Standardized liberation trials in patients with COVID-19 ARDS treated with venovenous extracorporeal membrane oxygenation: when ready, let them breathe!

Modification of Respiratory Drive and Lung Stress by Level of Support Pressure and ECMO Sweep Gas Flow in Patients With Severe COVID-19-Associated Acute Respiratory Distress Syndrome: an Exploratory Retrospective Analysis

OBJECTIVES

Patients with severe acute respiratory distress syndrome (ARDS) often exhibit an unusually strong respiratory drive, which predisposes them to effort-induced lung injury. Careful titration of support pressure via the ventilator and carbon dioxide removal via extracorporeal membrane oxygenation (ECMO) may attenuate respiratory drive and lung stress.

DESIGN

A retrospective cohort study.

SETTING

At a single center, a university hospital.

PARTICIPANTS

Ten patients with severe COVID-19-associated ARDS (CARDS) on venovenous ECMO therapy.

INTERVENTIONS

Assessment of the effect of titrated support pressure and titrated ECMO sweep gas flow on respiratory drive and lung stress in spontaneously breathing patients during ECMO therapy.

MEASUREMENTS AND MAIN RESULTS

Airway occlusion pressure (P0.1) and the total swing of the transpulmonary pressure were determined as surrogate parameters of respiratory drive and lung stress. Ventilator-mediated elevation of support pressure decreased P0.1 but increased transpulmonary driving pressure, airway pressure, tidal volume, and end-inspiratory transpulmonary occlusion pressure. The increase in ECMO sweep gas flow lowered P0.1, transpulmonary pressures, tidal volume, and respiratory frequency linearly.

CONCLUSIONS

In patients with CARDS on pressure support ventilation, even moderate support pressure may lead to overassistance during assisted ventilation, which is only reflected by advanced monitoring of respiratory mechanics. Modifying carbon dioxide removal via the extracorporeal system profoundly affects respiratory effort and mechanics. Spontaneously breathing patients with CARDS may benefit from consequent carbon dioxide removal.

Liberation From Venovenous Extracorporeal Membrane Oxygenation for Respiratory Failure: A Scoping Review

BACKGROUND

Safe and timely liberation from venovenous extracorporeal membrane oxygenation (ECMO) would be expected to reduce the duration of ECMO, the risk of complications, and costs. However, how to liberate patients from venovenous ECMO effectively remains understudied.

RESEARCH QUESTION

What is the current state of the evidence on liberation from venovenous ECMO?

STUDY DESIGN AND METHODS

We systematically searched for relevant publications on liberation from venovenous ECMO in Medline and EMBASE. Citations were included if the manuscripts provided any of the following: criteria for readiness for liberation, a liberation protocol, or a definition of successful decannulation or decannulation failure. We included randomized trials, observational trials, narrative reviews, guidelines, editorials, and commentaries. We excluded single case reports and citations where the full text was unavailable.

RESULTS

We screened 1,467 citations to identify 39 key publications on liberation from venovenous ECMO. We then summarized the data into five main topics: current strategies used for liberation, criteria used to define readiness for liberation, conducting liberation trials, criteria used to proceed with decannulation, and parameters used to predict decannulation outcomes.

INTERPRETATION

Practices on liberation from venovenous ECMO are heterogeneous and are influenced strongly by clinician preference. Additional research on liberation thresholds is needed to define optimal liberation strategies and to close existing knowledge gaps in essential topics on liberation from venovenous ECMO.

Physiological adaptations during weaning from veno-venous extracorporeal membrane oxygenation

Veno-venous extracorporeal membrane oxygenation (V-V ECMO) has an established evidence base in acute respiratory distress syndrome (ARDS) and has seen exponential growth in its use over the past decades. However, there is a paucity of evidence regarding the approach to weaning, with variation of practice and outcomes between centres. Preconditions for weaning, management of patients' sedation and mechanical ventilation during this phase, criteria defining success or failure, and the optimal duration of a trial prior to decannulation are all debated subjects. Moreover, there is no prospective evidence demonstrating the superiority of weaning the sweep gas flow (SGF), the extracorporeal blood flow (ECBF) or the fraction of oxygen of the SGF (FdO2), thereby a broad inter-centre variability exists in this regard. Accordingly, the aim of this review is to discuss the required physiological basis to interpret different weaning approaches: first, we will outline the physiological changes in blood gases which should be expected from manipulations of ECBF, SGF and FdO2. Subsequently, we will describe the resulting adaptation of patients' control of breathing, with special reference to the effects of weaning on respiratory effort. Finally, we will discuss pertinent elements of the monitoring and mechanical ventilation of passive and spontaneously breathing patients during a weaning trial. Indeed, to avoid lung injury, invasive monitoring is often required in patients making spontaneous effort, as pressures measured at the airway may not reflect the degree of lung strain. In the absence of evidence, our approach to weaning is driven largely by an understanding of physiology.

Complications Associated With Venovenous Extracorporeal Membrane Oxygenation-What Can Go Wrong?

OBJECTIVES

Despite increasing use and promising outcomes, venovenous extracorporeal membrane oxygenation (V-V ECMO) introduces the risk of a number of complications across the spectrum of ECMO care. This narrative review describes the variety of short- and long-term complications that can occur during treatment with ECMO and how patient selection and management decisions may influence the risk of these complications.

DATA SOURCES

English language articles were identified in PubMed using phrases related to V-V ECMO, acute respiratory distress syndrome, severe respiratory failure, and complications.

STUDY SELECTION

Original research, review articles, commentaries, and published guidelines from the Extracorporeal Life support Organization were considered.

DATA EXTRACTION

Data from relevant literature were identified, reviewed, and integrated into a concise narrative review.

DATA SYNTHESIS

Selecting patients for V-V ECMO exposes the patient to a number of complications. Adequate knowledge of these risks is needed to weigh them against the anticipated benefit of treatment. Timing of ECMO initiation and transfer to centers capable of providing ECMO affect patient outcomes. Choosing a configuration that insufficiently addresses the patient's physiologic deficit leads to consequences of inadequate physiologic support. Suboptimal mechanical ventilator management during ECMO may lead to worsening lung injury, delayed lung recovery, or ventilator-associated pneumonia. Premature decannulation from ECMO as lungs recover can lead to clinical worsening, and delayed decannulation can prolong exposure to complications unnecessarily. Short-term complications include bleeding, thrombosis, and hemolysis, renal and neurologic injury, concomitant infections, and technical and mechanical problems. Long-term complications reflect the physical, functional, and neurologic sequelae of critical illness. ECMO can introduce ethical and emotional challenges, particularly when bridging strategies fail.

CONCLUSIONS

V-V ECMO is associated with a number of complications. ECMO selection, timing of initiation, and management decisions impact the presence and severity of these potential harms.