation: An In Silico Study

Patients with respiratory failure may remain hypoxemic despite treatment with venovenous extracorporeal membrane oxygenation (VV-ECMO). Therapeutic hypothermia is a potential treatment for such hypoxia as it reduces cardiac output ( ) and oxygen consumption. We modified a previously published mathematical model of gas exchange to investigate the effects of hypothermia during VV-ECMO. Partial pressures were expressed as measured at 37°C (α-stat). The effect of hypothermia on gas exchange was examined in four clinical scenarios of hypoxemia on VV-ECMO, each with different physiological derangements. All scenarios had arterial partial pressure of oxygen (PaO 2 ) ≤ 46 mm Hg and arterial oxygen saturation of hemoglobin (SaO 2 ) ≤ 81%. Three had high with low extracorporeal blood flow to ratio ( ). The problem in the fourth scenario was recirculation, with normal . Cooling to 33°C increased SaO 2 to > 89% and PaO 2 to > 50 mm Hg in all scenarios. Mixed venous oxygen saturation of hemoglobin as % ( ) increased to > 70% and mixed venous partial pressure of oxygen in mm Hg ( ) increased to > 34 mm Hg in scenarios with low . In the scenario with high recirculation, and increased, but to < 50% and < 27 mm Hg, respectively. This in silico study predicted cooling to 33°C will improve oxygenation in refractory hypoxemia on VV-ECMO, but the improvement will be less when the problem is recirculation.

Device updates in pediatric and neonatal ECMO

Since the early use of extracorporeal life support (ECLS), new innovations and technological advancements have augmented the ability to use this technology in children and neonates. Cannulae have been re-designed to maintain structure and allow for single cannula venovenous (VV) ECLS in smaller patients. Circuit technology, including pumps and tubing, has evolved to permit smaller priming volumes and lower flow rates with fewer thrombotic or hemolytic complications. New oxygenator developments also improve efficiency of gas exchange. This paper serves as an overview of recent device developments in ECLS delivery to pediatric and neonatal patients.

Effects of changes in veno-venous extracorporeal membrane oxygenation blood flow on the measurement of intrathoracic blood volume and extravascular lung water index: a prospective interventional study

In severe acute respiratory distress syndrome (ARDS), veno-venous extracorporeal membrane oxygenation (V-V ECMO) has been proposed as a therapeutic strategy to possibly reduce mortality. Transpulmonary thermodilution (TPTD) enables monitoring of the extravascular lung water index (EVLWI) and cardiac preload parameters such as intrathoracic blood volume index (ITBVI) in patients with ARDS, but it is not generally recommended during V-V ECMO. We hypothesized that the amount of extracorporeal blood flow (ECBF) influences the calculation of EVLWI and ITBVI due to recirculation of indicator, which affects the measurement of the mean transit time (MTt), the time between injection and passing of half the indicator, as well as downslope time (DSt), the exponential washout of the indicator. EVLWI and ITBVI were measured in 20 patients with severe ARDS managed with V-V ECMO at ECBF rates from 6 to 4 and 2 l/min with TPTD. MTt and DSt significantly decreased when ECBF was reduced, resulting in a decreased EVLWI (26.1 [22.8-33.8] ml/kg at 6 l/min ECBF vs 22.4 [15.3-31.6] ml/kg at 4 l/min ECBF, p < 0.001; and 13.2 [11.8-18.8] ml/kg at 2 l/min ECBF, p < 0.001) and increased ITBVI (840 [753-1062] ml/m2 at 6 l/min ECBF vs 886 [658-979] ml/m2 at 4 l/min ECBF, p < 0.001; and 955 [817-1140] ml/m2 at 2 l/min ECBF, p < 0.001). In patients with severe ARDS managed with V-V ECMO, increasing ECBF alters the thermodilution curve, resulting in unreliable measurements of EVLWI and ITBVI. German Clinical Trials Register (DRKS00021050). Registered 14/08/2018. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00021050.

Simulators and Simulations for Extracorporeal Membrane Oxygenation: An ECMO Scoping Review

High-volume extracorporeal membrane oxygenation (ECMO) centers generally have better outcomes than (new) low-volume ECMO centers, most likely achieved by a suitable exposure to ECMO cases. To achieve a higher level of training, simulation-based training (SBT) offers an additional option for education and extended clinical skills. SBT could also help to improve the interdisciplinary team interactions. However, the level of ECMO simulators and/or simulations (ECMO sims) techniques may vary in purpose. We present a structured and objective classification of ECMO sims based on the broad experience of users and the developer for the available ECMO sims as low-, mid-, or high-fidelity. This classification is based on overall ECMO sim fidelity, established by taking the median of the definition-based fidelity, component fidelity, and customization fidelity as determined by expert opinion. According to this new classification, only low- and mid-fidelity ECMO sims are currently available. This comparison method may be used in the future for the description of new developments in ECMO sims, making it possible for ECMO sim designers, users, and researchers to compare accordingly, and ultimately improve ECMO patient outcomes.

The Impact of Recirculation on Extracorporeal Gas Exchange and Patient Oxygenation during Veno-Venous Extracorporeal Membrane Oxygenation-Results of an Observational Clinical Trial

Background: Recirculation during veno-venous extracorporeal membrane oxygenation reduces extracorporeal oxygen exchange and patient oxygenation. To minimize recirculation and maximize oxygen delivery (DO2) the interaction of cannulation, ECMO flow and cardiac output requires careful consideration. We investigated this interaction in an observational trial. Methods: In 19 patients with acute respiratory distress syndrome and ECMO, we measured recirculation with the ultrasound dilution technique and calculated extracorporeal oxygen transfer (VO2), extracorporeal oxygen delivery (DO2) and patient oxygenation. To assess the impact of cardiac output (CO), we included CO measurement through pulse contour analysis. Results: In all patients, there was a median recirculation rate of approximately 14−16%, with a maximum rate of 58%. Recirculation rates >35% occurred in 13−14% of all cases. In contrast to decreasing extracorporeal gas exchange with increasing ECMO flow and recirculation, patient oxygenation increased with greater ECMO flows. High CO diminished recirculation by between 5−20%. Conclusions: Extracorporeal gas exchange masks the importance of DO2 and its effects on patients. We assume that increasing DO2 is more important than reduced VO2. A negative correlation of recirculation to CO adds to the complexity of this phenomenon. Patient oxygenation may be optimized with the direct measurement of recirculation.

Recirculation in single lumen cannula venovenous extracorporeal membrane oxygenation: A non-randomized bi-centric trial

Background

Recirculation is a common problem in venovenous (VV) extracorporeal membrane oxygenation (ECMO). The aims of this study were to compare recirculation fraction (Rf) between femoro-jugular and jugulo-femoral VV ECMO configurations, to identify risk factors for recirculation and to assess the impact on hemolysis.

Methods

Patients in the medical intensive care unit (ICU) at the University Medical Center Regensburg, Germany receiving VV ECMO with femoro-jugular, and jugulo-femoral configuration at the ECMO Center Karolinska, Sweden, were included in this non-randomized prospective study. Total ECMO flow (QEC), recirculated flow (QREC), and recirculation fraction Rf = QREC/QEC were determined using ultrasound dilution technology. Effective ECMO flow (QEFF) was defined as QEFF = QEC * (1–Rf). Demographics, cannula specifics, and markers of hemolysis were assessed. Survival was evaluated at discharge from ICU.

Results

Thirty-seven patients with femoro-jugular configuration underwent 595 single-point measurements and 18 patients with jugulo-femoral configuration 231 measurements. Rf was lower with femoro-jugular compared to jugulo-femoral configuration [5 (0, 11) vs. 19 (13, 28) %, respectively (p &lt; 0.001)], resulting in similar QEFF [2.80 (2.21, 3.39) vs. 2.79 (2.39, 3.08) L/min (p = 0.225)] despite lower QEC with femoro-jugular configuration compared to jugulo-femoral [3.01 (2.40, 3.70) vs. 3.57 (3.05, 4.06) L/min, respectively (p &lt; 0.001)]. In multivariate regression analysis, the type of configuration, distance between the two cannula tips, ECMO flow, and heart rate were significantly associated with Rf [B (95% CI): 25.8 (17.6, 33.8), p &lt; 0.001; 960.4 (960.7, 960.1), p = 0.009; 4.2 (2.5, 5.9), p &lt; 0.001; 960.1 (960.2, 0.0), p = 0.027]. Hemolysis was similar in subjects with Rf &gt; 8 vs. ≤ 8%. Explorative data on survival showed comparable results in the femoro-jugular and the jugulo-femoral group (81 vs. 72%, p = 0.455).

Conclusion

VV ECMO with femoro-jugular configuration caused less recirculation. Further risk factors for higher Rf were shorter distance between the two cannula tips, higher ECMO flow, and lower heart rate. Rf did not affect hemolysis.

Extracorporeal Membrane Oxygenation Blood Flow and Blood Recirculation Compromise Thermodilution-Based Measurements of Cardiac Output

The contribution of veno-venous (VV) extracorporeal membrane oxygenation (ECMO) to systemic oxygen delivery is determined by the ratio of total extracorporeal blood flow () to cardiac output (). Thermodilution-based measurements of may be compromised by blood recirculating through the ECMO (recirculation fraction; Rf). We measured the effects of and Rf on classic thermodilution-based measurements of in six anesthetized pigs. An ultrasound flow probe measured total aortic blood flow () at the aortic root. Rf was quantified with the ultrasound dilution technique. was set to 0-125% of and was measured using a pulmonary artery catheter (PAC) in healthy and lung injured animals. PAC overestimated () at all settings compared to . The mean bias between both methods was 2.1 L/min in healthy animals and 2.7 L/min after lung injury. The difference between and increased with an of 75-125%/ compared to QEC <50%/. Overestimation of was highest when resulted in a high Rf. Thus, thermodilution-based measurements can overestimate cardiac output during VV ECMO. The degree of overestimation of depends on the EC/ ratio and the recirculation fraction.

Mathematical modelling of oxygenation under veno-venous ECMO configuration using either a femoral or a bicaval drainage

BACKGROUND

The bicaval drainage under veno-venous extracorporeal membrane oxygenation (VV ECMO) was compared in present experimental study to the inferior caval drainage in terms of systemic oxygenation.

METHOD

Two mathematical models were built to simulate the inferior vena cava-to-right atrium (IVC → RA) route and the bicaval drainage-to-right atrium return (IVC + SVC → RA) route using the following parameters: cardiac output (Q_C), IVC flow/Q_C ratio, venous oxygen saturation, extracorporeal pump flow (Q_EC), and pulmonary shunt (PULM-Shunt) to obtain pulmonary artery oxygen saturation (S_PAO₂) and systemic blood oxygen saturation (SaO₂).

RESULTS

With the IVC → RA route, S_PAO₂ and SaO₂ increased linearly with Q_EC/Q_C until the threshold of the IVC flow/Q_C ratio, beyond which the increase in S_PAO₂ reached a plateau. With the IVC + SVC → RA route, S_PAO₂ and SaO₂ increased linearly with Q_EC/Q_C until 100% with Q_EC/Q_C = 1. The difference in required Q_EC/Q_C between the two routes was all the higher as SaO₂ target or PULM-Shunt were high, and occurred all the earlier as PULM-Shunt were high. The required Q_EC between the two routes could differ from 1.0 L/min (Q_C = 5 L/min) to 1.5 L/min (Q_C = 8 L/min) for SaO₂ target = 90%. Corresponding differences of Q_EC for SaO₂ target = 94% were 4.7 L/min and 7.9 L/min, respectively.

CONCLUSION

Bicaval drainage under ECMO via the IVC + SVC → RA route gave a superior systemic oxygenation performance when both Q_EC/Q_C and pulmonary shunt were high. The VV-V ECMO configuration (IVC + SVC → RA route) might be an attractive rescue strategy in case of refractory hypoxaemia under VV ECMO.

In Vitro and In Vivo Feasibility Study for a Portable VV-ECMO and ECCO2R System

Extracorporeal membrane oxygenation (ECMO) is an established rescue therapy for patients with chronic respiratory failure waiting for lung transplantation (LTx). The therapy inherent immobilization may result in fatigue, consecutive deteriorated prognosis, and even lost eligibility for transplantation. We conducted a feasibility study on a novel system designed for the deployment of a portable ECMO device, enabling the physical exercise of awake patients prior to LTx. The system comprises a novel oxygenator with a directly connected blood pump, a double-lumen cannula, gas blender and supply, as well as control and energy management. In vitro experiments included tests regarding performance, efficiency, and blood damage. A reduced system was tested in vivo for feasibility using a novel large animal model. Six anesthetized pigs were first positioned in supine position, followed by a 45° angle, simulating an upright position of the patients. We monitored performance and vital parameters. All in vitro experiments showed good performance for the respective subsystems and the integrated system. The acute in vivo trials of 8 h duration confirmed the results. The novel portable ECMO-system enables adequate oxygenation and decarboxylation sufficient for, e.g., the physical exercise of designated LTx-recipients. These results are promising and suggest further preclinical studies on safety and efficacy to facilitate translation into clinical application.

Evaluation of Recirculation During Venovenous Extracorporeal Membrane Oxygenation Using Computational Fluid Dynamics Incorporating Fluid-Structure Interaction

Recirculation in venovenous extracorporeal membrane oxygenation (VV ECMO) leads to reduction in gas transfer efficiency. Studies of the factors contributing have been performed using in vivo studies and computational models. The fixed geometry of previous computational models limits the accuracy of results. We have developed a finite element computational fluid dynamics model incorporating fluid-structure interaction (FSI) that incorporates atrial deformation during atrial filling and emptying, with fluid flow solved using large eddy simulation. With this model, we have evaluated an extensive number of factors that could influence recirculation during two-site VV ECMO, and characterized their impact on recirculation, including cannula construction, insertion depth and orientation, VV ECMO configuration, circuit blood flow, and changes in volume, venous return, heart rate, and blood viscosity. Simulations revealed that extracorporeal blood flow relative to cardiac output, ratio of superior vena caval (SVC) to inferior vena caval (IVC) blood flow, position of the SVC cannula relative to the cavo-atrial junction, and orientation of the return cannula relative to the tricuspid valve had major influences (>20%) on recirculation fraction. Factors with a moderate influence on recirculation fraction (5%-20%) include heart rate, return cannula diameter, and direction of extracorporeal flow. Minimal influence on recirculation (<5%) was associated with atrial volume, position of the IVC cannula relative to the cavo-atrial junction, the number of side holes in the return cannula, and blood viscosity.

Structural recirculation and refractory hypoxemia under femoro-jugular veno-venous extracorporeal membrane oxygenation

The performance of each veno-venous extracorporeal membrane oxygenation (vv-ECMO) configuration is determined by the anatomic context and cannula position. A mathematical model was built considering bicaval specificities to simulate femoro-jugular configuration. The main parameters to define were cardiac output (Q_C ), blood flow in the superior vena cava (Q_SVC ), extracorporeal pump flow (Q_EC ), and pulmonary shunt (k_S-PULM ). The obtained variables were extracorporeal flow ratio in the superior vena cava (EFR_SVC  = Q_EC /[Q_EC  + Q_SVC ]), recirculation coefficient (R), effective extracorporeal pump flow (Q_eff-EC  = [1 - R] × Q_EC ), Q_eff-EC /Q_C ratio, and arterial blood oxygen saturation (SaO₂ ). EFR_SVC increased logarithmically when Q_EC increased. High Q_C or high Q_SVC /Q_C decreased EFR_SVC (range, 68%-85% for Q_EC of 5 L/min). R also increased following a logarithmic shape when Q_EC increased. The R rise was earlier and higher for low Q_C and high Q_SVC /Q_C (range, 12%-49% for Q_EC of 5 L/min). The Q_eff-EC /Q_C ratio (between 0 and 1) was equal to EFR_SVC for moderate and high Q_EC . The Q_eff-EC /Q_C ratio presented the same logarithmic profile when Q_EC increased, reaching a plateau (range, 0.67-0.91 for Q_EC /Q_C  = 1; range, 0.75-0.94 for Q_EC /Q_C  = 1.5). The Q_eff-EC /Q_C ratio was linearly associated with SaO₂ for a given pulmonary shunt. SaO₂  < 90% was observed when the pulmonary shunt was high (Q_eff-EC /Q_C  ≤ 0.7 with k_S-PULM  = 0.7 or Q_eff-EC /Q_C  ≤ 0.8 with k_S-PULM  = 0.8). Femoro-jugular vv-ECMO generates a systematic structural recirculation that gradually increases with Q_EC . EFR_SVC determines the Q_eff-EC /Q_C ratio, and thereby oxygen delivery and the superior cava shunt. EFR_SVC cannot exceed a limit value, explaining refractory hypoxemia in extreme situations.

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.

Right-Left Ventricular Interaction in Left-Sided Heart Failure With and Without Venoarterial Extracorporeal Membrane Oxygenation Support-A Simulation Study

Left ventricular (LV) dilatation is commonly seen with LV failure and is often aggravated during venoarterial extracorporeal membrane oxygenation (VA ECMO). In this context, the intricate interaction between left and right heart function is considered to be of pivotal importance, yet mechanistically not well understood. We hypothesize that a preserved or enhanced right heart contractility causes increased LV loading both with and without VA ECMO. A closed-loop in-silico simulation model containing the cardiac chambers, the pericardium, septal interactions, and the pulmonary and systemic vascular systems with an option to connect a simulated VA ECMO circuit was developed. Right ventricular contractility was modified during simulation of severe LV failure with and without VA ECMO. Left atrial pressures increased from 14.0 to 23.8 mm Hg without VA ECMO and from 18.4 to 27.0 mm Hg under VA ECMO support when right heart contractility was increased between end-systolic elastance 0.1 and 1.0 mm Hg/ml. Left-sided end-diastolic volumes increased from 125 to 169 ml without VA ECMO and from 150 to 180 ml with VA ECMO. Simulations demonstrate that increased diastolic loading of the LV may be driven by increased right ventricular contractility and that left atrial pressures cannot be interpreted as a reflection of the degree of LV dysfunction and overload without considering right ventricular function. Our study illustrates that modelling and computer simulation are important tools to unravel complex cardiovascular mechanisms underlying the right-left heart interdependency both with and without mechanical circulatory support.

Nitric Oxide Ventilation Improves Recirculation and Right Ventricular Function During Veno-Venous Extracorporeal Membrane Oxygenation in a COVID-19 Patient

Patients with coronavirus disease 2019 (COVID-19) are prone to pulmonary artery hypertension (PAH) and right ventricular pressure overload due to severe bilateral infiltrates, high ventilation pressures, persistent hypoxemia, pulmonary fibrosis, and/or pulmonary embolism. In patients on extracorporeal membrane oxygenation (ECMO), this potentially leads to increased recirculation. In the current report, the authors present a case in which continuous inhaled nitric oxide (iNO)-enriched ventilation was effective in terms of PAH and recirculation reduction in a COVID-19 patient on veno-venous ECMO.

Left Ventricular Unloading During Veno-Arterial ECMO: A Simulation Study

Supplemental Digital Content is available in the text.

Veno-arterial extracorporeal membrane oxygenation (VA ECMO) is widely used in cardiogenic shock. It provides systemic perfusion, but left ventricular (LV) unloading is suboptimal. Using a closed-loop, real-time computer model of the human cardiovascular system, cardiogenic shock supported by peripheral VA ECMO was simulated, and effects of various adjunct LV unloading interventions were quantified. After VA ECMO initiation (4 L/min) in cardiogenic shock (baseline), hemodynamics improved (increased to 85 mm Hg), while LV overload occurred (10% increase in end-diastolic volume [EDV], and 5 mm Hg increase in pulmonary capillary wedge pressure [PCWP]). Decreasing afterload (65 mm Hg mean arterial pressure) and circulating volume (−800 mL) reduced LV overload (12% decrease in EDV and 37% decrease in PCWP) compared with baseline. Additional intra-aortic balloon pumping only marginally decreased cardiac loading. Instead, adjunct Impella™ enhanced LV unloading (23% decrease in EDV and 41% decrease in PCWP). Alternative interventions, for example, left atrial/ventricular venting, yielded substantial unloading. We conclude that real-time simulations may provide quantitative clinical measures of LV overload, depending on the degree of VA ECMO support and adjunct management. Simulations offer insights into individualized LV unloading interventions in cardiogenic shock supported by VA ECMO as a proof of concept for potential future applications in clinical decision support, which may help to improve individualized patient management in complex cardiovascular disease.

Femoro-jugular cannulation in veno-venous extracorporeal membrane oxygenation PRO/CON

Veno-venous (VV) extracorporeal membrane oxygenation (ECMO) is the most efficient technique for respiratory support. It is based on a patient adequate circulation and cardiac function and it is indicated for isolated lung failure after optimization of the ventilatory support and the medical treatment. We describe PRO and CONs of the Femoro-jugular (F>J) approach, as an ideal setting for patients which require high flow (>5 L/min), such as those with extreme hypoxemia and/or septic shock. This technique can be accomplished very quickly at the bedside also in an unstable patient.

Perioperative Management of the Adult Patient on Venovenous Extracorporeal Membrane Oxygenation Requiring Noncardiac Surgery

The use of venovenous extracorporeal membrane oxygenation is increasing worldwide. These patients often require noncardiac surgery. In the perioperative period, preoperative assessment, patient transport, choice of anesthetic type, drug dosing, patient monitoring, and intraoperative and postoperative management of common patient problems will be impacted. Furthermore, common monitoring techniques will have unique limitations. Importantly, patients on venovenous extracorporeal membrane oxygenation remain subject to hypoxemia, hypercarbia, and acidemia in the perioperative setting despite extracorporeal support. Treatments of these conditions often require both manipulation of extracorporeal membrane oxygenation settings and physiologic interventions. Perioperative management of anticoagulation, as well as thresholds to transfuse blood products, remain highly controversial and must take into account the specific procedure, extracorporeal membrane oxygenation circuit function, and patient comorbidities. We will review the physiologic management of the patient requiring surgery while on venovenous extracorporeal membrane oxygenation.

Predictable capability control scheme for oxygen-exchange blood flow regulation in an extracorporeal membrane oxygenation system

Extracorporeal membrane oxygenation system is used for rescue treatment strategies for temporary cardiopulmonary function support to facilitate adequately oxygenated blood to return into the systemic and pulmonary circulation systems. Therefore, a servo flow regulator is used to adjust the roller motor speed, while support blood flow can match the sweep gas flow (GF) in a membrane oxygenator. A generalised regression neural network is designed as an estimator to automatically estimate the desired roller pump speed and control parameters. Then, the proportional-integral-derivative controller with tuning control parameters showed good performance to achieve speed regulation and speed tracking in the desired operating point. Given the pressure of carbon dioxide, drainage blood flow, and cannula size, the proposed predictable capability control scheme can be validated to meet the intended uses in clinical applications.

State of the Art: Bridging to lung transplantation using artificial organ support technologies

Lung transplantation increasingly is being performed in recipients of higher risk and acuity. A subset of these patients has severely abnormal gas exchange and/or right ventricular dysfunction, such that artificial organ support strategies are required to bridge patients to lung transplantation. We review the rationales and currently used and potential strategies for bridging to lung transplantation and characterize bridging outcomes. Based on physiologic reasoning and a study of the existing literature, we provide a working strategy for bridging to lung transplantation.

Adult venovenous extracorporeal membrane oxygenation for severe respiratory failure: Current status and future perspectives

Extracorporeal membrane oxygenation (ECMO) for severe acute respiratory failure was proposed more than 40 years ago. Despite the publication of the ARDSNet study and adoption of lung protective ventilation, the mortality for acute respiratory failure due to acute respiratory distress syndrome has continued to remain high. This technology has evolved over the past couple of decades and has been noted to be safe and successful, especially during the worldwide H1N1 influenza pandemic with good survival rates. The primary indications for ECMO in acute respiratory failure include severe refractory hypoxemic and hypercarbic respiratory failure in spite of maximum lung protective ventilatory support. Various triage criteria have been described and published. Contraindications exist when application of ECMO may be futile or technically impossible. Knowledge and appreciation of the circuit, cannulae, and the physiology of gas exchange with ECMO are necessary to ensure lung rest, efficiency of oxygenation, and ventilation as well as troubleshooting problems. Anticoagulation is a major concern with ECMO, and the evidence is evolving with respect to diagnostic testing and use of anticoagulants. Clinical management of the patient includes comprehensive critical care addressing sedation and neurologic issues, ensuring lung recruitment, diuresis, early enteral nutrition, treatment and surveillance of infections, and multisystem organ support. Newer technology that delinks oxygenation and ventilation by extracorporeal carbon dioxide removal may lead to ultra-lung protective ventilation, avoidance of endotracheal intubation in some situations, and ambulatory therapies as a bridge to lung transplantation. Risks, complications, and long-term outcomes and resources need to be considered and weighed in before widespread application. Ethical challenges are a reality and a multidisciplinary approach that should be adopted for every case in consideration.

Injection of agitated saline to detect recirculation with transthoracic echocardiography during venovenous extracorporeal oxygenation: A pilot study

PURPOSE

We assessed the security and efficiency of intravenously injected agitated saline in conjunction with transthoracic echocardiography to identify recirculation in patients supported with a venovenous extracorporeal membrane oxygenation (VV ECMO) device.

MATERIALS AND METHODS

We injected agitated saline 4 consecutive times separated by an interval of 5 minutes in 2 patients supported by VV ECMO. In both patients, the drainage cannula was placed in the left femoral vein, and the return cannula was placed in the right internal jugular vein. Echocardiography was performed during the injection and until the bubbles disappeared. The security of the method was assessed by evaluating the mechanical function of the ECMO and the efficiency of the oxygenator. The value of this method was assessed by visualizing the increase of inferior vena cava's echogenicity as well as by measuring the time required for this change to occur after the injection of agitated saline at different ECMO output levels.

RESULTS

We did not observe any change in ECMO, oxygenation function, or the hemodynamic status of patients after the 4 injections of agitated saline. The echogenicity of the inferior vena cava increased more rapidly as the ECMO's output increased. The recirculation phenomenon was noted even with low levels of ECMO output (<2 L/min).

CONCLUSIONS

Transthoracic echocardiography in conjunction with agitated saline administration may be a safe and easily applicable method to evaluate a recirculation phenomenon in patients supported with VV ECMO.

Veno-venous extracorporeal membrane oxygenation using an innovative dual-lumen cannula following implantation of a total artificial heart

We report our first clinical use of the new Protek Duo^TM cannula for peripheral veno-venous extra-corporeal life support (ECLS). A 53-year-old male patient underwent implantation of a total artificial heart (TAH) for biventricular failure. However, due to the development of post-operative respiratory dysfunction, the patient required ECLS for six days.

Venous Cannula Positioning in Arterial Deoxygenation During Veno-Arterial Extracorporeal Membrane Oxygenation-A Simulation Study and Case Report

Venoarterial extracorporeal membrane oxygenation (VA‐ECMO) is indicated in reversible life‐threatening circulatory failure with or without respiratory failure. Arterial desaturation in the upper body is frequently seen in patients with peripheral arterial cannulation and severe respiratory failure. The importance of venous cannula positioning was explored in a computer simulation model and a clinical case was described. A closed‐loop real‐time simulation model has been developed including vascular segments, the heart with valves and pericardium. ECMO was simulated with a fixed flow pump and a selection of clinically relevant venous cannulation sites. A clinical case with no tidal volumes due to pneumonia and an arterial saturation of below 60% in the right hand despite VA‐ECMO flow of 4 L/min was described. The case was compared with simulation data. Changing the venous cannulation site from the inferior to the superior caval vein increased arterial saturation in the right arm from below 60% to above 80% in the patient and from 64 to 81% in the simulation model without changing ECMO flow. The patient survived, was extubated and showed no signs of hypoxic damage. We conclude that venous drainage from the superior caval vein improves upper body arterial saturation during veno‐arterial ECMO as compared with drainage solely from the inferior caval vein in patients with respiratory failure. The results from the simulation model are in agreement with the clinical scenario.

Venovenous extracorporeal membrane oxygenation for acute respiratory failure : A clinical review from an international group of experts

Despite expensive life-sustaining interventions delivered in the ICU, mortality and morbidity in patients with acute respiratory failure (ARF) remain unacceptably high. Extracorporeal membrane oxygenation (ECMO) has emerged as a promising intervention that may provide more efficacious supportive care to these patients. Improvements in technology have made ECMO safer and easier to use, allowing for the potential of more widespread application in patients with ARF. A greater appreciation of the complications associated with the placement of an artificial airway and mechanical ventilation has led clinicians and researchers to seek viable alternatives to providing supportive care in these patients. Thus, this review will summarize the current knowledge regarding the use of venovenous (VV)-ECMO for ARF and describe some of the recent controversies in the field, such as mechanical ventilation, anticoagulation and transfusion therapy, and ethical concerns in patients supported with VV-ECMO.

Individualized real-time clinical decision support to monitor cardiac loading during venoarterial ECMO

Veno-arterial extracoporeal membrane oxygenation (VA ECMO) is increasingly used for acute and refractory cardiogenic shock. Yet, in clinical practice, monitoring of cardiac loading conditions during VA ECMO can be cumbersome. To this end, we illustrate the validity and clinical applicability of a real-time cardiovascular computer simulation, which allows to integrate hemodynamics, cardiac dimensions and the corresponding degree of VA ECMO support and ventricular loading in individual patients over time.

Extracorporeal membrane oxygenation: a breakthrough for respiratory failure

Extracorporeal membrane oxygenation (ECMO) is a method for providing long-term treatment of a patient in a modified heart-lung machine. Desaturated blood is drained from the patient, oxygenated and pumped back to a major vein or artery. ECMO supports heart and lung function and may be used in severe heart and/or lung failure when conventional intensive care fails. The Stockholm programme started in 1987 with treatment of neonates. In 1995, the first adult patient was accepted onto the programme. Interhospital transportation during ECMO was started in 1996, which enabled retrieval of extremely unstable patients during ECMO. Today, the programme has an annual volume of about 80 patients. It has been characterized by, amongst other things, minimal patient sedation. By 31 December 2014, over 900 patients had been treated, the vast majority for respiratory failure, and over 650 patients had been transported during ECMO. The median ECMO duration was 5.3, 5.7 and 7.1 days for neonatal, paediatric and adult patients, respectively. The survival to hospital discharge rate for respiratory ECMO was 81%, 70% and 63% in the different age groups, respectively, which is significantly higher than the overall international experience as reported to the Extracorporeal Life Support Organization (ELSO) Registry (74%, 57% and 57%, respectively). The survival rate was significantly higher in the Stockholm programme compared to ELSO for meconium aspiration syndrome, congenital diaphragmatic hernia in neonates and pneumocystis pneumonia in paediatric patients.

Hybrid ECMO for a patient in respiratory failure developing cardiac insufficiency

A 45-year-old patient in lung failure treated with veno-venous extracorporeal membrane oxygenation (VV ECMO) developed subsequent right heart failure and required cardiac support.

We present a method of upgrading a VV ECMO to a hybrid system for simultaneous support for respiratory and cardiac failure.