Despite the advances in technology and ventilatory modes, mortality of ARDS is still around 40%. Besides prone positioning, the best approach of management is low tidal volume ventilation (LTV). This 'protective ventilation' strategy is not aways effective to improve oxygenation and is associated with an increased requirement of sedation and neuromuscular blocking agents, which increase length of stay and morbidity. APRV is a ventilatory mode based on relatively high and sustained continuous positive pressure, combined with a short phase of release to allow carbon dioxide removal. It also allows unrestricted spontaneous breathing throughout respiration, independent of the ventilator cycle. Providing sustained inflation while limiting duration and frequency of release phase permits limiting volume loss, resulting in progressive and improved alveolar recruitment, an increased alveolar surface area available for gas exchange and improved ventilation-perfusion matching.

In this multi-center, prospective, randomized, controlled, open trial, the investigators aim to compare the effects and safety of the early application of time-controlled adaptive method of APRV and conventional ventilation with LTV strategy in patients with severe to moderate ARDS.