Acute respiratory distress syndrome (ARDS) accounts for 10% of all ICU admissions and for 23% of patients requiring mechanical ventilation (MV). Its hospital mortality remains high, ranging from 34% in mild forms up to 46% in severe cases. Positive pressure MV remains the cornerstone of management, but at the same time it can contribute to worsening and maintenance of the lung injury when excessive stress and strain is applied to the lung parenchima (so-called ventilator-induced lung injury, VILI). VILI significantly contributes to the morbidity and mortality of ARDS patients, and it has been clearly demonstrated that protective (low-volume, low-pressure) MV settings are associated with a significant survival benefit. Unfortunately, in a certain proportion of ARDS cases, it is difficult to preserve acceptable gas exchange while maintaining protective ventilation settings, due to a high ventilatory load. In these cases, extracorporeal CO2 removal (ECCO2R) can be applied to grant the application of protective or even ultra-protective mechanical ventilation settings. The main outcome of this multicenter, prospective, randomized, comparative open trial is to determine whether early ECCO2R allowing ultraprotective mechanical ventilation improves the outcomes of patients with moderate ARDS.