In-vitro performance of a low flow extracorporeal carbon dioxide removal circuit

State of the art: Monitoring of the respiratory system during veno-venous extracorporeal membrane oxygenation

Monitoring the patient receiving veno-venous extracorporeal membrane oxygenation (VV ECMO) is challenging due to the complex physiological interplay between native and membrane lung. Understanding these interactions is essential to understand the utility and limitations of different approaches to respiratory monitoring during ECMO. We present a summary of the underlying physiology of native and membrane lung gas exchange and describe different tools for titrating and monitoring gas exchange during ECMO. However, the most important role of VV ECMO in severe respiratory failure is as a means of avoiding further ergotrauma. Although optimal respiratory management during ECMO has not been defined, over the last decade there have been advances in multimodal respiratory assessment which have the potential to guide care. We describe a combination of imaging, ventilator-derived or invasive lung mechanic assessments as a means to individualise management during ECMO.

Extracorporeal Carbon Dioxide Removal With the Hemolung in Patients With Acute Respiratory Failure: A Multicenter Retrospective Cohort Study

OBJECTIVES

Extracorporeal carbon dioxide removal (ECCO 2 R) devices are effective in reducing hypercapnia and mechanical ventilation support but have not been shown to reduce mortality. This may be due to case selection, device performance, familiarity, or the management. The objective of this study is to investigate the effectiveness and safety of a single ECCO 2 R device (Hemolung) in patients with acute respiratory failure and identify variables associated with survival that could help case selection in clinical practice as well as future research.

DESIGN

Multicenter, multinational, retrospective review.

SETTING

Data from the Hemolung Registry between April 2013 and June 2021, where 57 ICUs contributed deidentified data.

PATIENTS

Patients with acute respiratory failure treated with the Hemolung. The characteristics of patients who survived to ICU discharge were compared with those who died. Multivariable logistical regression analysis was used to identify variables associated with ICU survival.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Of the 159 patients included, 65 (41%) survived to ICU discharge. The survival was highest in status asthmaticus (86%), followed by acute respiratory distress syndrome (ARDS) (52%) and COVID-19 ARDS (31%). All patients had a significant reduction in Pa co2 and improvement in pH with reduction in mechanical ventilation support. Patients who died were older, had a lower Pa o2 :F io2 (P/F) and higher use of adjunctive therapies. There was no difference in the complications between patients who survived to those who died. Multivariable regression analysis showed non-COVID-19 ARDS, age less than 65 years, and P/F at initiation of ECCO 2 R to be independently associated with survival to ICU discharge (P/F 100-200 vs <100: odds ratio, 6.57; 95% CI, 2.03-21.33).

CONCLUSIONS

Significant improvement in hypercapnic acidosis along with reduction in ventilation supports was noted within 4 hours of initiating ECCO 2 R. Non-COVID-19 ARDS, age, and P/F at commencement of ECCO 2 R were independently associated with survival.

A randomised controlled trial of non-invasive ventilation compared with extracorporeal carbon dioxide removal for acute hypercapnic exacerbations of chronic obstructive pulmonary disease

Background

Patients presenting with acute hypercapnic respiratory failure due to exacerbations of chronic obstructive pulmonary disease (AECOPD) are typically managed with non-invasive ventilation (NIV). The impact of low-flow extracorporeal carbon dioxide removal (ECCO₂R) on outcome in these patients has not been explored in randomised trials.

Methods

Open-label randomised trial comparing NIV (NIV arm) with ECCO₂R (ECCO₂R arm) in patients with AECOPD at high risk of NIV failure (pH < 7.30 after ≥ 1 h of NIV). The primary endpoint was time to cessation of NIV. Secondary outcomes included device tolerance and complications, changes in arterial blood gases, hospital survival.

Results

Eighteen patients (median age 67.5, IQR (61.5–71) years; median GOLD stage 3 were enrolled (nine in each arm). Time to NIV discontinuation was shorter with ECCO₂R (7:00 (6:18–8:30) vs 24:30 (18:15–49:45) h, p = 0.004). Arterial pH was higher with ECCO₂R at 4 h post-randomisation (7.35 (7.31–7.37) vs 7.25 (7.21–7.26), p < 0.001). Partial pressure of arterial CO₂ (PaCO₂) was significantly lower with ECCO₂R at 4 h (6.8 (6.2–7.15) vs 8.3 (7.74–9.3) kPa; p = 0.024). Dyspnoea and comfort both rapidly improved with commencement of ECCO₂R. There were no severe or life-threatening complications in the study population. There were no episodes of major bleeding or red blood cell transfusion in either group. ICU and hospital length of stay were longer with ECCO₂R, and there was no difference in 90-day mortality or functional outcomes at follow-up.

Interpretation

There is evidence of benefit associated with ECCO₂R with time to improvement in respiratory acidosis, in respiratory physiology and an immediate improvement in patient comfort and dyspnoea with commencement of ECCO₂R. In addition, there was minimal clinically significant adverse events associated with ECCO₂R use in patients with AECOPD at risk of failing or not tolerating NIV. However, the ICU and hospital lengths of stay were longer in the ECCO₂R for similar outcomes.

Trial registration The trial is prospectively registered on ClinicalTrials.gov: NCT02086084. Registered on 13th March 2014, https://clinicaltrials.gov/ct2/show/NCT02086084?cond=ecco2r&draw=2&rank=8

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-022-01006-8.

Estimating cardiac output based on gas exchange during veno-arterial extracorporeal membrane oxygenation in a simulation study using paediatric oxygenators

Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) therapy is a rescue strategy for severe cardiopulmonary failure. The estimation of cardiac output during VA-ECMO is challenging. 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CO₂ or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V.O_2Lung)/(\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V.CO₂ or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V.O_2ECMO). A normalization procedure corrected \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V.CO₂ values for a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V./\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{Q}}}$$\end{document}Q˙ of 1. Method agreement was evaluated by Bland–Altman analysis. Calculated \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{Q}}}$$\end{document}Q˙_Lung using gaseous \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V.CO₂ and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V.O₂ correlated well with measured \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{Q}}}$$\end{document}Q˙_Lung with a bias of 103 ml/min [− 268 to 185] ml/min; Limits of Agreement: − 306 ml/min [− 241 to − 877 ml/min] to 512 ml/min [447 to 610 ml/min], r² 0.85 [0.79–0.88]). Blood measurements of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V.CO₂ showed an increased bias (− 260 ml/min [− 1503 to 982] ml/min), clinically not applicable. Shunt and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V./\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{Q}}}$$\end{document}Q˙ mismatch decreased the agreement of methods significantly. This in-vitro simulation shows that \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V.CO₂ and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathop {\text{V}}\limits^{.}$$\end{document}V.O₂ in steady-state conditions allow for clinically applicable calculations of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{Q}}}$$\end{document}Q˙_Lung during VA-ECMO therapy.

Comparison of Circular and Parallel-Plated Membrane Lungs for Extracorporeal Carbon Dioxide Elimination

Extracorporeal carbon dioxide removal (ECCO₂R) is an important technique to treat critical lung diseases such as exacerbated chronic obstructive pulmonary disease (COPD) and mild or moderate acute respiratory distress syndrome (ARDS). This study applies our previously presented ECCO₂R mock circuit to compare the CO₂ removal capacity of circular versus parallel-plated membrane lungs at different sweep gas flow rates (0.5, 2, 4, 6 L/min) and blood flow rates (0.3 L/min, 0.9 L/min). For both designs, two low-flow polypropylene membrane lungs (Medos Hilte 1000, Quadrox-i Neonatal) and two mid-flow polymethylpentene membrane lungs (Novalung Minilung, Quadrox-iD Pediatric) were compared. While the parallel-plated Quadrox-iD Pediatric achieved the overall highest CO₂ removal rates under medium and high sweep gas flow rates, the two circular membrane lungs performed relatively better at the lowest gas flow rate of 0.5 L/min. The low-flow Hilite 1000, although overall better than the Quadrox i-Neonatal, had the most significant advantage at a gas flow of 0.5 L/min. Moreover, the circular Minilung, despite being significantly less efficient than the Quadrox-iD Pediatric at medium and high sweep gas flow rates, did not show a significantly worse CO₂ removal rate at a gas flow of 0.5 L/min but rather a slight advantage. We suggest that circular membrane lungs have an advantage at low sweep gas flow rates due to reduced shunting as a result of their fiber orientation. Efficiency for such low gas flow scenarios might be relevant for possible future portable ECCO₂R devices.

Suitable CO2 Solubility Models for Determination of the CO2 Removal Performance of Oxygenators

CO₂ removal via membrane oxygenators during lung protective ventilation has become a reliable clinical technique. For further optimization of oxygenators, accurate prediction of the CO₂ removal rate is necessary. It can either be determined by measuring the CO₂ content in the exhaust gas of the oxygenator (sweep flow-based) or using blood gas analyzer data and a CO₂ solubility model (blood-based). In this study, we determined the CO₂ removal rate of a prototype oxygenator utilizing both methods in in vitro trials with bovine and in vivo trials with porcine blood. While the sweep flow-based method is reliably accurate, the blood-based method depends on the accuracy of the solubility model. In this work, we quantified performances of four different solubility models by calculating the deviation of the CO₂ removal rates determined by both methods. Obtained data suggest that the simplest model (Loeppky) performs better than the more complex ones (May, Siggaard-Anderson, and Zierenberg). The models of May, Siggaard-Anderson, and Zierenberg show a significantly better performance for in vitro bovine blood data than for in vivo porcine blood data. Furthermore, the suitability of the Loeppky model parameters for bovine blood (in vitro) and porcine blood (in vivo) is evaluated.

A mock circulation loop to test extracorporeal CO2 elimination setups

Background

Extracorporeal carbon dioxide removal (ECCO₂R) is a promising yet limited researched therapy for hypercapnic respiratory failure in acute respiratory distress syndrome and exacerbated chronic obstructive pulmonary disease. Herein, we describe a new mock circuit that enables experimental ECCO₂R research without animal models. In a second step, we use this model to investigate three experimental scenarios of ECCO₂R: (I) the influence of hemoglobin concentration on CO₂ removal. (II) a potentially portable ECCO₂R that uses air instead of oxygen, (III) a low-flow ECCO₂R that achieves effective CO₂ clearance by recirculation and acidification of the limited blood volume of a small dual lumen cannula (such as a dialysis catheter).

Results

With the presented ECCO₂R mock, CO₂ removal rates comparable to previous studies were obtained. The mock works with either fresh porcine blood or diluted expired human packed red blood cells. However, fresh porcine blood was preferred because of better handling and availability. In the second step of this work, hemoglobin concentration was identified as an important factor for CO₂ removal. In the second scenario, an air-driven ECCO₂R setup showed only a slightly lower CO₂ wash-out than the same setup with pure oxygen as sweep gas. In the last scenario, the low-flow ECCO₂R, the blood flow at the test membrane lung was successfully raised with a recirculation channel without the need to increase cannula flow. Low recirculation ratios resulted in increased efficiency, while high recirculation ratios caused slightly reduced CO₂ removal rates. Acidification of the CO₂ depleted blood in the recirculation channel caused an increase in CO₂ removal rate.

Conclusions

We demonstrate a simple and cost effective, yet powerful, “in-vitro” ECCO₂R model that can be used as an alternative to animal experiments for many research scenarios. Moreover, in our approach parameters such as hemoglobin level can be modified more easily than in animal models.

Update on extracorporeal carbon dioxide removal: a comprehensive review on principles, indications, efficiency, and complications

TECHNOLOGY

Extracorporeal carbon dioxide removal means the removal of carbon dioxide from the blood across a gas exchange membrane without substantially improving oxygenation. Carbon dioxide removal is possible with substantially less extracorporeal blood flow than needed for oxygenation. Techniques for extracorporeal carbon dioxide removal include (1) pumpless arterio-venous circuits, (2) low-flow venovenous circuits based on the technology of continuous renal replacement therapy, and (3) venovenous circuits based on extracorporeal membrane oxygenation technology.

INDICATIONS

Extracorporeal carbon dioxide removal has been shown to enable more protective ventilation in acute respiratory distress syndrome patients, even beyond the so-called "protective" level. Although experimental data suggest a benefit on ventilator induced lung injury, no hard clinical evidence with respect to improved outcome exists. In addition, extracorporeal carbon dioxide removal is a tool to avoid intubation and mechanical ventilation in patients with acute exacerbated chronic obstructive pulmonary disease failing non-invasive ventilation. This concept has been shown to be effective in 56-90% of patients. Extracorporeal carbon dioxide removal has also been used in ventilated patients with hypercapnic respiratory failure to correct acidosis, unload respiratory muscle burden, and facilitate weaning. In patients suffering from terminal fibrosis awaiting lung transplantation, extracorporeal carbon dioxide removal is able to correct acidosis and enable spontaneous breathing during bridging. Keeping these patients awake, ambulatory, and breathing spontaneously is associated with favorable outcome.

COMPLICATIONS

Complications of extracorporeal carbon dioxide removal are mostly associated with vascular access and deranged hemostasis leading to bleeding. Although the spectrum of complications may differ, no technology offers advantages with respect to rate and severity of complications. So called "high-extraction systems" working with higher blood flows and larger membranes may be more effective with respect to clinical goals.