Cannula Design and Recirculation During Venovenous Extracorporeal Membrane Oxygenation

Numerical Study of the Effect of the Port Angle of the Superior Vena Cava Supplying Cannula on Hemodynamics in the Right Atrium in VV-ECMO

Objective: To elucidate the pattern of the influence of the port angle of the superior vena cava supplying cannula (SVCS) on hemodynamics within the right atrium in VV-ECMO. Methods: A three-dimensional model of the right atrium was established based on CT images of a real patient. The 3D models of the SVCS and inferior vena cava draining cannula (IVCD) were established based on the Edwards 18Fr and Medos 22Fr real intubation models, respectively. Based on these models, three-dimensional models of the SVCS ports with bending angles of -90°, -60°, -30°, 0°, 30°, 60°, and 90° in the plane formed by the centerline of the SVCS and the center point of the tricuspid valve (TV) were established. Transient-state computational fluid dynamics (CFD) was performed to clarify the right atrium blood flow pattern and hemodynamic states at different SVCS port orientation angles. The velocity clouds, wall pressure, wall shear stress (WSS), relative residence time (RRT), and recirculation fraction (RF) were calculated to assess hemodynamic changes in the right atrium at different angles of the port of the SVCS. Results: As the angle of the port of the superior chamber cannula changed, the location of the high-velocity blood impingement from the SVCS changed, and the pattern of blood flow within the right atrium was dramatically altered. The results for the maximum right atrial wall pressure were 13,472 pa, 13,424 pa, 10,915 pa, 7680.2 pa, 5890.3 pa, 5597.6 pa, and 7883.5 pa (-90° vs. -60° vs. -30° vs. 0° vs. 30° vs. 60° vs. 90°), and the results for the mean right atrial wall pressure were 6788.9 pa, 8615.1 pa, 8684.9 pa, 6717.2 pa, 5429.2 pa, 5455.6 pa, and 7117.8 pa ( -90° vs. -60° vs. -30° vs. 0° vs. 30° vs. 60° vs. 90°). The results of the maximum right atrial wall WSS in the seven cases were 63.572 pa, 55.839 pa, 31.705 pa, 39.531 pa, 40.11 pa, 28.474 pa, and 35.424 (-90° vs. -60° vs. -30° vs. 0° vs. 30° vs. 60° vs. 90°), respectively, and the results of the mean right atrial wall WSS results were 3.8589 pa, 3.6706 pa, 3.3013 pa, 3.2487 pa, 2.3995 pa, 1.3304 pa, and 2.0747 pa (-90° vs. -60° vs. -30° vs. 0° vs. 30° vs. 60° vs. 90°), respectively. The results for the area percentage of high RRT in the seven cases were 3.44%, 2.23%, 4.24%, 1.83%, 3.69%, 7.73%, and 3.68% (-90° vs. -60° vs. -30° vs. 0° vs. 30° vs. 60° vs. 90°), and the results for the RF were 21.57%, 23.24%, 19.78%, 12.57%, 10.24%, 5.07%, and 8.05% (-90° vs. -60° vs. -30° vs. 0° vs. 30° vs. 60° vs. 90°). Conclusions: The more the port of the SVCS is oriented toward the TV, the more favorable it is for reducing RF and the impingement of blood flow in the right atrial wall, but there may be an increased risk of RRT. The opposite orientation of the SVCS port to the TV is not conducive to reducing flow impingement on the right atrial wall and RF.

Beta-blockade for the treatment of refractory hypoxaemia during venovenous extracorporeal membrane oxygenation: An in-silico study

INTRODUCTION

Venovenous extracorporeal membrane oxygenation (VV ECMO) is used for refractory hypoxemia, although despite this, in high cardiac output states, hypoxaemia may persist. The administration of beta-blockers has been suggested as an approach in this scenario, however the physiological consequences of this intervention are not clear.

METHODS

We performed an in-silico study using a previously described mathematical model to evaluate the effect of beta-blockade on mixed venous and arterial saturations (S v ¯ O 2 , SaO2), in three different clinical scenarios and considered the potential effects of beta-blockers on, cardiac output, oxygen consumption and recirculation. Additionally we assessed the interaction of beta-blockade with haemoglobin concentration.

RESULTS

In scenario 1: simulating a patient with high cardiac output and partial lung shunt S v ¯ O 2 decreased from increased 53.5% to 44.7% despite SaO2 rising from 74.2% to 79.2%. In scenario 2 simulating a patient with high cardiac output and complete lung shunt S v ¯ O 2 remained unchanged at 52.2% and SaO2 rose from 71.9% to 85%. In scenario 3 a patient with normal cardiac output and high recirculation S v ¯ O 2 fell from 50.8% to 25.5% and also fell from 82.4% to to 78.3%. Across the remaining modelling examples the effect on S v ¯ O 2 varied but oxygen delivery was consistently reduced across all scenarios.

CONCLUSION

The administration of beta-blockers for refractory hypoxemia during VV ECMO are unpredictable and may reduce oxygen delivery, although this will vary with patient and circuit features. This study does not support the use of beta-blockers for this indication.

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.

Outcomes following additional drainage during veno-venous extracorporeal membrane oxygenation: A single-center retrospective study

Refractory hypoxemia during veno-venous (V-V) extracorporeal membrane oxygenation (ECMO) may require an additional cannula (VV-V ECMO) to improve oxygenation. This intervention includes risk of recirculation and other various adverse events (AEs) such as injury to the lung, cannula malpositioning, bleeding, circuit or cannula thrombosis requiring intervention (i.e., clot), or cerebral injury. During the study period, 23 of 142 V-V ECMO patients were converted to VV-V utilizing two separate cannulas for bi-caval drainage with an additional upper extremity cannula placed for return. Of those, 21 had COVID-19. In the first 24 h after conversion, ECMO flow rates were higher (5.96 vs 5.24 L/min, p = .002) with no significant change in pump speed (3764 vs 3630 revolutions per minute [RPMs], p = .42). Arterial oxygenation (PaO2) increased (87 vs 64 mmHg, p < .0001) with comparable pre-oxygenator venous saturation (61 vs 53.3, p = .12). By day 5, flows were similar to pre-conversion values at lower pump speed but with improved PaO2. Unadjusted survival was similar in those converted to VV-V ECMO compared to V-V ECMO alone (70% [16/23] vs 66.4% [79/119], p = .77). In a mixed effect regression model, any incidence of AEs, demonstrated a negative impact on PaO2 in the first 48 h but not at day 5. VV-V ECMO improved oxygenation with increasing flows without a significant difference in AEs or pump speed. AEs transiently impacted oxygenation. VV-V ECMO is effective and feasible strategy for refractory hypoxemia on VV-ECMO allowing for higher flow rate and unchanged pump speed.

The intricate physiology of veno-venous extracorporeal membrane oxygenation: an overview for clinicians

During veno-venous extracorporeal membrane oxygenation (V-V ECMO), blood is drained from the central venous circulation to be oxygenated and decarbonated by an artificial lung. It is then reinfused into the right heart and pulmonary circulation where further gas-exchange occurs. Each of these steps is characterized by a peculiar physiology that this manuscript analyses, with the aim of providing bedside tools for clinical care: we begin by describing the factors that affect the efficiency of blood drainage, such as patient and cannulae position, fluid status, cardiac output and ventilatory strategies. We then dig into the complexity of extracorporeal gas-exchange, with particular reference to the effects of extracorporeal blood-flow (ECBF), fraction of delivered oxygen (FdO2) and sweep gas-flow (SGF) on oxygenation and decarbonation. Subsequently, we focus on the reinfusion of arterialized blood into the right heart, highlighting the effects on recirculation and, more importantly, on right ventricular function. The importance and challenges of haemodynamic monitoring during V-V ECMO are also analysed. Finally, we detail the interdependence between extracorporeal circulation, native lung function and mechanical ventilation in providing adequate arterial blood gases while allowing lung rest. In the absence of evidence-based strategies to care for this particular group of patients, clinical practice is underpinned by a sound knowledge of the intricate physiology of V-V ECMO.

In silico parametric analysis of femoro-jugular venovenous ECMO and return cannula dynamics: In silico analysis of femoro-jugular VV ECMO

BACKGROUND

Increasingly, computational fluid dynamics (CFD) is helping explore the impact of variables like: cannula design/size/position/flow rate and patient physiology on venovenous (VV) extracorporeal membrane oxygenation (ECMO). Here we use a CFD model to determine what role cardiac output (CO) plays and to analyse return cannula dynamics.

METHODS

Using a patient-averaged model of the right atrium and venae cava, we virtually inserted a 19Fr return cannula and a 25Fr drainage cannula. Running large eddy simulations, we assessed cardiac output at: 3.5-6.5 L/min and ECMO flow rate at: 2-6 L/min. We analysed recirculation fraction (Rf), time-averaged wall shear stress (TAWSS), pressure, velocity, and turbulent kinetic energy (TKE) and extracorporeal flow fraction (EFF = ECMO flow rate/CO).

RESULTS

Increased ECMO flow rate and decreased CO (high EFF) led to increased Rf (R = 0.98, log fit). Negative pressures developed in the venae cavae at low CO and high ECMO flow (high CR). Mean return cannula TAWSS was >10 Pa for all ECMO flow rates, with majority of the flow exiting the tip (94.0-95.8 %).

CONCLUSIONS

Our results underpin the strong impact of CO on VV ECMO. A simple metric like EFF, once supported by clinical data, might help predict Rf for a patient at a given ECMO flow rate. The return cannula imparts high shear stresses on the blood, largely a result of the internal diameter.

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.

Alternative position of cannulae in veno-venous extracorporeal membrane oxygenation for maintaining sufficient flow support

Blood flow disturbance of veno-venous extracorporeal membrane oxygenation (VV-ECMO) can be a risk factor of weaning failure. We report an alternative position of cannulae of VV-ECMO which can maintain blood flow. The recirculation rate could be controlled by adjusting a position of return cannula using dilutional ultrasound monitoring.

The physiology of extracorporeal membrane oxygenation: The Fick principle

Extracorporeal membrane oxygenation (ECMO) can be delivered in veno-arterial (VA) and veno-venous (VV) configurations based on the cannulation strategy. VA and VV ECMO are delivered primarily for haemodynamic and respiratory support in patients with severe heart and lung failure, respectively. The Fick principle describes the relationship between blood flow and oxygen consumption - key parameters in the physiological management of extracorporeal support. This review will discuss the application of the Fick principle in: (i) recirculation in VV ECMO; (ii) the quantification of oxygen delivery (DO2) in VV ECMO and (iii) the quantification of transpulmonary blood flow and systemic arterial oxygen saturation in VA ECMO.

Improved Flow Dynamics of Extracorporeal Membrane Oxygenation via Design Modification of Dual-Lumen Cannulas

Veno-venous extracorporeal membrane oxygenation (VV-ECMO) supports patients with severe respiratory failure not responding to conventional treatments. Single-site jugular venous cannulation with dual-lumen cannulas (DLC) have several advantages over traditional single-lumen cannulas, however, bleeding and thrombosis are common, limiting their clinical utility. This study numerically investigated the effects of DLC side holes on blood flow dynamics since the maximum wall shear stress (WSS) occurs around the side holes. A DLC based on the Avalon Elite 27Fr model was implanted into an idealized 3D model of the vena cava and right atrium (RA). Eight DLCs were developed by changing the number, diameter, and spacing of side holes through an iterative design process. Physiologic flow at the inferior vena cava (IVC) and superior vena cava (SVC) were applied along with a partial ECMO support of 2 L/min. The SST k-ω turbulent model was solved for 6.4 seconds. WSS, washout, stagnation volume, and recirculation were compared. For all DLCs, no stasis region lasted more than one cardiac cycle and a complete washout was obtained in less than 4 seconds. Due to the IVC and SVC backflows, maximum WSS occurred around the DLC side holes at late systole and late diastole. A DLC with 16 and three side holes within the IVC and SVC, respectively, reduced the maximum WSS by up to 67% over the Avalon Elite 27Fr. Improved DLCs provided a more uniform WSS distribution with lower WSS around the side holes, potentially reducing the chance of thrombosis and bleeding.

Cannulation configuration and recirculation in venovenous extracorporeal membrane oxygenation

Venovenous extracorporeal membrane oxygenation is a treatment for acute respiratory distress syndrome. Femoro-atrial cannulation means blood is drained from the inferior vena cava and returned to the superior vena cava; the opposite is termed atrio-femoral. Clinical data comparing these two methods is scarce and conflicting. Using computational fluid dynamics, we aim to compare atrio-femoral and femoro-atrial cannulation to assess the impact on recirculation fraction, under ideal conditions and several clinical scenarios. Using a patient-averaged model of the venae cavae and right atrium, commercially-available cannulae were positioned in each configuration. Additionally, occlusion of the femoro-atrial drainage cannula side-holes with/without reduced inferior vena cava inflow (0-75%) and retraction of the atrio-femoral drainage cannula were modelled. Large-eddy simulations were run for 2-6L/min circuit flow, obtaining time-averaged flow data. The model showed good agreement with clinical atrio-femoral recirculation data. Under ideal conditions, atrio-femoral yielded 13.5% higher recirculation than femoro-atrial across all circuit flow rates. Atrio-femoral right atrium flow patterns resembled normal physiology with a single large vortex. Femoro-atrial cannulation resulted in multiple vortices and increased turbulent kinetic energy at > 3L/min circuit flow. Occluding femoro-atrial drainage cannula side-holes and reducing inferior vena cava inflow increased mean recirculation by 11% and 32%, respectively. Retracting the atrio-femoral drainage cannula did not affect recirculation. These results suggest that, depending on drainage issues, either atrio-femoral or femoro-atrial cannulation may be preferrable. Rather than cannula tip proximity, the supply of available venous blood at the drainage site appears to be the strongest factor affecting 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.

Quantification of Recirculation During Veno-Venous Extracorporeal Membrane Oxygenation: In Vitro Evaluation of a Thermodilution Technique

Veno-venous extracorporeal membrane oxygenation (vv-ECMO) represents one of the most advanced respiratory support for patients suffering from severe acute respiratory distress syndrome. During vv-ECMO a certain amount of extracorporeal oxygenated blood can flow back from the reinfusion into the drainage cannula without delivering oxygen to the patient. Detection and quantification of this dynamic phenomenon, defined recirculation, are critical to optimize the ECMO efficiency. Our study aimed to measure the recirculation fraction (RF) using a thermodilution technique. We built an in vitro circuit to simulate patients undergoing vv-ECMO (ECMO flow: 1.5, 3, and 4.5 L/min) with different cardiac output, using a recirculation bridge to achieve several known RFs (from 0% to 50%). The RF, computed as the ratio of the area under temperature-time curves (AUC) of the drainage and reinfusion, was significantly related to the set RF (AUC ratio (%) = 0.979 × RF (%) + 0.277%, p < 0.0001), but it was not dependent on tested ECMO and cardiac output values. A Bland-Altman analysis showed an AUC ratio bias (precision) of -0.21% for the overall data. Test-retest reliability showed an intraclass correlation coefficient of 0.993. This study proved the technical feasibility and computation validity of the applied thermodilution technique in computing vv-ECMO RF.

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.

Imaging for Temporary Mechanical Circulatory Support Devices

Heart failure is an important cause of mortality and morbidity in the world. Changes in organ allocation for solid thoracic (lung and heart) transplantation has increased the number of patients on mechanical circulatory support. Temporary mechanical support devices include devices tht support the circulation directly or indirectly such as extracorporeal membrane oxygenation (ECMO) and temporary support for right-sided failure, left-sided failure or biventricular failure. Most often, these devices are placed percutaneously and require either guidance with echocardiography, continuous radiography (fluoroscopy) or both. Furthermore, these devices need imaging in the intensive care unit to confirm continued accurate placement. This review contains the imaging views and nuances of the temporary assist devices (including ECMO) at the time of placement and the complications that can be associated with each individual device.

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.

Transpulmonary thermodilution in patients treated with veno-venous extracorporeal membrane oxygenation

BACKGROUND

We tested the effect of different blood flow levels in the extracorporeal circuit on the measurements of cardiac stroke volume (SV), global end-diastolic volume index (GEDVI) and extravascular lung water index derived from transpulmonary thermodilution (TPTD) in 20 patients with severe acute respiratory distress syndrome (ARDS) treated with veno-venous extracorporeal membrane oxygenation (ECMO).

METHODS

Comparative SV measurements with transesophageal echocardiography and TPTD were performed at least 5 times during the treatment of the patients. The data were interpreted with a Bland-Altman analysis corrected for repeated measurements. The interchangeability between both measurement modalities was calculated and the effects of extracorporeal blood flow on SV measurements with TPTD was analysed with a linear mixed effect model. GEDVI and EVLWI measurements were performed immediately before the termination of the ECMO therapy at a blood flow of 6 l/min, 4 l/min and 2 l/min and after the disconnection of the circuit in 7 patients.

RESULTS

170 pairs of comparative SV measurements were analysed. Average difference between the two modalities (bias) was 0.28 ml with an upper level of agreement of 40 ml and a lower level of agreement of -39 ml within a 95% confidence interval and an overall interchangeability rate between TPTD and Echo of 64%. ECMO blood flow did not influence the mean bias between Echo and TPTD (0.03 ml per l/min of ECMO blood flow; p = 0.992; CI - 6.74 to 6.81). GEDVI measurement was not significantly influenced by the blood flow in the ECMO circuit, whereas EVLWI differed at a blood flow of 6 l/min compared to no ECMO flow (25.9 ± 10.1 vs. 11.0 ± 4.2 ml/kg, p = 0.0035).

CONCLUSIONS

Irrespectively of an established ECMO therapy, comparative SV measurements with Echo and TPTD are not interchangeable. Such caveats also apply to the interpretation of EVLWI, especially with a high blood flow in the extracorporeal circulation. In such situations, the clinician should rely on other methods of evaluation of the amount of lung oedema with the haemodynamic situation, vasopressor support and cumulative fluid balance in mind.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00021050). Registered 03/30/2020 https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00017237.

Awake Extracorporeal Membrane Oxygenation for Acute Respiratory Distress Syndrome: Which Clinical Issues Should Be Taken Into Consideration

With the goal of protecting injured lungs and extrapulmonary organs, venovenous extracorporeal membrane oxygenation (VV-ECMO) has been increasingly adopted as a rescue therapy for patients with severe acute respiratory distress syndrome (ARDS) when conventional mechanical ventilation failed to provide effective oxygenation and decarbonation. In recent years, it has become a promising approach to respiratory support for awake, non-intubated, spontaneously breathing patients with respiratory failure, referred to as awake ECMO, to avoid possible detrimental effects associated with intubation, mechanical ventilation, and the adjunctive therapies. However, several complex clinical issues should be taken into consideration when initiating and implementing awake ECMO, such as selecting potential patients who appeared to benefit most; techniques to facilitating cannulation and maintain stable ECMO blood flow; approaches to manage pain, agitation, and delirium; and approaches to monitor and modulate respiratory drive. It is worth mentioning that there had also been some inherent disadvantages and limitations of awake ECMO compared to the conventional combination of ECMO and invasive mechanical ventilation. Here, we review the use of ECMO in awake, spontaneously breathing patients with severe ARDS, highlighting the issues involving bedside clinical practice, detailing some of the technical aspects, and summarizing the initial clinical experience gained over the past years.

Extracorporeal Membrane Oxygenation Use in Thoracic Surgery

This narrative review is focused on the application of extracorporeal membrane oxygenation (ECMO) in thoracic surgery, exclusive of lung transplantation. Although the use of ECMO in this indication is still rare, it allows surgery to be performed in patients where conventional ventilation is not feasible-especially in single lung patients, sleeve lobectomy or pneumonectomy and tracheal or carinal reconstructions. Comparisons with other techniques, various ECMO configurations, the management of anticoagulation, anesthesia, hypoxemia during surgery and the use of ECMO in case of postoperative respiratory failure are reviewed and supported by two cases of perioperative ECMO use, and an overview of published case series.

Hemodynamic performance limits of the neonatal Double-Lumen cannula

Venovenous extracorporeal membrane oxygenation (VV-ECMO) is the preferred surgical intervention for patients suffering from severe cardiorespiratory failure, also encountered in SARS-Cov-2 management. The key component of VV-ECMO is the double-lumen cannula (DLC) that enables single-site access. The biofluid dynamics of this compact device is particularly challenging for neonatal patients due to high Reynolds numbers, tricuspid valve location and right-atrium hemodynamics. In this paper we present detailed findings of our comparative analysis of the right-atrial hemodynamics and salient design features of the 13Fr Avalon Elite DLC (as the clinically preferred neonatal cannula) with the alternate Origen DLC design, using experimentally validated computational fluid dynamics. Highly accurate 3D-reconstructions of both devices were obtained through an integrated optical coherence tomography and micro-CT imaging approach. Both cannula configurations displayed complex flow structures inside the atrium, superimposed over predominant recirculation regimes. We found that the Avalon DLC performed significantly better than the Origen alternative, by capturing 80% and 94% of venous blood from the inferior and superior vena cavae, respectively and infusing the oxygenated blood with an efficiency of more than 85%. The micro-scale geometric design features of the Avalon DLC that are associated with superior hemodynamics were investigated through 14 parametric cannula configurations. These simulations showed that the strategic placement of drainage holes, the smooth infusion blood stream diverter and efficient distribution of the venous blood capturing area between the vena cavae are associated with robust blood flow performance. Nevertheless, our parametric results indicate that there is still room for further device optimization beyond the performance measurements for both Avalon and Origen DLC in this study. In particular, the performance envelope of malpositioned cannula and off-design conditions require additional blood flow simulations for analysis.

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.

Veno-Venous Extracorporeal Membrane Oxygenation in COVID-19-Where Are We Now?

The recent development in extracorporeal life support (ECLS) has created new therapeutic opportunities for critically ill patients. An interest in extracorporeal membrane oxygenation (ECMO), the pinnacle of ECLS techniques, has recently increased, as for the last decade, we have observed improvements in the survival of patients suffering from severe acute respiratory distress syndrome (ARDS) while on ECMO. Although there is a paucity of conclusive data from clinical research regarding extracorporeal oxygenation in COVID-19 patients, the pathophysiology of the disease makes veno-venous ECMO a promising option.

Comparison of atrio-femoral and femoro-atrial venovenous extracorporeal membrane oxygenation in adult

INTRODUCTION

Different cannulation approaches existed for veno-venous extracorporeal membrane oxygenation (VV ECMO). We aimed to compare the atrio-femoral (AF) and femoro-atrial (FA) configuration in terms of their flow efficiency and influence on patient outcome.

METHOD

This was a single-centre, retrospective case control study. Adult patients admitted to the Intensive Care Unit and required VV ECMO service at Tuen Mun Hospital, Hong Kong, from June 2015 to January 2020 were included. Data were collected from our ECMO database for comparison.

RESULTS

Between June 2015 and January 2020, eight patients received AF configuration and 19 patients received FA configuration. The maximum achieved flow in the AF group was significantly higher than that in the FA group (4.08 ± 0.57 L/min vs. 3.52 ± 0.58 L/min, p = 0.03). The fluid balance in first 3 days of ECMO was significantly lower in the AF group compared to that in the FA group (1.16 ± 2.71 L vs. 3.46 ± 1.97 L, p = 0.02). As well, the chance for successful awake ECMO was statistically higher in the AF group (p = 0.048).

CONCLUSION

Atrio-femoral configuration in VV ECMO was associated with a higher maximum achieved ECMO flow, less fluid gain in first 3 days of ECMO and more successful awake ECMO.

Veno-arterio-pulmonary-arterial extracorporeal membrane oxygenation in descending aortic surgery

Hypoxia during one-lung ventilation is a significant problem in descending aortic surgery via left thoracotomy. Veno-arterio-pulmonary-arterial extracorporeal membrane oxygenation (VAPa-ECMO), which consists of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) and an additional arterial branch to perfuse a pulmonary artery (Pa), is useful.

Extracorporeal Membrane Oxygenation for Respiratory Failure

This review focuses on the use of veno-venous extracorporeal membrane oxygenation for respiratory failure across all blood flow ranges. Starting with a short overview of historical development, aspects of the physiology of gas exchange (i.e., oxygenation and decarboxylation) during extracorporeal circulation are discussed. The mechanisms of phenomena such as recirculation and shunt playing an important role in daily clinical practice are explained.Treatment of refractory and symptomatic hypoxemic respiratory failure (e.g., acute respiratory distress syndrome [ARDS]) currently represents the main indication for high-flow veno-venous-extracorporeal membrane oxygenation. On the other hand, lower-flow extracorporeal carbon dioxide removal might potentially help to avoid or attenuate ventilator-induced lung injury by allowing reduction of the energy load (i.e., driving pressure, mechanical power) transmitted to the lungs during mechanical ventilation or spontaneous ventilation. In the latter context, extracorporeal carbon dioxide removal plays an emerging role in the treatment of chronic obstructive pulmonary disease patients during acute exacerbations. Both applications of extracorporeal lung support raise important ethical considerations, such as likelihood of ultimate futility and end-of-life decision-making. The review concludes with a brief overview of potential technical developments and persistent challenges.

Clinical outcomes according to cannula configurations in patients with acute respiratory distress syndrome under veno-venous extracorporeal membrane oxygenation: a Korean multicenter study

BACKGROUND

Recirculation during veno-venous extracorporeal membrane oxygenation (VV-ECMO) is a known drawback that limits sufficient oxygenation. This study aimed to compare the short-term oxygenation and long-term mortality based on cannula configuration in patients with acute respiratory distress syndrome (ARDS) who receive VV-ECMO, especially in the absence of newly developed dual-lumen, single cannula.

METHODS

Data of patients with severe ARDS who received VV-ECMO from 2012 to 2015 at six hospitals were retrospectively analyzed. Primary outcomes were the partial pressure of oxygen (PaO₂) at 1, 4, and 12 h after ECMO initiation and 180-day mortality.

RESULTS

Patients (n = 335) were divided into two groups based on the return cannula site: femoral vein (n = 178) or internal jugular vein (n = 157). The propensity score matching analysis generated 90 pairs, and baseline characteristics at admission, including PaO₂, were similar between the groups. PaO₂ at 1, 4 and 12 h after ECMO initiation were not different according to cannula configuration. Moreover, the increment in oxygenation from the baseline values was not different between the femoral and jugular group. PaCO₂ level at 1, 4 and 12 h were significantly lower in the jugular group. The two groups did not differ in terms of mortality at 180 days after ECMO, however more cannula-related complications occurred in the jugular group.

CONCLUSION

Regardless of the cannula configuration, patients with ARDS managed with VV-ECMO showed comparable clinical outcomes in terms of short-term oxygenation and long-term mortality. Nevertheless, further well-designed randomized control trials are warranted.

Pressure and flow properties of dual-lumen cannulae for extracorporeal membrane oxygenation

INTRODUCTION

In the last decade, dual-lumen cannulae have been increasingly applied in patients undergoing extracorporeal life support. Well-performing vascular access is crucial for efficient extracorporeal membrane oxygenation support; thus, guidance for proper cannulae size is required. Pressure-flow charts provided by manufacturers are often based on tests performed using water, rarely blood. However, blood is a shear-thinning and viscoelastic fluid characterized by different flow properties than water.

METHODS

We performed a study evaluating pressure-flow curves during standardized conditions using human whole blood in two commonly available dual-lumen cannulae used in neonates, pediatric, and adult patients. Results were merged and compared with the manufacturer's corresponding curves obtained from the public domain.

RESULTS

The results showed that using blood as compared with water predominantly influenced drainage flow. A 10-80% higher pressure-drop was needed to obtain same drainage flow (hematocrit of 26%) compared with manufacturer's water charts in 13-31 Fr bi-caval dual-lumen cannulae. The same net difference was found in cavo-atrial cannulae (16-32 Fr), where a lower drainage pressure was required (Hct of 26%) compared with the manufacturer's test using blood with an Hct of 33%. Return pressure-flow data were similar, independent whether pumping blood or water, to the data reported by manufacturers.

CONCLUSION

Non-standardized testing of pressure-flow properties of extracorporeal membrane oxygenation dual-lumen cannulae prevents an adequate prediction of pressure-flow results when these cannulae are used in patients. Properties of dual-lumen cannulae may vary between sizes within same cannula family, in particular concerning the drainage flow.

Pressure and flow properties of cannulae for extracorporeal membrane oxygenation II: drainage (venous) cannulae

The use of extracorporeal life support devices such as extracorporeal membrane oxygenation in adults requires cannulation of the patient's vessels with comparatively large diameter cannulae to allow circulation of large volumes of blood (>5 L/min). The cannula diameter and length are the major determinants for extracorporeal membrane oxygenation flow. Manufacturing companies present pressure-flow charts for the cannulae; however, these tests are performed with water. Aims of this study were 1. to investigate the specified pressure-flow charts obtained when using human blood as the circulating medium and 2. to support extracorporeal membrane oxygenation providers with pressure-flow data for correct choice of the cannula to reach an optimal flow with optimal hydrodynamic performance. Eighteen extracorporeal membrane oxygenation drainage cannulae, donated by the manufacturers (n = 6), were studied in a centrifugal pump driven mock loop. Pressure-flow properties and cannula features were described. The results showed that when blood with a hematocrit of 27% was used, the drainage pressure was consistently higher for a given flow (range 10%-350%) than when water was used (data from each respective manufacturer's product information). It is concluded that the information provided by manufacturers in line with regulatory guidelines does not correspond to clinical performance and therefore may not provide the best guidance for clinicians.

Hemodynamics of neonatal double lumen cannula malposition

Objective:

Malposition of dual lumen cannula is a frequent and challenging complication in neonates and plays a significant role in shaping the in vitro device hemodynamics. This study aims to analyze the effect of the dual lumen cannula malposition on right-atrial hemodynamics in neonatal patients using an experimentally validated computational fluid dynamics model.

Methods:

A computer model was developed for clinically approved dual lumen cannula (13Fr Origen Biomedical, Austin, Texas, USA) oriented inside the atrium of a 3-kg neonate with normal venous return. Atrial hemodynamics and dual lumen cannula malposition were systematically simulated for two rotations (antero-atrial and atrio-septal) and four translations (two intravascular movements along inferior vena cava and two dislodged configurations in the atrium). A multi-domain compartmentalized mesh was prepared to allow the site-specific evaluation of important hemodynamic parameters. Transport of each blood stream, blood damage levels, and recirculation times are quantified and compared to dual lumen cannula in proper position.

Results:

High recirculation levels (39 ± 4%) in malpositioned cases resulted in poor oxygen saturation where maximum recirculation of up to 42% was observed. Apparently, Origen dual lumen cannula showed poor inferior vena cava blood–capturing efficiency (48 ± 8%) but high superior vena cava blood–capturing efficiency (86 ± 10%). Dual lumen cannula malposition resulted in corresponding changes in residence time (1.7 ± 0.5 seconds through the tricuspid). No significant differences in blood damage were observed among the simulated cases compared to normal orientation. Compared to the correct dual lumen cannula position, both rotational and translational displacements of the dual lumen cannula resulted in significant hemodynamic differences.

Conclusion:

Rotational or translational movement of dual lumen cannula is the determining factor for atrial hemodynamics, venous capturing efficiency, blood residence time, and oxygenated blood delivery. Results obtained through computational fluid dynamics methodology can provide valuable foresight in assessing the performance of the dual lumen cannula in patient-specific configurations.

The Extracorporeal Life Support Organization Maastricht Treaty for Nomenclature in Extracorporeal Life Support. A Position Paper of the Extracorporeal Life Support Organization

Extracorporeal life support (ECLS) was developed more than 50 years ago, initially with venoarterial and subsequently with venovenous configurations. As the technique of ECLS significantly improved and newer skills developed, complexity in terminology and advances in cannula design led to some misunderstanding of and inconsistency in definitions, both in clinical practice and in scientific research. This document is a consensus of multispecialty international representatives of the Extracorporeal Life Support Organization, including the North America, Latin America, EuroELSO, South West Asia and Africa, and Asia-Pacific chapters, imparting a global perspective on ECLS. The goal is to provide a consistent and unambiguous nomenclature for ECLS and to overcome the inconsistent use of abbreviations for ECLS cannulation. Secondary benefits are ease of multicenter collaboration in research, improved registry data quality, and clear communication among practitioners and researchers in the field.

Differential hypoxemia during venoarterial extracorporeal membrane oxygenation

Venoarterial extracorporeal membrane oxygenation, indicated for severe cardio-respiratory failure, may result in anatomic regional differences in oxygen saturation. This depends on cannulation, hemodynamic state, and severity of respiratory failure. Differential hypoxemia, often discrete, may cause clinical problems in peripheral femoro-femoral venoarterial extracorporeal membrane oxygenation, when the upper body is perfused with low saturated blood from the heart and the lower body with well-oxygenated extracorporeal membrane oxygenation blood. The key is to diagnose and manage fulminant differential hypoxemia, that is, a state that may develop where the upper body is deprived of oxygen. We summarize physiology, assessment of diagnosis, and management of fulminant differential hypoxemia during venoarterial extracorporeal membrane oxygenation. A possible solution is implantation of an additional jugular venous return cannula. In this article, we propose an even better solution, to drain the venous blood from the superior vena cava. Drainage from the superior vena cava provides superiority to venovenoarterial configuration in terms of physiological rationale, efficiency, safety, and simplicity in clinical circuit design.

The ELSO Maastricht Treaty for ECLS Nomenclature: abbreviations for cannulation configuration in extracorporeal life support - a position paper of the Extracorporeal Life Support Organization

Background

The Extracorporeal Life Support Organization (ELSO) Maastricht Treaty for Nomenclature in Extracorporeal Life Support (ECLS) established consensus nomenclature and abbreviations for ECLS to ensure accurate, concise communication.

Methods

We build on this consensus nomenclature by layering a framework of precise and efficient abbreviations for cannula configuration that describe flow direction, number of cannulae used, any additional ECLS-related catheters, and cannulation sites. This work is a consensus of international representatives of the ELSO, including those from the North American, Latin American, European, South and West Asian, and Asian-Pacific chapters of ELSO.

Results

The classification increases in descriptive capability by introducing a third (cannula tip position) and fourth (cannula dimension) level to those provided in the previous consensus on ECLS cannulation configuration nomenclature. This expansion offers the simplest level needed to convey cannulation information yet allows for more details when required.

Conclusions

A complete nomenclature for ECLS cannulation configurations accommodating future revisions was developed to facilitate ability to compare practices and results, to promote efficient communication, and to improve quality of registry data.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2334-8) contains supplementary material, which is available to authorized users.

Impact of cannula design on packed red blood cell transfusions: technical advancement to improve outcomes in extracorporeal membrane oxygenation

Background

Technological improvement has contributed to making veno-venous extracorporeal membrane oxygenation (VV-ECMO) safer and easier, spreading its use in acute respiratory failure (ARF).

Methods

This is a retrospective observational study carried out in the ECMO center at IRCCS-ISMETT, a medical center focused on end-stage organ failure treatment in Italy. We investigated the effect of different cannula designs on the amount of blood product transfused. Eighty-nine consecutive patients affected with ARF on VV-ECMO from 2008 to 2016 were compared according to type of cannulation: older percutaneous cannula (Standard group, 52 patients) and HLS^© BIOLINE-coated, but with shorter drainage cannula (BIOLINE group, 37 patients).

Results

The two study groups were comparable in terms of baseline characteristics [age, body mass index (BMI), Simplified Acute Physiology Score (SAPS-II), Sequential Organ Failure Assessment (SOFA), Predicting Death For Severe ARDS on VV-ECMO (PRESERVE) score] and ECMO management [median hematocrit (Htc), platelet nadir, antithrombin III (AT III), heparin, activated partial thromboplastin time (APTT)]. In the BIOLINE group, a lower amount of packed red blood cells (pRBC) was transfused considering both total number [4 units, interquartile range (IQR) 1-9 vs. 12 units, IQR 5.5-21; P<0.01] and mL of pRBC/day of ECMO support (91, IQR 21-158 vs. 193.5, IQR 140.5-254; P<0.01). In the BIOLINE group, a trend in reduction of ECMO days (P=0.05) and length of intensive care unit (ICU) stay was found (P=0.06), but no differences in rates of ECMO weaning and ICU discharge were evidenced. The BIOLINE group constituted a saving of €1,295.20 per patient/treatment, counting the costs for cannulation and pRBC administration.

Conclusions

More biocompatible and shorter drainage cannula may represent one of the contributing factors to a reduction in transfusions and costs of VV-ECMO in the current ongoing technological improvement in ECMO.

Position of draining venous cannula in extracorporeal membrane oxygenation for respiratory and respiratory/circulatory support in adult patients

Extracorporeal membrane oxygenation (ECMO) is used in critically ill patients with severe pulmonary and/or cardiac failure. Blood is drained from the venous system and pumped through a membrane oxygenator where it is oxygenated. For pulmonary support, the blood is returned to the patient via a vein (veno-venous ECMO) and for pulmonary/circulatory support it is returned via an artery (veno-arterial ECMO).

Veno-venous ECMO can be performed either with a single dual-lumen cannula or with two separate single-lumen cannulas. If the latter is chosen, flow direction can either be from the inferior caval vein (IVC) to the right atrium or the opposite. Earlier research has shown that drainage from the IVC yields less recirculation and therefore the IVC to right atrium route has become the standard in most centers for veno-venous ECMO with two cannulas. However, recent research has shown that recirculation can be minimized using a multistage draining cannula in the optimal position inserted via the right internal jugular vein and with blood return to the femoral vein. The clinical results with this route are excellent.

In veno-arterial ECMO the most common site for blood infusion is the femoral artery. If venous blood is drained from the IVC, the patient is at risk of developing a dual circulation (Harlequin syndrome, North-South syndrome, differential oxygenation) meaning a poor oxygenation of the upper part of the body, while the lower part has excellent oxygenation. By instead draining from the superior caval vein (SVC) via a multistage cannula inserted in the right internal jugular vein this risk is neutralized.

In conclusion, the authors argue that draining blood from the SVC and right atrium via a multistage cannula inserted in the right internal jugular vein is equal or better than IVC drainage both in veno-venous two cannula ECMO and in veno-arterial ECMO with blood return to the femoral artery.

Use of a tracheal dilator for percutaneous insertion of 27F and 31F Avalon© dual-lumen cannulae for veno-venous extracorporeal membrane oxygenation in adults

Veno-venous extracorporeal membrane oxygenation can be performed either by two cannulae or by a single dual-lumen cannula. The dual-lumen cannulation configuration offers multiple advantages: it avoids the femoral site which may be at greater risk of infection, it improves patient mobility, eases prone positioning and greatly reduces recirculation. The Avalon was the first commercially available dual-lumen cannula for adults. It has gained much popularity, but, for more than a year now, the adult vascular access kit with the 30Fr dilator has been discontinued in the United Kingdom. In this article, we share our experience with an alternative insertion method, using a percutaneous dilatational tracheostomy kit. This off-label use of the tracheostomy dilator appears to be safe. It may allow the continuing use of Avalon dual-lumen cannulae while waiting for a more permanent solution to be provided by the manufacturer.

Cannulation for veno-venous extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is described as a modified, smaller cardiopulmonary bypass circuit. The veno-venous (VV) ECMO circuit drains venous blood, oxygenate the blood, and pump the blood back into the same venous compartment. Draining and reinfusing in the same compartment means there are a risk of recirculation. The draining position within the venous system, ECMO pump flow, return flow position within the venous system and the patients cardiac output (CO) all have an impact on recirculation. Using two single lumen cannulas or one dual lumen cannula, but also the design of the venous cannula, can have an impact on where within the venous system the cannula is draining blood and will affect the efficiency of the ECMO circuit. VV ECMO can be performed with different cannulation strategies. The use of two single lumen cannulas draining in inferior vena cava (IVC) and reinfusing in superior vena cava (SVC) or draining in SVC and reinfusing in IVC, or one dual lumen cannula inserted in right jugular vein is all possible cannulation strategies. Independent of cannulation strategy there will be a risk of recirculation. Efficiency can be reasonable in either strategy if the cannulas are carefully positioned and monitored during the dynamic procedure of pulmonary disease. The disadvantage draining from IVC only occurs when there is a need for converting from VV to veno-arterial (VA) ECMO, reinfusing in the femoral artery. Then draining from SVC is the most efficient strategy, draining low saturated venous blood, and also means low risk of dual circulation.