Transpulmonary thermodilution before and during veno-venous extra-corporeal membrane oxygenation ECMO: an observational study on a potential loss of indicator into the extra-corporeal circuit

Modified Thermodilution for Simultaneous Cardiac Output and Recirculation Assessment in Veno-venous Extracorporeal Membrane Oxygenation: A Prospective Diagnostic Accuracy Study

BACKGROUND

Thermodilution is unreliable in veno-venous extracorporeal membrane oxygenation (VV-ECMO). Systemic oxygenation depends on recirculation fractions and ratios of extracorporeal membrane oxygenation (ECMO) flow to cardiac output. In a prospective in vitro simulation, this study assessed the diagnostic accuracy of a modified thermodilution technique for recirculation and cardiac output. The hypothesis was that this method provided clinically acceptable precision and accuracy for cardiac output and recirculation.

METHODS

Two ECMO circuits ran in parallel: one representing a VV-ECMO and the second representing native heart, lung, and circulation. Both circuits shared the right atrium. Extra limbs for recirculation and pulmonary shunt were added. This study simulated ECMO flows from 1 to 2.5 l/min and cardiac outputs from 2.5 to 3.5 l/min with recirculation fractions (0 to 80%) and pulmonary shunts. Thermistors in both ECMO limbs and the pulmonary artery measured the temperature changes induced by cold bolus injections into the arterial ECMO limb. Recirculation fractions were calculated from the ratio of the areas under the temperature curve (AUCs) in the ECMO limbs and from partitioning of the bolus volume (flow based). With known partitioning of bolus volumes between ECMO and pulmonary artery, cardiac output was calculated. High-precision ultrasonic flow probes served as reference for Bland-Altman plots and linear mixed-effect models.

RESULTS

Accuracy and precision for both the recirculation fraction based on AUC (bias, -5.4%; limits of agreement, -18.6 to 7.9%) and flow based (bias, -5.9%; limits of agreement, -18.8 to 7.0%) are clinically acceptable. Calculated cardiac output for all recirculation fractions was accurate but imprecise (RecirculationAUC: bias 0.56 l/min; limits of agreement, -2.27 to 3.4 l/min; and RecirculationFLOW: bias 0.48 l/min; limits of agreement, -2.22 to 3.19 l/min). Recirculation fraction increased bias and decreased precision.

CONCLUSIONS

Adapted thermodilution for VV-ECMO allows simultaneous measurement of recirculation fraction and cardiac output and may help optimize patient management with severe respiratory failure.

EDITOR’S PERSPECTIVE

Injection Site Matters: A Comparative Analysis of Transpulmonary Thermodilution via Simultaneous Femoral and Jugular Indicator Injections under Veno-Venous Extracorporeal Membrane Oxygenation Therapy

Background: The use of veno-venous extracorporeal membrane oxygenation (vv-ECMO) in acute lung failure has witnessed a notable increase. The PiCCO system is frequently used for advanced hemodynamic monitoring in this cohort. Our study aimed to investigate whether the choice of indicator injection site (jugular vs. femoral) in patients undergoing vv-ECMO therapy affects transpulmonary thermodilution (TPTD) measurements using the PiCCO® device (Pulsion Medical Systems SE, Munich, Germany). Methods: In a retrospective single-center analysis, we compared thermodilution-derived hemodynamic parameters after simultaneous jugular and femoral injections in 28 measurements obtained in two patients with respiratory failure who were undergoing vv-ECMO therapy. Results: Elevated values of the extravascular lung water index (EVLWI), intrathoracic blood volume index (ITBVI) and global end-diastolic volume index (GEDVI) were observed following femoral indicator injection compared to jugular indicator injection (EVLWI: 29.3 ± 10.9 mL/kg vs. 18.3 ± 6.71 mL/kg, p = 0.0003; ITBVI: 2163 ± 631 mL/m2 vs. 806 ± 125 mL/m2, p < 0.0001; GEDVI: 1731 ± 505 mL/m2 vs. 687 ± 141 mL/m2, p < 0.0001). The discrepancy between femoral and jugular measurements exhibited a linear correlation with extracorporeal blood flow (ECBF). Conclusions: In a PiCCO®-derived hemodynamic assessment of patients on vv-ECMO, the femoral indicator injection, as opposed to the jugular injection, resulted in an overestimation of all index parameters. This discrepancy can be attributed to mean transit time (MTt) and downslope time-dependent (DSt) variations in GEDVI and cardiac function index and is correlated with ECBF.

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.

FX06 to rescue SARS-CoV-2-induced acute respiratory distress syndrome: a randomized clinical trial

BACKGROUND

Vascular leakage is a major feature of acute respiratory distress syndrome (ARDS). We aimed to evaluate the efficacy of FX06, a drug under development that stabilizes interendothelial cell junctions, at reducing vascular leakage during SARS-CoV-2-induced ARDS.

METHODS

This multicenter, double-blinded, randomized trial included adults with COVID-19-associated ARDS who had received invasive mechanical ventilation for < 5 days and were randomized to receive either intravenous FX06 (400 mg/d, for 5 days) or its vehicle as placebo. The primary endpoint was the lowering-from day 1 to day 7-of the transpulmonary thermodilution-derived extravascular lung-water index (EVLWi).

RESULTS

Twenty-five patients were randomized to receive FX06 and 24 the placebo. Although EVLWi was elevated at baseline (median [IQR] 15.6 mL/kg [13.5; 18.5]), its declines from day 1 to day 7 were comparable for FX06 recipients and controls (respectively, - 1.9 [- 3.3; - 0.5] vs. - 0.8 [- 5.5; - 1.1] mL/kg; estimated effect - 0.8 [- 3.1; + 2.4], p = 0.51). Cardiac indexes, pulmonary vascular permeability indexes, and fluid balances were also comparable, as were PaO2/FiO2 ratios and durations of mechanical ventilation. Adverse event rates were similar for the 2 groups, although more FX06 recipients developed ventilator-associated pneumonia (16/25 (64%) vs. 6/24 (24%), p = 0.009).

CONCLUSIONS

In this unique-dosing-regimen study, FX06 did not lower SARS-CoV-2-induced pulmonary vascular leakage. Future investigations will need to evaluate its efficacy at earlier times during the disease or using other regimens. Trial registration NCT04618042. Registered 5 November 2020.

Agreement between cardiac output measurements by pulse wave analysis using the Pressure Recording Analytical Method and transthoracic echocardiography in patients with veno-venous extracorporeal membrane oxygenation therapy: An observational method comparison

BACKGROUND

Measuring cardiac output (CO) is important in patients treated with veno-venous extracorporeal membrane oxygenation (vvECMO) because vvECMO flow and CO need to be balanced. Uncalibrated pulse wave analysis with the Pressure Recording Analytical Method (PRAM) may be suitable to measure CO in patients with vvECMO therapy.

OBJECTIVE

To assess the agreement between CO measured by PRAM (PRAM-CO; test method) and CO measured by transthoracic echocardiography (TTE-CO; reference method).

DESIGN

A prospective observational method comparison study.

SETTING

The ICU of a German university hospital between March and December 2021.

PATIENTS

Thirty one adult patients with respiratory failure requiring vvECMO therapy: 29 of the 31 patients (94%) were treated for COVID-19 related respiratory failure.

MAIN OUTCOME MEASURES

PRAM-CO and TTE-CO were measured simultaneously at two time points in each patient with at least 20 min between measurements. A radial or femoral arterial catheter-derived blood pressure waveform was used for PRAM-CO measurements. TTE-CO measurements were conducted using the pulsed wave Doppler-derived velocity time integral of the left ventricular outflow tract (LVOT) and the corresponding LVOT diameter. PRAM-CO and TTE-CO were compared using Bland-Altman analysis and the percentage error (PE). We defined a PE of <30% as clinically acceptable.

RESULTS

Mean ± SD PRAM-CO was 6.86 ± 1.49 l min -1 and mean TTE-CO was 6.94 ± 1.58 l min -1 . The mean of the differences between PRAM-CO and TTE-CO was 0.09 ± 0.73 l min -1 with a lower 95% limit of agreement of -1.34 l min -1 and an upper 95% limit of agreement of 1.51 l min -1 . The PE was 21%.

CONCLUSIONS

The agreement between PRAM-CO and TTE-CO is clinically acceptable in adult patients with vvECMO therapy.

Behaviour and stability of thermodilution signals in a closed extracorporeal circuit: a bench study

Thermodilution is the gold standard for cardiac output measurement in critically ill patients. Its application in extracorporeal therapy is limited, as a portion of the thermal indicator is drawn into the extracorporeal circuit. The behaviour of thermodilution signals in extracorporeal circuits is unknown. We investigated thermodilution curves within a closed-circuit and assessed the impact of injection volume, flow and distance on the behaviour of the thermodilution signals and catheter constants. We injected 3, 5, 7 and 10 ml of thermal indicator into a heated closed circuit. Thermistors at distances of 40, 60, 80, and 100 cm from the injection port recorded the thermodilution signals (at flow settings of 0.5, 1, 1.5, and 2 L/min). Area under the curve (AUC), rise time, exponential decay and catheter constants were analysed. Linear mixed-effects models were used to evaluate the impact of circuit flow, distance and injection volume. Catheter positioning did not influence AUC (78 injections). Catheter constants were independent of flow, injection volume or distance to the injection port. The distance to the injection port increased peak temperature and rise time and decreased exponential time constant significantly. The distance to the injection port did not influence catheter constants, but the properties of the thermodilution signal itself. This may influence measurements that depend on the exponential decay of the thermodilution signal such as right ventricular ejection fraction.

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.

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

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

Radiographic assessment of lung edema (RALE) score is associated with clinical outcomes in patients with refractory cardiogenic shock and refractory cardiac arrest after percutaneous implantation of extracorporeal life support

VA-ECMO is a promising therapeutic option in refractory cardiogenic shock (RCS) and refractory cardiac arrest (RCA). However, increase in left ventricular afterload enhances further reduction of LV contractility and pulmonary edema. The aim of this study was to evaluate pulmonary edema based on the RALE score and the prognostic value of the score on ECLS weaning and mortality. In this retrospective study, data from 40 patients (16 RCAs and 24 RCSs) were analyzed. Demographic, clinical data and the RALE score for evaluating pulmonary edema were assessed. Descriptive statistics, intraclass correlation, and receiver operating characteristic (ROC) curves were computed. Weaning from ECLS was successful in 30 (75%) patients, 16 patients (40%) were discharged alive. Overall, the survivors were younger, presenting with a higher left ventricular ejection fraction (30 ± 2% vs.23 ± 9%;p < 0.01) and a lower initial serum lactate concentration 7.7 ± 4.5 mmol/l vs. 11.5 ± 4.9 mmol/l; p = 0.017). Survivors had lower RALE scores than non-survivors (16.3 ± 9.4 vs. 26.4 ± 10.4; p = 0.0034). The interobserver variability of the RALE score was good (0.832). The AUC predicting mortality and weaning from ECLS presented comparable results to the established parameters (SAVE, serum lactate). Implementation of the RALE score could support prediction of outcome parameters during VA-ECMO therapy.

Veno-Venous Extracorporeal Membrane Oxygenation in Minipigs as a Robust Tool to Model Acute Kidney Injury: Technical Notes and Characteristics

Objective

Veno-venous extracorporeal membrane oxygenation (vv-ECMO) can save lives in severe respiratory distress, but this innovative approach has serious side-effects and is accompanied by higher rates of iatrogenic morbidity. Our aims were, first, to establish a large animal model of vv-ECMO to study the pathomechanism of complications within a clinically relevant time frame and, second, to investigate renal reactions to increase the likelihood of identifying novel targets and to improve clinical outcomes of vv-ECMO-induced acute kidney injury (AKI).

Methods

Anesthetized Vietnamese miniature pigs were used. After cannulation of the right jugular and femoral veins, vv-ECMO was started and maintained for 24 hrs. In Group 1 (n = 6) ECMO was followed by a further 6-hr post-ECMO period, while (n = 6) cannulation was performed without ECMO in the control group, with observation maintained for 30 h. Systemic hemodynamics, blood gas values and hour diuresis were monitored. Renal artery flow (RAF) was measured in the post-ECMO period with an ultrasonic flowmeter. At the end of the experiments, renal tissue samples were taken for histology to measure myeloperoxidase (MPO) and xanthine oxidoreductase (XOR) activity and to examine mitochondrial function with high-resolution respirometry (HRR, Oroboros, Austria). Plasma and urine samples were collected every 6 hrs to determine neutrophil gelatinase-associated lipocalin (NGAL) concentrations.

Results

During the post-ECMO period, RAF dropped (96.3 ± 21 vs. 223.6 ± 32 ml/min) and, similarly, hour diuresis was significantly lower as compared to the control group (3.25 ± 0.4 ml/h/kg vs. 4.83 ± 0.6 ml/h/kg). Renal histology demonstrated significant structural damage characteristic of ischemic injury in the tubular system. In the vv-ECMO group NGAL levels, rose significantly in both urine (4.24 ± 0.25 vs. 2.57 ± 0.26 ng/ml) and plasma samples (4.67 ± 0.1 vs. 3.22 ± 0.2 ng/ml), while tissue XOR (5.88 ± 0.8 vs. 2.57 ± 0.2 pmol/min/mg protein) and MPO (11.93 ± 2.5 vs. 4.34 ± 0.6 mU/mg protein) activity was elevated. HRR showed renal mitochondrial dysfunction, including a significant drop in complex-I-dependent oxidative capacity (174.93 ± 12.7 vs. 249 ± 30.07 pmol/s/ml).

Conclusion

Significantly decreased renal function with signs of structural damage and impaired mitochondrial function developed in the vv-ECMO group. The vv-ECMO-induced acute renal impairment in this 30-hr research protocol provides a good basis to study the pathomechanism, biomarker combinations or possible therapeutic possibilities for AKI.

CRRT influences PICCO measurements in febrile critically ill patients

The aim of this study was to investigate whether continuous renal replacement therapy (CRRT) influences the global end-diastolic volume index (GEDVI), cardiac index (CI), and extravascular lung water index (EVLWI) measured by Pulse Index Continuous Cardiac Output (PICCO) in febrile patients. Fifteen fever patients were included in this study. CI, GEDVI, EVLWI, heart rate (HR), and mean arterial pressure (MAP) were measured at five time-points: before CRRT (T0), immediately after CRRT started (T1), 15 min after CRRT started (T2), immediately after CRRT stopped (T3), and 15 min after CRRT stopped (T4). Results have shown that CI and GEDVI were decreased significantly in T1 (CI: 4.09 ± 0.72 vs 2.81 ± 0.58 L/min m², P = 0.000 and GEDVI: 727.86 ± 63.47 vs 531.07 ± 66.63 mL/m², P = 0.000). However, CI and GEDVI were significantly increased in T3 (CI: 4.09 ± 0.72 vs 7.23 ± 1.32 L/min m², P = 0.000 and GEDVI 727.86 ± 63.47 vs 1339.17 ± 121.52 mL/m², P = 0.000). There were no significant differences in T2 and T4. Among the five-time points, no measurement errors were observed with regards to HR, MAP, and EVLWI. Therefore, the data herein contained suggests that PICCO measurements should begin 15 min after the start or stop of CRRT.

Safety and preliminary efficacy of sequential multiple ascending doses of solnatide to treat pulmonary permeability edema in patients with moderate-to-severe ARDS-a randomized, placebo-controlled, double-blind trial

Background

Acute respiratory distress syndrome (ARDS) is a complex clinical diagnosis with various possible etiologies. One common feature, however, is pulmonary permeability edema, which leads to an increased alveolar diffusion pathway and, subsequently, impaired oxygenation and decarboxylation. A novel inhaled peptide agent (AP301, solnatide) was shown to markedly reduce pulmonary edema in animal models of ARDS and to be safe to administer to healthy humans in a Phase I clinical trial. Here, we present the protocol for a Phase IIB clinical trial investigating the safety and possible future efficacy endpoints in ARDS patients.

Methods

This is a randomized, placebo-controlled, double-blind intervention study. Patients with moderate to severe ARDS in need of mechanical ventilation will be randomized to parallel groups receiving escalating doses of solnatide or placebo, respectively. Before advancing to a higher dose, a data safety monitoring board will investigate the data from previous patients for any indication of patient safety violations. The intervention (application of the investigational drug) takes places twice daily over the course of 7 days, ensued by a follow-up period of another 21 days.

Discussion

The patients to be included in this trial will be severely sick and in need of mechanical ventilation. The amount of data to be collected upon screening and during the course of the intervention phase is substantial and the potential timeframe for inclusion of any given patient is short. However, when prepared properly, adherence to this protocol will make for the acquisition of reliable data. Particular diligence needs to be exercised with respect to informed consent, because eligible patients will most likely be comatose and/or deeply sedated at the time of inclusion.

Trial registration

This trial was prospectively registered with the EU Clinical trials register (clinicaltrialsregister.eu). EudraCT Number: 2017-003855-47.

Convalescent plasma therapy in B-cell-depleted and B-cell sufficient patients with life-threatening COVID-19 - A case series

Objective

To investigate the effect of convalescent plasma therapy (CPT) on clinical courses of B-cell-sufficient and B-cell-depleted patients with life-threatening COVID-19.

Patients and Methods

In this case series, we retrospectively analysed clinical, laboratory and cardiopulmonary parameters of six patients with life-threatening COVID-19 receiving convalescent plasma (CP) as rescue therapy between April 11, 2020 to October 10, 2020. Clinical and laboratory parameters before and after transfusion were compared in two B-cell-depleted patients and four B-cell sufficient patients (control group).

Results

Both B-cell-depleted patients cleared SARS-CoV-2 virus and survived, while all other patients died within 14 days from intervention despite maximal therapeutic efforts. D-dimer levels increased in both cohorts subsequent to CPT. In control patients, mean Interleukin-6 increased and platelet levels decreased as opposed to decreasing and stable levels in B-cell-depleted patients, respectively. Control patients required increased doses of vasopressor compared to decreasing doses in B-cell depleted patients subsequent to CPT. PO₂/FiO₂ decrease was more pronounced and respiratory deterioration required postinterventional extracorporeal membrane oxygenation in two control patients. Transpulmonary thermodilution revealed a further increase of the Extravascular Lung Water Index upon CPT in control patients.

Conclusion

Use of CP in late stages of life-threatening COVID-19 should be used with caution but may be beneficial in B-cell-depleted patients. Further studies are necessary to assess factors predicting potential therapeutic benefits as well as possible hazards.

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.

Increased extravascular lung water index (EVLWI) reflects rapid non-cardiogenic oedema and mortality in COVID-19 associated ARDS

Nearly 5% of patients suffering from COVID-19 develop acute respiratory distress syndrome (ARDS). Extravascular lung water index (EVLWI) is a marker of pulmonary oedema which is associated with mortality in ARDS. In this study, we evaluate whether EVLWI is higher in patients with COVID-19 associated ARDS as compared to COVID-19 negative, ventilated patients with ARDS and whether EVLWI has the potential to monitor disease progression. EVLWI and cardiac function were monitored by transpulmonary thermodilution in 25 patients with COVID-19 ARDS subsequent to intubation and compared to a control group of 49 non-COVID-19 ARDS patients. At intubation, EVLWI was noticeably elevated and significantly higher in COVID-19 patients than in the control group (17 (11–38) vs. 11 (6–26) mL/kg; p < 0.001). High pulmonary vascular permeability index values (2.9 (1.0–5.2) versus 1.9 (1.0–5.2); p = 0.003) suggested a non-cardiogenic pulmonary oedema. By contrast, the cardiac parameters SVI, GEF and GEDVI were comparable in both cohorts. High EVLWI values were associated with viral persistence, prolonged intensive care treatment and in-hospital mortality (23.2 ± 6.7% vs. 30.3 ± 6.0%, p = 0.025). Also, EVLWI showed a significant between-subjects (r = − 0.60; p = 0.001) and within-subjects correlation (r = − 0.27; p = 0.028) to Horowitz index. Compared to non COVID-19 ARDS, COVID-19 results in markedly elevated EVLWI-values in patients with ARDS. High EVLWI reflects a non-cardiogenic pulmonary oedema in COVID-19 ARDS and could serve as parameter to monitor ARDS progression on ICU.

Assessment of Right Heart Function during Extracorporeal Therapy by Modified Thermodilution in a Porcine Model

BACKGROUND

Veno-arterial extracorporeal membrane oxygenation therapy is a growing treatment modality for acute cardiorespiratory failure. Cardiac output monitoring during veno-arterial extracorporeal membrane oxygenation therapy remains challenging. This study aims to validate a new thermodilution technique during veno-arterial extracorporeal membrane oxygenation therapy using a pig model.

METHODS

Sixteen healthy pigs were centrally cannulated for veno-arterial extracorporeal membrane oxygenation, and precision flow probes for blood flow assessment were placed on the pulmonary artery. After chest closure, cold boluses of 0.9% saline solution were injected into the extracorporeal membrane oxygenation circuit, right atrium, and right ventricle at different extracorporeal membrane oxygenation flows (4, 3, 2, 1 l/min). Rapid response thermistors in the extracorporeal membrane oxygenation circuit and pulmonary artery recorded the temperature change. After calculating catheter constants, the distributions of injection volumes passing each circuit were assessed and enabled calculation of pulmonary blood flow. Analysis of the exponential temperature decay allowed assessment of right ventricular function.

RESULTS

Calculated blood flow correlated well with measured blood flow (r2 = 0.74, P < 0.001). Bias was -6 ml/min [95% CI ± 48 ml/min] with clinically acceptable limits of agreement (668 ml/min [95% CI ± 166 ml/min]). Percentage error varied with extracorporeal membrane oxygenation blood flow reductions, yielding an overall percentage error of 32.1% and a percentage error of 24.3% at low extracorporeal membrane oxygenation blood flows. Right ventricular ejection fraction was 17 [14 to 20.0]%. Extracorporeal membrane oxygenation flow reductions increased end-diastolic and end-systolic volumes with reductions in pulmonary vascular resistance. Central venous pressure and right ventricular ejection fractions remained unchanged. End-diastolic and end-systolic volumes correlated highly (r2 = 0.98, P < 0.001).

CONCLUSIONS

Adapted thermodilution allows reliable assessment of cardiac output and right ventricular behavior. During veno-arterial extracorporeal membrane oxygenation weaning, the right ventricle dilates even with stable function, possibly because of increased venous return.

EDITOR’S PERSPECTIVE

Lower blood return temperature than core temperature as a causal factor of decreased cardiac output assessed by transpulmonary thermodilution during blood purification

We aimed to evaluate whether cardiac output assessed by transpulmonary thermodilution during blood purification is affected by the difference between the blood return temperature and core temperature. We applied different blood return temperatures using a thermostat bath during blood purification in four pigs. After the blood return temperature stabilized and blood purification process stopped, the cardiac output assessed by transpulmonary thermodilution was measured. The thermostat bath was set at 35°C, 40°C, 45°C, and 50°C, with the order changed at random; four measurements were made at each temperature. Cardiac function was evaluated by echocardiography when ice-cold saline was administered in a pig. A decrease in the blood return temperature resulted in decreased cardiac output assessed by transpulmonary thermodilution, whereas an increase resulted in increased cardiac output assessed by transpulmonary thermodilution. Echocardiography revealed that the change in the blood return temperature did not affect the left ventricular ejection fraction.

Options in extracorporeal support of multiple organ failure

Multiorgan failure is among the most frequent reasons of death in critically ill patients. Based on extensive and long-term use of renal replacement therapy, extracorporeal organ support became available for other organ failures. Initially, most of these techniques (e.g. extracorporeal membrane oxygenation, extracorporeal CO₂ removal [ECCO2R] and extracorporeal liver support) were used as stand-alone single organ support systems. Considering multiple interactions between native organs (“crosstalk”), combined or integrated extracorporeal organ support (ECOS) devices are intriguing. The concept of multiple organ support therapy (MOST) providing simultaneous and combined support for different failing organs was described more than 15 years ago by Ronco and Bellomo. This concept also implicates overcoming the “compartmentalized” approach provided by different single organ specialized professionals by a multidisciplinary and multiprofessional strategy. The idea of MOST is supported by the failure of several recent studies on single organ support including liver and lung support. Improvement of outcome by ECOS necessarily depends on optimized patient selection, integrated organ support and limitation of its side effects. This implicates challenges for engineers, industry and healthcare professionals. From a technical viewpoint, modular combination of pre-existing technologies such as renal replacement, albumin-dialysis, ECCO2R and potentially cytokine elimination can be considered as a first step. While this allows for stepwise and individual combination of standard organ support facilities, it carries the disadvantage of large extracorporeal blood volume and surfaces as well as additive costs. The more intriguing next step is an integrated platform providing the capacity of multiple organ support within one device. (This article is freely available.)