Calculating mixed venous saturation during veno-venous extracorporeal membrane oxygenation

Dissolved Oxygen Relevantly Contributes to Systemic Oxygenation During Venovenous Extracorporeal Membrane Oxygenation Support

When determining extracorporeal oxygen transfer (V ML O 2 ) during venovenous extracorporeal membrane oxygenation (VV ECMO) dissolved oxygen is often considered to play a subordinate role due to its poor solubility in blood plasma. This study was designed to assess the impact of dissolved oxygen on systemic oxygenation in patients with acute respiratory distress syndrome (ARDS) on VV ECMO support by differentiating between dissolved and hemoglobin-bound extracorporeal oxygen transfer. We calculated both extracorporeal oxygen transfer based on blood gas analysis using the measuring energy expenditure in extracorporeal lung support patients (MEEP) protocol and measured oxygen uptake by the native lung with indirect calorimetry. Over 20% of V ML O 2 and over 10% of overall oxygen uptake (VO 2 total ) were realized as dissolved oxygen. The transfer of dissolved oxygen mainly depended on ECMO blood flow (BF ML ). In patients with severely impaired lung function dissolved oxygen accounted for up to 28% of VO 2 total . A clinically relevant amount of oxygen is transferred as physically dissolved fraction, which therefore needs to be considered when determining membrane lung function, manage ECMO settings or guiding the weaning procedure.

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.

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.

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.

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.

Monitoring during extracorporeal membrane oxygenation

PURPOSE OF REVIEW

An increasing number of patients are placed on extracorporeal membrane oxygenation (ECMO) for respiratory or cardiac failure. Sound understanding of physiology and configuration of ECMO is essential for proper management. This review covers different monitoring parameters and tools for patients supported with different types of ECMO.

RECENT FINDINGS

Emphasis is placed on monitoring saturations at different sites depending on type of ECMO support. The main monitoring tools detailed in this review are echocardiography and pulmonary artery catheters.

SUMMARY

The review will help physicians better assess adequate ECMO support by using the appropriate parameters for each type of configuration.

An overview of medical ECMO for neonates

Extracorporeal membrane oxygenation (ECMO), a life-saving therapy for respiratory and cardiac failure, was first used in neonates in the 1970s. The indications and criteria for ECMO have changed over the years, but it continues to be an important option for those who have failed other medical therapies. Since the Extracorporeal Life Support Organization (ELSO) Registry was established in 1989, more than 29,900 neonates have been placed on ECMO for respiratory failure, with 84% surviving their ECMO course, and 73% surviving to discharge or transfer. In this chapter, we will review the basics of ECMO, patient characteristics and criteria, patient management, ECMO complications, special uses of neonatal ECMO, and patient outcomes.

Cannula Design and Recirculation During Venovenous Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation (ECMO) is used as a lifesaving rescue treatment in refractory respiratory or cardiac failure. During venovenous (VV) ECMO, the presence of recirculation is known, but quantification and actions to minimize recirculation after measurement are to date not routinely practiced. In the current study, we investigated the effect of draining cannula design on recirculation fraction (R_f) during VV ECMO; conventional mesh cannula was compared with a multistage cannula. The effect of adjusting cannula position was also studied. Recirculation was measured with ultrasound dilution technique at different ECMO flows and after cannula repositioning. All patients who were admitted to our unit between October 2014 and July 2015 catheterized by the atrio-femoral single lumen method were included. A total of 108 measurements were conducted in 14 patients. The multistage cannula showed significantly less recirculation (19.0 ± 12.2%) compared with the conventional design (38.0 ± 13.7). Pooled data in cases improved from adjustment showing reduced R_f by 7%. In conclusion, the choice of cannula matters, as does adjustment of the draining cannula position during atrio-femoral VV ECMO. By utilizing the ultrasound dilution technique to measure R_f before and after repositioning, effective ECMO flow can be improved for a more effective ECMO treatment.

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.

Management of refractory hypoxemia during venovenous extracorporeal membrane oxygenation for ARDS

Venovenous extracorporeal membrane oxygenation (VV ECMO) in acute respiratory distress syndrome (ARDS) is currently a widely used therapeutic strategy. However, patients are often still hypoxemic despite complete ECMO support. The major determinants of peripheral oxygen saturation (SpO2) during VV ECMO are pump flow, degree of recirculation, patient's systemic venous return and its oxygen saturation, hemoglobin concentration and residual lung function. Current guidelines state that the support can be considered adequate when the patient's SpO2 is equal or greater than 80%, but a possible objection could be that such a value of O2-tension may be too low and may worsen the patient's prognosis. Moving from the pathophysiology of hypoxemia during VV ECMO, this review focuses on recirculation of blood and on the possible strategies to minimize it, on the pharmacologic modulation of intrapulmonary shunt and on the questions related to management of ECMO flow and the risks and benefits of permissive hypoxemic states. Transfusional strategy during VV ECMO, administration of neuromuscular blocking agents and sedatives, therapeutic hypothermia, and prone positioning is also reviewed. The potential advantages of β-blockers are discussed. Finally, transition from VV ECMO to venoarterial ECMO (VA ECMO) or a hybrid configuration is also examined.

(13) C Breath Tests Are Feasible in Patients With Extracorporeal Membrane Oxygenation Devices

Temporary extracorporeal membrane oxygenation (ECMO) has been established as an essential part of therapy in patients with pulmonary or cardiac failure. As physiological gaseous exchange is artificially altered in this patient group, it is debatable whether a (13) C-breath test can be carried out. In this proof of technical feasibility report, we assess the viability of the (13) C-breath test LiMAx (maximum liver function capacity) in patients on ECMO therapy. All breath probes for the test device were obtained directly via the membrane oxygenator. Data of four patients receiving liver function assessment with the (13) C-breath test LiMAx while having ECMO therapy were analyzed. All results were compared with validated scenarios of the testing procedures. The LiMAx test could successfully be carried out in every case without changing ECMO settings. Clinical course of the patients ranging from multiorgan failure to no sign of liver insufficiency was in accordance with the results of the LiMAx liver function test. The (13) C-breath test is technically feasible in the context of ECMO. Further evaluation of (13) C-breath test in general would be worthwhile. The LiMAx test as a (13) C-breath test accessing liver function might be of particular predictive interest if patients with ECMO therapy develop multiorgan failure.

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

Purpose

Veno-venous ECMO is indicated in reversible life-threatening respiratory failure without life-threatening circulatory failure. Recirculation of oxygenated blood in the ECMO circuit decreases efficiency of patient oxygen delivery but is difficult to measure. We seek to identify and quantify some of the factors responsible for recirculation in a simulation model and compare with clinical data.

Methods

A closed-loop real-time simulation model of the cardiovascular system has been developed. ECMO is simulated with a fixed flow pump 0 to 5 l/min with various cannulation sites – 1) right atrium to inferior vena cava, 2) inferior vena cava to right atrium, and 3) superior+inferior vena cava to right atrium. Simulations are compared to data from a retrospective cohort of 11 consecutive adult veno-venous ECMO patients in our department.

Results

Recirculation increases with increasing ECMO-flow, decreases with increasing cardiac output, and is highly dependent on choice of cannulation sites. A more peripheral drainage site decreases recirculation substantially.

Conclusions

Simulations suggest that recirculation is a significant clinical problem in veno-venous ECMO in agreement with clinical data. Due to the difficulties in measuring recirculation and interpretation of the venous oxygen saturation in the ECMO drainage blood, flow settings and cannula positioning should rather be optimized with help of arterial oxygenation parameters. Simulation may be useful in quantification and understanding of recirculation in VV-ECMO.

Cardiac tamponade: new technology masking an old nemesis

A 16-year-old male patient underwent bilateral pulmonary embolectomy complicated by reperfusion injury and acute respiratory distress syndrome requiring venovenous extracorporeal membrane oxygenation support using a bicaval double-lumen catheter. A unique hemodynamic profile developed consistent with tamponade but without an associated decrease in venovenous extracorporeal membrane oxygenation pump flow, improved venovenous extracorporeal membrane oxygenation circuit preload, and decreased recirculation. The use of newer bicaval double-lumen catheters can result in old problems presenting in new ways and require clinicians to be ever vigilant.

[Veno-venous extracorporeal oxygenation and veno-arterial extracorporeal oxygenation. Questions, answers]

A round table, organized by the French Society of Perfusion (Sofraperf) at the French national congress on extracorporeal circulations (Perfusion 2013), was attended by perfusionists, anaesthesiologists, intensivists and surgeons around the theme of respiratory veno-venous support and veno-arterial circulatory support with extracorporeal oxygenation in intensive care units. The debate was conducted in a participatory manner by bi-directional questions-answers session between moderators and assistance. The authors report management of this type of therapy that is not perfectly homogeneous, supported on literature data. Cannulae, cannulation, circuit, oxygenator, anticoagulation, control, surveillance, weaning are subject to paragraphs with defined entry whose contents are mutually enriching.