Membrane lung dead space and membrane lung impairment: An exploratory retrospective study in COVID-19 patients.

BackgroundVeno-venous extracorporeal membrane oxygenation (VV ECMO) is a key therapy for refractory respiratory failure, but can trigger systemic inflammation and prothrombotic activation that impair the membrane lung (ML). ML dysfunction can lead to mechanical failure of extracorporeal support, severe hypoxemia, and the need for urgent or elective circuit replacement. Conventional single parameters (pressure drop, post-ML blood gases, hemoglobin saturation), and laboratory tests have limited ability to predict ML deterioration.MethodsWe conducted a single-center pilot retrospective study including 27 ECMO circuits from 20 adult patients with COVID-19-related acute respiratory failure. Membrane lung dead space (DSML) was calculated from ML exhaust carbon dioxide (CO2) and blood gas measurements and used to assess ML effectiveness. For each circuit we evaluated the association between DSML and subsequent circuit exchange.Results20 patients (27 ECMO circuits) were analyzed; 10 circuits required replacement. Circuits that were replaced showed higher DSML values and lower CO2 concentration in membrane lung exhaust gas and membrane lung CO2 removal compared with circuits that completed the run. CO2-derived variables were the only parameters that differed significantly between groups, while oxygenation-related measures and baseline characteristics were similar.ConclusionsIn this exploratory study conducted on COVID-19 patients, we found an association between DSML increase and membrane lung impairment. However, the analysis does not provide enough information to assess the predictive performance of DSML. The identification of a significant threshold for circuit exchange requires further validation in larger prospective and multicenter studies.