Current knowledge gaps in extracorporeal respiratory support

Abstract

Extracorporeal life support (ECLS) for acute respiratory failure encompasses veno-venous extracorporeal membrane oxygenation (V-V ECMO) and extracorporeal carbon dioxide removal (ECCO₂R). V-V ECMO is primarily used to treat severe acute respiratory distress syndrome (ARDS), characterized by life-threatening hypoxemia or ventilatory insufficiency with conventional protective settings. It employs an artificial lung with high blood flows, and allows improvement in gas exchange, correction of hypoxemia, and reduction of the workload on the native lung. On the other hand, ECCO₂R focuses on carbon dioxide removal and ventilatory load reduction ("ultra-protective ventilation") in moderate ARDS, or in avoiding pump failure in acute exacerbated chronic obstructive pulmonary disease. Clinical indications for V-V ECLS are tailored to individual patients, as there are no absolute contraindications. However, determining the ideal timing for initiating extracorporeal respiratory support remains uncertain. Current ECLS equipment faces issues like size and durability. Innovations include intravascular lung assist devices (ILADs) and pumpless devices, though they come with their own challenges. Efficient gas exchange relies on modern oxygenators using hollow fiber designs, but research is exploring microfluidic technology to improve oxygenator size, thrombogenicity, and blood flow capacity. Coagulation management during V-V ECLS is crucial due to common bleeding and thrombosis complications; indeed, anticoagulation strategies and monitoring systems require improvement, while surface coatings and new materials show promise. Moreover, pharmacokinetics during ECLS significantly impact antibiotic therapy, necessitating therapeutic drug monitoring for precise dosing. Managing native lung ventilation during V-V ECMO remains complex, requiring a careful balance between benefits and potential risks for spontaneously breathing patients. Moreover, weaning from V-V ECMO is recognized as an area of relevant uncertainty, requiring further research. In the last decade, the concept of Extracorporeal Organ Support (ECOS) for patients with multiple organ dysfunction has emerged, combining ECLS with other organ support therapies to provide a more holistic approach for critically ill patients. In this review, we aim at providing an in-depth overview of V-V ECMO and ECCO₂R, addressing various aspects of their use, challenges, and potential future directions in research and development.

Keywords: Acute respiratory failure; Gas exchange; Lung protective ventilation; V-V ECMO.

Fig. 1

Extracorporeal oxygen delivery ($\dot{V}$ O_2ML)/total oxygen consumption ($\dot{V}$ O_2TOT) and extracorporeal carbon dioxide removal ($\dot{V}$ CO_2ML)/total carbon dioxide production ($\dot{V}$ CO_2TOT) as a function of extracorporeal blood flow (BF) at steady state in an adult patient. $\dot{V}$ O_2TOT = 250 mL/min and $\dot{V}$ CO_2TOT 200 mL/min. Veno-venous extracorporeal oxygenation support (V-V ECMO), veno-venous extracorporeal CO₂ removal (V-V ECCO₂R)