Incremental and Decremental PEEP Titration by Diverse Strategies in Subjects with ARDS: a Prospective Physiological Study

Inclusion Criteria: * Intubated and mechanical ventilated patients in ICU within 48 hours * Be over 18 years old * With moderate-severe ARDS (PaO2 /FIO2 ,200 mm Hg) Exclusion Criteria: * Severe chronic obstructive pulmonary diseases * Pulmonary bulla(\>1CM) or pneumothorax or pneumomediastinum or subcutaneous emphysema * Pregnancy * BMI≥35kg/m2 * Suspected pulmonary vascular hemorrhage * Disturbance of consciousness or intracranial hypertension * Severe cardiac dysfunction (New York Heart Association Class III or IV, acute -Coronary syndrome or persistent ventricular tachyarrhythmia), cardiogenic shock or after major cardiac surgery * Hemodynamic instability (i.e., mean arterial pressure \[MAP\]\<60 mm Hg despite vasopressor use * The medical team considering short periods of high pressure to be unsafe * Contraindications for placement of esophageal pressure catheters (e.g., esophageal varix or fracture of skull base) * Contraindications for EIT monitoring (including pacemaker, or cutaneous diseases which limiting electrode placement) * Agonal stage or end-stages of diseases