Blood oxygenation and decarboxylation determinants during venovenous ECMO for respiratory failure in adults

Electroencephalographic features in patients undergoing extracorporeal membrane oxygenation

Background

Neurologic injury is one of the most frequent causes of death in patients undergoing extracorporeal membrane oxygenation (ECMO). As neurological examination is often unreliable in sedated patients, additional neuromonitoring is needed. However, the value of electroencephalogram (EEG) in adult ECMO patients has not been well assessed. Therefore, the aim of this study was to assess the occurrence of electroencephalographic abnormalities in patients treated with extracorporeal membrane oxygenation (ECMO) and their association with 3-month neurologic outcome.

Methods

Retrospective analysis of all patients undergoing venous–venous (V–V) or venous–arterial (V–A) ECMO with a concomitant EEG recording (April 2009–December 2018), either recorded intermittently or continuously. EEG background was classified into four categories: mild/moderate encephalopathy (i.e., mostly defined by the presence of reactivity), severe encephalopathy (mostly defined by the absence of reactivity), burst-suppression (BS) and suppressed background. Epileptiform activity (i.e., ictal EEG pattern, sporadic epileptiform discharges or periodic discharges) and asymmetry were also reported. EEG findings were analyzed according to unfavorable neurological outcome (UO, defined as Glasgow Outcome Scale < 4) at 3 months after discharge.

Results

A total of 139 patients (54 [41–62] years; 60 (43%) male gender) out of 596 met the inclusion criteria and were analyzed. Veno–arterial (V–A) ECMO was used in 98 (71%); UO occurred in 99 (71%) patients. Continuous EEG was performed in 113 (81%) patients. The analysis of EEG background showed that 29 (21%) patients had severe encephalopathy, 4 (3%) had BS and 19 (14%) a suppressed background. In addition, 11 (8%) of patients had seizures or status epilepticus, 10 (7%) had generalized periodic discharges or lateralized periodic discharges, and 27 (19%) had asymmetry on EEG. In the multivariate analysis, the occurrence of ischemic stroke or intracranial hemorrhage (OR 4.57 [1.25–16.74]; p = 0.02) and a suppressed background (OR 10.08 [1.24–82.20]; p = 0.03) were independently associated with UO. After an adjustment for covariates, an increasing probability for UO was observed with more severe EEG background categories.

Conclusions

In adult patients treated with ECMO, EEG can identify patients with a high likelihood of poor outcome. In particular, suppressed background was independently associated with unfavorable neurological outcome.

Diaphragm Thickening During Venoarterial Extracorporeal Membrane Oxygenation Weaning: An Observational Prospective Study

OBJECTIVES

The respiratory workload, according to the diaphragm thickening fraction (TF) during sweep gas flow (SGF), decrease during weaning from venoarterial extracorporeal membrane oxygenation (VA ECMO) was evaluated for the present study.

DESIGN

Prospective observational study.

SETTING

Monocentric.

PARTICIPANTS

Patients were included if they were suitable for a first VA ECMO weaning trial and were breathing spontaneously.

INTERVENTIONS

SGF was set for 15 minutes when the TF was measured at 4 L/min, 2 L/min, and 1 L/min, with a 10-minute return to baseline between each step. Mechanical ventilation, when required, was set to pressure-support ventilation mode with 7 cmH₂O (pressure support) and a positive end-expiratory pressure of 0 cmH₂O. Diaphragm ultrasound was used to assess the TF at the end of each step. Demographics, left ventricular ejection fraction (LVEF), and outcome were collected.

MEASUREMENTS AND MAIN RESULTS

Fifteen patients were included. Ten patients were extubated, and five were ventilated. TF values were 6.3% [0-10] at 4 L/min, 13.3% [10-26] at 2 L/min, and 26.7% [22-44] at 1 L/min (analysis of variance: p < 0.001 between 4 L/min and 2 L/min and p = 0.03 between 2 L/min and 1 L/min). TF did not differ whether patients were or were not ventilated or whether they were or were not weaned successfully from ECMO. TF was correlated with LVEF at 1 L/min SGF (Pearson R 0.67 [0.21-0.88]; p = 0.009) and at 2 L/min (R 0.7 [0.27-0.89]; p = 0.005) but not at 4 L/min. SGF mitigated the relationship between LVEF and TF (analysis of covariance: p < 0.005).

CONCLUSIONS

Diaphragm TF was related to the SGF of the venoarterial ECMO settings and LVEF at the time of weaning.

Pathophysiology of respiratory failure and physiology of gas exchange during ECMO

Lungs play a key role in sustaining cellular respiration by regulating the levels of oxygen and carbon dioxide in the blood. This is achieved by exchanging these gases between blood and ambient air across the alveolar capillary membrane by the process of diffusion. In the microstructure of the lung, gas exchange is compartmentalized and happens in millions of microscopic alveolar units. In situations of lung injury, this structural complexity is disrupted resulting in impaired gas exchange. Depending on the severity and the type of lung injury, different aspects of pulmonary physiology are affected. If the respiratory failure is refractory to ventilator support, extracorporeal membrane oxygenation (ECMO) can be utilized to support the gas exchange needs of the body. In ECMO, thin hollow fiber membranes made up of polymethylpentene act as blood-gas interface for diffusion. Decades of innovative engineering with membranes and their alignment with blood and gas flows has enabled modern oxygenators to achieve clinically and physiologically significant amount of gas exchange.

[COVID-19 and mechanical circulatory support]

La principale indication d’assistance chez les patients COVID-19 est le SDRA sévère en échec de traitement conventionnel. Les résultats de l’ECMO veino-veineuse sont comparables dans le COVID-19 à ceux obtenus dans les SDRA d’autres origines. La gestion de l’ECMO durant la pandémie COVID-19 a des spécificités liées à la maladie (comme par exemple la gestion de l’anticoagulation) et à l’allocation des ressources. Plus rarement, la COVID-19 peut se compliquer de défaillance hémodynamique dans le cadre d’une myocardite fulminante ou d’une embolie pulmonaire massive et nécessiter alors la mise en place d’une ECMO veino-artérielle. Bien que les cas rapportés soient peu nombreux, l’assistance circulatoire peut permettre une évolution favorable dans ces 2 indications.

Extracorporeal membrane oxygenation for COVID-19 induced hypoxia: Single-center study

INTRODUCTION

The pandemic of the coronavirus disease 2019 (COVID-19) and associated pneumonia represent a clinical and scientific challenge. The role of Extracorporeal Membrane Oxygenation (ECMO) in such a crisis remains unclear.

METHODS

We examined COVID-19 patients who were supported for acute respiratory failure by both conventional mechanical ventilation (MV) and ECMO at a tertiary care institution in Washington DC. The study period extended from March 23 to April 29. We identified 59 patients who required invasive mechanical ventilation. Of those, 13 patients required ECMO.

RESULTS

Nine out of 13 ECMO (69.2%) patients were decannulated from ECMO. All-cause ICU mortality was comparable between both ECMO and MV groups (6 patients [46.15%] vs. 22 patients [47.82 %], p = 0.92). ECMO non-survivors vs survivors had elevated D-dimer (9.740 mcg/ml [4.84-20.00] vs. 3.800 mcg/ml [2.19-9.11], p = 0.05), LDH (1158 ± 344.5 units/L vs. 575.9 ± 124.0 units/L, p = 0.001), and troponin (0.4315 ± 0.465 ng/ml vs. 0.034 ± 0.043 ng/ml, p = 0.04). Time on MV as expected was significantly longer in ECMO groups (563.3 hours [422.1-613.9] vs. 247.9 hours [101.8-479] in MV group, p = 0.0009) as well as ICU length of stay 576.2 hours [457.5-652.8] in ECMO group vs. 322.2 hours [120.6-569.3] in MV group, p = 0.012).

CONCLUSION

ECMO is a supportive intervention for COVID-19 associated pneumonia that could be considered if the optimum mechanical ventilation is deemed ineffective. Biomarkers such as D-dimer, LDH, and troponin could help with discerning the clinical prognosis in patients with COVID-19 pneumonia.

COVID-19 patient bridged to recovery with veno-venous extracorporeal membrane oxygenation

BACKGROUND

In severe cases, the coronavirus disease 2019 (COVID-19) viral pathogen produces hypoxic respiratory failure unable to be adequately supported by mechanical ventilation. The role of extracorporeal membrane oxygenation (ECMO) remains unknown, with the few publications to date lacking detailed patient information or management algorithms all while reporting excessive mortality.

METHODS

Case report from a prospectively maintained institutional ECMO database for COVID-19.

RESULTS

We describe veno-venous (VV) ECMO in a COVID-19-positive woman with hypoxic respiratory dysfunction failing mechanical ventilation support while prone and receiving inhaled pulmonary vasodilator therapy. After 9 days of complex management secondary to her hyperdynamic circulation, ECMO support was successfully weaned to supine mechanical ventilation and the patient was ultimately discharged from the hospital.

CONCLUSIONS

With proper patient selection and careful attention to hemodynamic management, ECMO remains a reasonable treatment option for patients with COVID-19.

Invasive Mechanical Ventilation in Chronic Obstructive Pulmonary Disease Exacerbations

Chronic obstructive pulmonary disease (COPD) continues to be an important cause of morbidity, mortality, and health care costs worldwide. Although there exist some heterogeneity between patients, the course of COPD is characterized by recurrent acute exacerbations, which are among the most common causes of medical admission to hospital. Patients with frequent exacerbations have accelerated lung function decline, worse quality of life, and greater mortality. Therefore, interest is growing in assessing the effectiveness of interventions used to treat exacerbations. The present review summarizes the current evidence regarding the use of ventilatory management to treat COPD and the implementation of novel cost-effective strategies, such as high-flow oxygenation or extracorporeal carbon dioxide removal to improve clinical outcomes and functional recovery in this disease and to reduce the associated costs.

Organ donation in patients on extracorporeal membrane oxygenation: considerations for determination of death and withdrawal of life support

The use of extracorporeal membrane oxygenation (ECMO) is increasing globally, although mortality in this setting remains high. Patients on ECMO may be potential organ donors in the context of withdrawal of life-sustaining measures (WLSM) or neurologic determination of death (NDD). Nevertheless, there are currently no Canadian standards to guide clinicians on NDD or WLSM for the purposes of organ donation in this patient population. Apnea testing remains fundamental to determining NDD and is an area where ECMO may alter routine procedures. In this review, we outline protocols for the performance of apnea testing and WLSM for patients supported with ECMO, highlighting important technical and physiologic considerations that may affect the determination of death. In addition, we review important considerations for NDD in ECMO, including management of potential confounders, strategies for controlling oxygen and carbon dioxide levels during apnea testing, and the appropriate use of ancillary tests to support NDD. In the context of ECMO support, there is limited evidence to guide NDD and WLSM for the purposes of organ donation. Drawing upon extensive clinical experience, we provide protocols for these processes and review other important considerations in an effort to maximize donor potential in this growing patient population.

Does extracorporeal membrane oxygenation attenuate hypoxic pulmonary vasoconstriction in a porcine model of global alveolar hypoxia?

BACKGROUND

During severe respiratory failure, hypoxic pulmonary vasoconstriction (HPV) is partly suppressed, but may still play a role in increasing pulmonary vascular resistance (PVR). Experimental studies suggest that the degree of HPV during severe respiratory failure is dependent on pulmonary oxygen tension (PvO₂ ). Therefore, it has been suggested that increasing PvO₂ by veno-venous extracorporeal membrane oxygenation (V-V ECMO) would adequately reduce PVR in V-V ECMO patients.

OBJECTIVE

Whether increased PvO₂ by V-V ECMO decreases PVR in global alveolar hypoxia.

METHODS

Nine landrace pigs were ventilated with a mixture of oxygen and nitrogen. After 15 minutes of stable ventilation and hemodynamics, the animals were cannulated for V-V ECMO. Starting with alveolar normoxia, the fraction of inspiratory oxygen (F_I O₂ ) was stepwise reduced to establish different degrees of alveolar hypoxia. PvO₂ was increased by V-V ECMO.

RESULTS

V-V ECMO decreased PVR (from 5.5 [4.5-7.1] to 3.4 [2.6-3.9] mm Hg L^-1  min, P = .006) (median (interquartile range),) during ventilation with F_I O₂ of 0.15. At lower F_I O₂ , PVR increased; at F_I O₂ 0.10 to 4.9 [4.2-7.0], P = .036, at F_I O₂ 0.05 to 6.0 [4.3-8.6], P = .002, and at F_I O₂ 0 to 5.4 [3.5 - 7.0] mm Hg L^-1  min, P = .05.

CONCLUSIONS

The effect of increased PvO₂ by V-V ECMO on PVR depended highly on the degree of alveolar hypoxia. Our results partly explain why V-V ECMO does not always reduce right ventricular afterload at severe alveolar hypoxia.

Extra-corporeal membrane oxygenation for severe respiratory failure in the UK

An overview of the current system for referrals and management of severe respiratory failure in the United Kingdom. We outline the history of severe respiratory failure centres, the process of retrieving a patient for veno-venous extra corporeal membrane oxygenation and highlight some common difficulties and pitfalls when referring these critically unwell patients.

Duration of sweep gas off trial for weaning from venovenous extracorporeal membrane oxygenation

Background:

No data are available on the duration of time needed to assess the adequacy of lung function after stopping sweep gas for weaning of venovenous extracorporeal membrane oxygenation (ECMO). The objective of this study was to investigate changes in arterial blood gases (ABGs) during sweep gas off trials in patients receiving venovenous ECMO.

Methods:

Data on patients receiving venovenous ECMO, with a weaning trial at least once, were collected prospectively from January 2012 through December 2017. Serial changes in ABGs during sweep gas off trial and clinical outcomes after weaning from venovenous ECMO were evaluated.

Results:

Over the study period, 192 sweep gas off trials occurred in 93 patients: 115 (60%) failed and 77 (40%) were successful. During the trial, significant changes in blood gases were observed within 1 h in all patients. When serial ABGs were compared according to trial off results, there were no significant differences in the pH, PaCO₂, and HCO₃⁻ trends across time points between successful and failed trials. However, PaO₂ (70.6 versus 93.4 mmHg), SaO₂ (91.9 versus 95.2%), and PaO₂/FiO₂ ratio (164.0 versus 233.4) were significantly lower in failed trials than successful trials within 1 h after stopping sweep gas. After 2 h of trial off, no significant change in blood gases was observed until the end of the trial.

Conclusions:

No change in blood gases was observed 2 h after stopping sweep gas in patients receiving venovenous ECMO. Based on our institutional experience, however, we suggest monitoring for 2 h or more after stopping sweep gas flow to assess if patients are ready for decannulation.

The reviews of this paper are available via the supplemental material section.

Fluid Balance and Recovery of Native Lung Function in Adult Patients Supported by Venovenous Extracorporeal Membrane Oxygenation and Continuous Renal Replacement Therapy

Fluid overload is associated with increased mortality in adult patients with acute respiratory distress syndrome. In patients requiring venovenous extracorporeal membrane oxygenation (VV-ECMO), the effects of fluid removal on survival and lung recovery remain undefined. We assessed the impact of early fluid removal in adult patients supported by VV-ECMO and concomitant continuous renal replacement therapy, in an 18-bed tertiary intensive care unit between 2010 and 2015. Twenty-four patients met inclusion criteria, of these 15 (63%) survived to hospital discharge. In our patient group, a more negative cumulative daily fluid balance was strongly associated with improved pulmonary compliance (2.72 ml/cmH2O per 1 L negative fluid balance; 95% confidence interval [CI]: 1.61-3.83; P < 0.001). In addition, a more negative mean daily fluid balance was associated with improved pulmonary compliance (4.37 ml/cmH2O per 1 L negative fluid balance; 95% CI: 2.62-6.13; P < 0.001). Survivors were younger and had lower mean daily fluid balance (-0.33 L [95% CI: -1.22 to -0.06] vs. -0.07 L [95% CI: -0.76 to 0.06]; P = 0.438) and lower cumulative fluid balance up to day 14 (-4.60 L [95% CI: -8.40 to -1.45] vs. -1.00 L [95% CI: -4.60 to 0.90]; P = 0.325), although the fluid balance effect alone did not reach statistical significance.

In vitro characterization of PrismaLung+: a novel ECCO2R device

BACKGROUND

Invasive mechanical ventilation is lifesaving in the setting of severe acute respiratory failure but can cause ventilation-induced lung injury. Advances in extracorporeal CO₂ removal (ECCO₂R) technologies may facilitate more protective lung ventilation in acute respiratory distress syndrome, and enable earlier weaning and/or avoid invasive mechanical ventilation entirely in chronic obstructive pulmonary disease exacerbations. We evaluated the in vitro CO₂ removal capacity of the novel PrismaLung+ ECCO₂R device compared with two existing gas exchangers.

METHODS

The in vitro CO₂ removal capacity of the PrismaLung+ (surface area 0.8 m², Baxter) was compared with the PrismaLung (surface area 0.35 m², Baxter) and A.L.ONE (surface area 1.35 m², Eurosets) devices, using a closed-loop bovine blood-perfused extracorporeal circuit. The efficacy of each device was measured at varying pCO₂ inlet (p_inCO₂) levels (45, 60, and 80 mmHg) and blood flow rates (Q_B) of 200-450 mL/min; the PrismaLung+ and A.L.ONE devices were also tested at a Q_B of 600 mL/min. The amount of CO₂ removed by each device was assessed by measurement of the CO₂ infused to maintain circuit equilibrium (CO₂ infusion method) and compared with measured CO₂ concentrations in the inlet and outlet of the CO₂ removal device (blood gas analysis method).

RESULTS

The PrismaLung+ device performed similarly to the A.L.ONE device, with both devices demonstrating CO₂ removal rates ~ 50% greater than the PrismaLung device. CO₂ removal rates were 73 ± 4.0, 44 ± 2.5, and 72 ± 1.9 mL/min, for PrismaLung+, PrismaLung, and A.L.ONE, respectively, at Q_B 300 mL/min and p_inCO₂ 45 mmHg. A Bland-Altman plot demonstrated that the CO₂ infusion method was comparable to the blood gas analysis method for calculating CO₂ removal. The resistance to blood flow across the test device, as measured by pressure drop, varied as a function of blood flow rate, and was greatest for PrismaLung and lowest for the A.L.ONE device.

CONCLUSIONS

The newly developed PrismaLung+ performed more effectively than PrismaLung, with performance of CO₂ removal comparable to A.L.ONE at the flow rates tested, despite the smaller membrane surface area of PrismaLung+ versus A.L.ONE. Clinical testing of PrismaLung+ is warranted to further characterize its performance.

The use of extracorporeal carbon dioxide removal in acute chronic obstructive pulmonary disease exacerbation: a narrative review

Chronic obstructive pulmonary disease (COPD) exacerbation induces hypercapnic respiratory acidosis. Extracorporeal carbon dioxide removal (ECCO2R) aims to eliminate blood carbon dioxide (CO2) in order to reduce adverse effects from hypercapnia and the related acidosis. Hypercapnia has deleterious extra-pulmonary consequences in increasing intracranial pressure and inducing and/or worsening right heart failure. During COPD exacerbation, the use of ECCO2R may improve the efficacy of non-invasive ventilation (NIV) in terms of CO2 removal, decrease respiratory rate and reduce dynamic hyperinflation and intrinsic positive end expiratory pressure, which all contribute to increasing dead space. Moreover, ECCO2R may prevent NIV failure while facilitating the weaning of intubated patients from mechanical ventilation. In this review of the literature, the authors will present the current knowledge on the pathophysiology related to COPD, the principles of the ECCO2R technique and its role in acute and severe decompensation of COPD. However, despite technical advances, there are only case series in the literature and few prospective studies to clearly establish the role of ECCO2R in acute and severe COPD decompensation.

Transfusion strategies in non-bleeding critically ill adults: a clinical practice guideline from the European Society of Intensive Care Medicine

OBJECTIVE

To develop evidence-based clinical practice recommendations regarding transfusion practices in non-bleeding, critically ill adults.

DESIGN

A task force involving 13 international experts and three methodologists used the GRADE approach for guideline development.

METHODS

The task force identified four main topics: red blood cell transfusion thresholds, red blood cell transfusion avoidance strategies, platelet transfusion, and plasma transfusion. The panel developed structured guideline questions using population, intervention, comparison, and outcomes (PICO) format.

RESULTS

The task force generated 16 clinical practice recommendations (3 strong recommendations, 13 conditional recommendations), and identified five PICOs with insufficient evidence to make any recommendation.

CONCLUSIONS

This clinical practice guideline provides evidence-based recommendations and identifies areas where further research is needed regarding transfusion practices and transfusion avoidance in non-bleeding, critically ill adults.

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.

Comparison of estimation of cardiac output using an uncalibrated pulse contour method and echocardiography during veno-venous extracorporeal membrane oxygenation

Introduction:

During veno-venous extracorporeal membrane oxygenation, cardiac output monitoring is essential to assess tissue oxygen delivery. Adequate arterial oxygenation depends on the ratio between the extracorporeal pump blood flow and the cardiac output. The aim of this study was to compare estimates of cardiac output and blood flow/cardiac output ratios made using an uncalibrated pulse contour method with those made using echocardiography in patients treated with veno-venous extracorporeal membrane oxygenation.

Methods:

Cardiac output was estimated simultaneously using a pulse contour method (MostCareUp; Vygon, Encouen, France) and echocardiography in 17 hemodynamically stable patients treated with veno-venous extracorporeal membrane oxygenation. Comparisons were made using Bland–Altman and linear regression analysis.

Results:

There were significant correlations between cardiac output estimated using pulse contour method and echocardiography and between blood flow/cardiac output estimated using pulse contour method and blood flow/cardiac output estimated using echocardiography (r = 0.84, p < 0.001 and r = 0.87, p < 0.001, respectively). Bland–Altman analysis showed a good agreement (bias −0.20 ± 0.50 L/min) and a low percentage of error (25%) for the cardiac output values estimated by the two methods. The bias between the blood flow/cardiac output ratios obtained with the two methods was 5.19% ± 12.3% (percentage of error = 28.1%).

Conclusions:

The pulse contour method is a valuable alternative to echocardiography for the assessment of cardiac output and the blood flow/cardiac output ratio in patients treated with veno-venous extracorporeal membrane oxygenation.

Bedside troubleshooting during venovenous extracorporeal membrane oxygenation (ECMO)

In this review, we discuss common difficulties that clinicians may encounter while managing patients treated with venovenous (VV) extracorporeal membrane oxygenation (ECMO). ECMO is an increasingly important tool for managing severe respiratory failure that is refractory to conventional therapies. Its overall goal is to manage respiratory failure-induced hypoxemia and hypercarbia to allow "lung rest" and promote recovery. Typically, by the time VV-ECMO is initiated, the patient's pulmonary condition requires conventional ventilator settings that are detrimental to lung recovery or that exceed the remaining functional lung's ability to maintain acceptable physiological conditions. Standard mechanical ventilation can activate inflammation and worsen the pulmonary damage caused by the underlying disease, leading to ventilator-induced lung injury. In contrast, VV-ECMO facilitates lung-protective ventilation, decreasing further ventilator-induced lung injury and allowing lung recovery. Such lung-protective ventilation seeks to avoid barotrauma (by monitoring transpulmonary pressure), volutrauma (by reducing excessive tidal volume to promote lung rest), atelectotrauma [by maintaining adequate positive end-expiratory pressure (PEEP)], and oxygen toxicity (by decreasing ventilator oxygen levels when PEEP is adequate). ECMO for adult respiratory failure was associated with overall survival of 62% in 2018, according to the Extracorporeal Life Support Organization (ELSO) January 2019 registry report. Difficulties that may arise during VV-ECMO require timely diagnosis and optimal management to achieve the most favorable outcomes. These difficulties include ventilation issues, hypoxemia (especially as related to recirculation or low ECMO-flow-to-cardiac-output ratio), sepsis, malfunctioning critical circuit components, lack of clarity regarding optimal hemoglobin levels, hematological/anticoagulation complications, and right ventricular (RV) dysfunction. A culture of safety should be emphasized to optimize patient outcomes. A properly functioning team-not only the bedside clinician, but also nurses, perfusionists, respiratory therapists, physical therapists, pharmacists, nutritionists, and other medical specialists and allied health personnel-is vital for therapeutic success.

Extracorporeal carbon dioxide removal for acute hypercapnic respiratory failure

In the past, the only treatment of acute exacerbations of obstructive diseases with hypercapnic respiratory failure refractory to medical treatment was invasive mechanical ventilation (IMV). Considerable technical improvements transformed extracorporeal techniques for carbon dioxide removal in an attractive option to avoid worsening respiratory failure and respiratory acidosis, and to potentially prevent or shorten the duration of IMV in patients with exacerbation of COPD and asthma. In this review, we will present a summary of the pathophysiological rationale and evidence of ECCO₂R in patients with severe exacerbations of these pathologies.

Safety and efficacy of beta-blockers to improve oxygenation in patients on veno-venous ECMO

PURPOSE

Beta-blockers (BB) may improve oxygenation in patients on veno-venous extracorporeal membrane oxygenation (V-V ECMO). This study analyzed safety and efficacy of BB in hypoxemic patients on V-V ECMO.

MATERIALS AND METHODS

Retrospective analysis of patients who were treated with BB during V-V ECMO in two centers. The primary safety outcome was a composite of occurrence of bradycardia or hypotension with need for intervention, resuscitation, unexplained rise in serum lactate, and discontinuation of beta-blockers for other reasons than inefficacy or resolution on hypoxemia during the first 5 days of therapy. The main efficacy outcome was increase in oxygen saturation (SaO₂) within 12 h after start of BB.

RESULTS

33 patients received BB for 4 [3-7] days while on V-V ECMO. Fifteen episodes of adverse events occurred in 13 patients (39%); BB had to be discontinued in only one patient for sustained hypotension. In two other patients, doses were reduced or temporarily withheld due to bradycardia. There was an increase in SaO₂ from 92 [90-96]% to 96 [94-97]% at 12 h, with unchanged mean arterial pressure and norepinephrine doses.

CONCLUSIONS

In this study, use of BB in hypoxemic patients on V-V ECMO was safe and associated with a moderate increase in SaO₂.

Oxygen delivery, carbon dioxide removal, energy transfer to lungs and pulmonary hypertension behavior during venous-venous extracorporeal membrane oxygenation support: a mathematical modeling approach

Objective

To describe (1) the energy transfer from the ventilator to the lungs, (2) the match between venous-venous extracorporeal membrane oxygenation (ECMO) oxygen transfer and patient oxygen consumption (VO₂), (3) carbon dioxide removal with ECMO, and (4) the potential effect of systemic venous oxygenation on pulmonary artery pressure.

Methods

Mathematical modeling approach with hypothetical scenarios using computer simulation.

Results

The transition from protective ventilation to ultraprotective ventilation in a patient with severe acute respiratory distress syndrome and a static respiratory compliance of 20mL/cm H₂O reduced the energy transfer from the ventilator to the lungs from 35.3 to 2.6 joules/minute. A hypothetical patient, hyperdynamic and slightly anemic with VO₂ = 200mL/minute, can reach an arterial oxygen saturation of 80%, while maintaining the match between the oxygen transfer by ECMO and the VO₂ of the patient. Carbon dioxide is easily removed, and normal PaCO₂ is easily reached. Venous blood oxygenation through the ECMO circuit may drive the PO₂ stimulus of pulmonary hypoxic vasoconstriction to normal values.

Conclusion

Ultraprotective ventilation largely reduces the energy transfer from the ventilator to the lungs. Severe hypoxemia on venous-venous-ECMO support may occur despite the matching between the oxygen transfer by ECMO and the VO₂ of the patient. The normal range of PaCO₂ is easy to reach. Venous-venous-ECMO support potentially relieves hypoxic pulmonary vasoconstriction.

Management of cardiogenic shock in patients with acute coronary syndromes

Cardiogenic shock remains a major problem affecting a large proportion of patients with acute coronary syndromes, with a persistent high mortality rate. Although mechanical reperfusion with percutaneous coronary intervention has improved outcomes following acute coronary syndromes, there is limited evidence supporting the other current treatments used to manage patients with cardiogenic shock (intra-aortic balloon pumps, percutaneous left ventricular assist devices and extracorporeal membrane oxygenation). This article looks at these options, assessing current evidence and recent advances. It also discusses areas that still require research to ensure there is improvement in these high-risk patients, such as coordinated regionalised approaches to cardiogenic shock management with multidisciplinary care provided in designated tertiary shock centres.

A mathematical model of CO2, O2 and N2 exchange during venovenous extracorporeal membrane oxygenation

Background

Venovenous extracorporeal membrane oxygenation (vv-ECMO) is an effective treatment for severe respiratory failure. The interaction between the cardiorespiratory system and the oxygenator can be explored with mathematical models. Understanding the physiology will help the clinician optimise therapy. As others have examined O₂ exchange, the main focus of this study was on CO₂ exchange.

Methods

A model of the cardiorespiratory system during vv-ECMO was developed, incorporating O₂, CO₂ and N₂ exchange in both the lung and the oxygenator. We modelled lungs with shunt fractions varying from 0 to 1, covering the plausible range from normal lung to severe acute respiratory distress syndrome. The effects on P_aCO₂ of varying the input parameters for the cardiorespiratory system and for the oxygenator were examined.

Results

P_aCO₂ increased as the shunt fraction in the lung and metabolic CO₂ production rose. Changes in haemoglobin and F_IO₂ had minimal effect on P_aCO₂. The effect of cardiac output on P_aCO₂ was variable, depending on the shunt fraction in the lung.

P_aCO₂ decreased as extracorporeal circuit blood flow was increased, but the changes were relatively small in the range used clinically for vv-ECMO of > 2 l/min. P_aCO₂ decreased as gas flow to the oxygenator rose and increased with recirculation. The oxygen fraction of gas flow to the oxygenator had minimal effect on P_aCO₂.

Conclusions

This mathematical model of gas exchange during vv-ECMO found that the main determinants of P_aCO₂ during vv-ECMO were pulmonary shunt fraction, metabolic CO₂ production, gas flow to the oxygenator and extracorporeal circuit recirculation.

Electronic supplementary material

The online version of this article (10.1186/s40635-018-0183-4) contains supplementary material, which is available to authorized users.

[Extracorporeal membrane oxygenation : System selection, (contra)indications, and management]

There are a large number of extracorporeal membrane oxygenation (ECMO) systems and configurations. Thorough planning and evaluation of specific therapeutic needs are necessary to tailor ECMO therapy to the individual patient situation. Indications tend towards lowering the threshold towards respiratory ECMO. Patients with severe acute respiratory distress syndrome (ARDS) not improving to optimization of ventilation and supportive therapeutic measures potentially qualify for ECMO. Contraindications are relative and have to be considered in the light of the individual risk-benefit ratio. The same is true for decisions to stop ECMO therapy in case of futility for which reliable evidence does not exist.

Echocardiography in extracorporeal life support: A key player in procedural guidance, tailoring and monitoring

Extracorporeal life support (ECLS) is a mainstay of current practice in severe respiratory, circulatory or cardiac failure refractory to conventional management. The inherent complexity of different ECLS modes and their influence on the native pulmonary and cardiovascular system require patient-specific tailoring to optimize outcome. Echocardiography plays a key role throughout the ECLS care, including patient selection, adequate placement of cannulas, monitoring, weaning and follow-up after decannulation. For this purpose, echocardiographers require specific ECLS-related knowledge and skills, which are outlined here.

Adjunctive therapies during veno-venous extracorporeal membrane oxygenation

Veno-venous extracorporeal membrane oxygenation (VV ECMO) restores gas exchanges in severely hypoxemic patients. The need for adjunctive therapies usually originates either from refractory hypoxemia during ECMO (defined as the persistence of low blood oxygen levels despite extracorporeal support) or from the attempt to give a specific therapy for acute respiratory distress syndrome (ARDS). In this review, therapeutic strategies to treat refractory and persistent hypoxemia during ECMO are evaluated. In the second part, therapies that can be added on top of VV ECMO to address inflammation and altered vascular permeability in ARDS are examined. The therapies currently available often allow for an effective treatment of hypoxemia during ECMO. ARDS is still lacking a specific therapy, with low-grade evidence sustaining the majority of currently used drugs.

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.

Cerebral Pathophysiology in Extracorporeal Membrane Oxygenation: Pitfalls in Daily Clinical Management

Extracorporeal membrane oxygenation (ECMO) is a life-saving technique that is widely being used in centers throughout the world. However, there is a paucity of literature surrounding the mechanisms affecting cerebral physiology while on ECMO. Studies have shown alterations in cerebral blood flow characteristics and subsequently autoregulation. Furthermore, the mechanical aspects of the ECMO circuit itself may affect cerebral circulation. The nature of these physiological/pathophysiological changes can lead to profound neurological complications. This review aims at describing the changes to normal cerebral autoregulation during ECMO, illustrating the various neuromonitoring tools available to assess markers of cerebral autoregulation, and finally discussing potential neurological complications that are associated with ECMO.

Right ventricular dysfunction during acute respiratory distress syndrome and veno-venous extracorporeal membrane oxygenation

Severe ARDS can be complicated by right ventricular (RV) failure. The etiology of RV failure in ARDS is multifactorial. Vascular alterations, hypoxia, hypercapnia and effects of mechanical ventilation may play a role. Echocardiography has an important role in diagnosing RV failure in ARDS patients. Once extracorporeal membrane oxygenation (ECMO) is indicated in these patients, the right ECMO modus needs to be chosen. In this review, the etiology, diagnosis and management of RV failure in ARDS will be briefly outlined. The beneficial effect of veno-venous (VV) ECMO on RV function in these patients will be illustrated. Based on this, we will give recommendations regarding choice of ECMO modus and provide an algorithm for management of RV failure in VV ECMO supported patients.

Oxygenator performance and artificial-native lung interaction

During extracorporeal membrane oxygenation (ECMO), oxygen (O₂) transfer (V'O₂) and carbon dioxide (CO₂) removal (V'CO₂) are partitioned between the native lung (NL) and the membrane lung (ML), related to the patient's metabolic-hemodynamic pattern. The ML could be assimilated to a NL both in a physiological and a pathological way. ML O₂ transfer (V'O₂ML) is proportional to extracorporeal blood flow and the difference in O₂ content between each ML side, while ML CO₂ removal (V'CO₂ML) can be calculated from ML gas flow and CO₂ concentration at sweep gas outlet. Therefore, it is possible to calculate the ML gas exchange efficiency. Due to the ML aging process, pseudomembranous deposits on the ML fibers may completely impede gas exchange, causing a "shunt effect", significantly correlated to V'O₂ML decay. Clot formation around fibers determines a ventilated but not perfused compartment, with a "dead space effect", negatively influencing V'CO₂ML. Monitoring both shunt and dead space effects might be helpful to recognise ML function decline. Since ML failure is a common mechanical complication, its monitoring is critical for right ML replacement timing and it also important to understand the ECMO system performance level and for guiding the weaning procedure. ML and NL gas exchange data are usually obtained by non-continuous measurements that may fail to be timely detected in critical situations. A real-time ECMO circuit monitoring system therefore might have a significant clinical impact to improve safety, adding relevant clinical information. In our clinical practise, the integration of a real-time monitoring system with a set of standard measurements and samplings contributes to improve the safety of the procedure with a more timely and precise analysis of ECMO functioning. Moreover, an accurate analysis of NL status is fundamental in clinical setting, in order to understand the complex ECMO-patient interaction, with a multi-dimensional approach.

Cannulation technique: femoro-femoral

The cannulation technique used during veno-venous extracorporeal membrane oxygenation (VV ECMO) insertion can have a major impact on a patients' overall outcome. We have developed a technique that aims to combine speed and effectiveness, with minimal risk. The steps include: (I) percutaneous cannulation using the Seldinger technique; (II) ultrasound guided access and positioning of cannulas; (III) femoro-femoral circuit configuration with a later option of high flow; (IV) a no skin cut serial dilation technique; (V) non-suturing securing of cannulas and (VI) a non-surgical manual pressure technique of explantation. The following is a discussion around these techniques and their various advantages and disadvantages.

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

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

Comparison of mortality prediction models in acute respiratory distress syndrome undergoing extracorporeal membrane oxygenation and development of a novel prediction score: the PREdiction of Survival on ECMO Therapy-Score (PRESET-Score)

Background

Extracorporeal membrane oxygenation (ECMO) is a life-saving therapy in acute respiratory distress syndrome (ARDS) patients but is associated with complications and costs. Here, we validate various scores supposed to predict mortality and develop an optimized categorical model.

Methods

In a derivation cohort, 108 ARDS patients (2010–2015) on veno-venous ECMO were retrospectively analysed to assess four established risk scores (ECMOnet-Score, RESP-Score, PRESERVE-Score, Roch-Score) for mortality prediction (receiver operating characteristic analysis) and to identify by multivariable logistic regression analysis independent variables for mortality to yield the new PRESET-Score (PREdiction of Survival on ECMO Therapy-Score). This new score was then validated both in independent internal (n = 82) and external (n = 59) cohorts.

Results

The median (25%; 75% quartile) Sequential Organ Failure Assessment score was 14 (12; 16), Simplified Acute Physiology Score II was 62.5 (57; 72.8), median intensive care unit stay was 17 days (range 1–124), and mortality was 62%. Only the ECMOnet-Score (area under curve (AUC) 0.69) and the RESP-Score (AUC 0.64) discriminated survivors and non-survivors. Admission pH_a, mean arterial pressure, lactate, platelet concentrations, and pre-ECMO hospital stay were independent predictors of death and were used to build the PRESET-Score. The score’s internal (AUC 0.845; 95% CI 0.76–0.93; p < 0.001) and external (AUC 0.70; 95% CI 0.56–0.84; p = 0.008) validation revealed excellent discrimination.

Conclusions

While our data confirm that both the ECMOnet-Score and the RESP-Score predict mortality in ECMO-treated ARDS patients, we propose a novel model also incorporating extrapulmonary variables, the PRESET-Score. This score predicts mortality much better than previous scores and therefore is a more precise choice for decision support in ARDS patients to be placed on ECMO.

Surgery for a large tracheoesophageal fistula using extracorporeal membrane oxygenation

We report a patient with a giant tracheoesophageal fistula (TEF) planned for reconstructive surgery. Because mechanical ventilation in any form was technically impossible, we successfully used veno-venous extracorporeal membrane oxygenation (VV-ECMO) without the need for mechanical ventilation.

Retrieval of severe acute respiratory failure patients on extracorporeal membrane oxygenation: Any impact on their outcomes?

OBJECTIVE

Mobile extracorporeal membrane oxygenation (ECMO) retrieval teams (MERTs) assure ECMO implantation and under-ECMO retrieval of patients with most severe acute respiratory failure (ARF) to experienced ECMO centers. Although described as feasible, mobile ECMO has only been poorly evaluated in comparison with on-site implantation. This study was undertaken to compare the indications, characteristics, and outcomes of MERT-implanted patients with venovenous (VV)-ECMO versus those implanted on site in our intensive care unit (ICU).

METHODS

Retrospective, single-center study.

RESULTS

Among 157 VV-ECMO implantations from 2008 to 2012, the MERT hooked up 118 (75%) patients with refractory ARF, as reflected by their median partial pressure of O₂ in arterial blood/fraction of inspired oxygen of 58 (interquartile range, 50-73). ARF was accompanied by severe multiorgan failure, with a median Simplified Acute Physiology Score-II of 71 (61-81), median Sequential Organ Failure Assessment score of 14 (10-16), and with 82% of the patients receiving inotropes. All patients were transported by ground ambulance: median distance was 15 (6-25) km, and median transport time was 35 (25-35) minutes, during which no major ECMO system-related event occurred. For the MERT- and on-site-implanted groups, ICU mortality was comparable (46.6% vs 53.8%, respectively, P = .5), as were ECMO-related complication rates (53.4% of MERT vs 53.8% of on-site-implanted groups, P = 1.0). According to multivariable analysis, MERT ECMO implantation was not associated with ICU mortality (odds ratio, 1.1; 95% confidence interval, 0.4-2.7; P = .85).

CONCLUSIONS

ICU mortality and ECMO-related complications of patients with MERT-implanted VV-ECMO who were transferred to our ECMO referral center were comparable with those implanted on site by the same team, thereby supporting this strategy to manage patients with severe ARF.

An extracorporeal carbon dioxide removal (ECCO2R) device operating at hemodialysis blood flow rates

Background

Extracorporeal carbon dioxide removal (ECCO₂R) systems have gained clinical appeal as supplemental therapy in the treatment of acute and chronic respiratory injuries with low tidal volume or non-invasive ventilation. We have developed an ultra-low-flow ECCO₂R device (ULFED) capable of operating at blood flows comparable to renal hemodialysis (250 mL/min). Comparable operating conditions allow use of minimally invasive dialysis cannulation strategies with potential for direct integration to existing dialysis circuitry.

Methods

A carbon dioxide (CO₂) removal device was fabricated with rotating impellers inside an annular hollow fiber membrane bundle to disrupt blood flow patterns and enhance gas exchange. In vitro gas exchange and hemolysis testing was conducted at hemodialysis blood flows (250 mL/min).

Results

In vitro carbon dioxide removal rates up to 75 mL/min were achieved in blood at normocapnia (pCO₂ = 45 mmHg). In vitro hemolysis (including cannula and blood pump) was comparable to a Medtronic Minimax oxygenator control loop using a time-of-therapy normalized index of hemolysis (0.19 ± 0.04 g/100 min versus 0.12 ± 0.01 g/100 min, p = 0.169).

Conclusions

In vitro performance suggests a new ultra-low-flow extracorporeal CO₂ removal device could be utilized for safe and effective CO₂ removal at hemodialysis flow rates using simplified and minimally invasive connection strategies.

Fifty Years of Research in ARDS. Is Extracorporeal Circulation the Future of Acute Respiratory Distress Syndrome Management?

Mechanical ventilation (MV) remains the cornerstone of acute respiratory distress syndrome (ARDS) management. It guarantees sufficient alveolar ventilation, high Fi_O2 concentration, and high positive end-expiratory pressure levels. However, experimental and clinical studies have accumulated, demonstrating that MV also contributes to the high mortality observed in patients with ARDS by creating ventilator-induced lung injury. Under these circumstances, extracorporeal lung support (ECLS) may be beneficial in two distinct clinical settings: to rescue patients from the high risk for death associated with severe hypoxemia, hypercapnia, or both not responding to maximized conventional MV, and to replace MV and minimize/abolish the harmful effects of ventilator-induced lung injury. High extracorporeal blood flow venovenous extracorporeal membrane oxygenation (ECMO) may therefore rescue the sickest patients with ARDS from the high risk for death associated with severe hypoxemia, hypercapnia, or both not responding to maximized conventional MV. Successful venovenous ECMO treatment in patients with extremely severe H1N1-associated ARDS and positive results of the CESAR trial have led to an exponential use of the technology in recent years. Alternatively, lower-flow extracorporeal CO₂ removal devices may be used to reduce the intensity of MV (by reducing Vt from 6 to 3-4 ml/kg) and to minimize or even abolish the harmful effects of ventilator-induced lung injury if used as an alternative to conventional MV in nonintubated, nonsedated, and spontaneously breathing patients. Although conceptually very attractive, the use of ECLS in patients with ARDS remains controversial, and high-quality research is needed to further advance our knowledge in the field.