The aim of this study is to assess the effects and safety of the early application of BILEVEL-APRV protocol and conventional ventilation strategy that used low tidal volume and adequate PEEP level in ARDS patients .

Although mechanical ventilation is life-sustaining for patients with ARDS, it can perpetuate lung injury. A number of recent advances have greatly improved in the mechanical ventilation strategies and treatment for acute respiratory distress syndrome (ARDS), however, Mortality remains high, even with the use of low tidal volume and adequate positive end expiratory pressure(PEEP). Numerous experimental showed that the BILEVEL-APRV mode used in animal ARDS model can improve gas exchanges and hemodynamic tolerance of the ventilation while reducing the dosage for sedative drugs.

The aim of this single-center, prospective, randomized, controlled, open study is to compare the effects and safety of the early application of BILEVEL-APRV protocol and conventional ventilation strategy that used low tidal volume and adequate PEEP level in ARDS patients .

Inclusion Criteria:

• Acute respiratory distress syndrome,according to the Berlin definition of ARDS, - The receipt of endotracheal mechanical ventilation for a period was no longer than 48 hours
• A ratio of the partial pressure of arterial oxygen (PaO2) to the fraction of inspired oxygen(FiO2) was less than 250.

Exclusion Criteria:

• Pregnancy
• The expected duration of mechanical ventilation was less than 48 hours
• Intracranial hypertension (suspected or confirmed)
• Neuromuscular disorders that are known to prolong the need for mechanical ventilation
• Known or suspected chronic obstructive pulmonary disease(COPD)
• Preexisting conditions with an expected 6-month mortality exceeding 50%
• Pneumothorax (drained or not)at enrollment
• Treatment with extracorporeal support (ECMO) at enrollment
• There was a lack of commitment to life support.