Using lung ultrasound re-aeration score(LUS-RAS) combined with pressure-volume curve(PVC) adjust maintain positive end-expiratory pressure(PEEP) after recruitment maneuver, to achieve real-time adjustment, reduce ventilation-associated lung injury and the purpose of effective lung recruitment.

The traditional method, set PEEP according to PVC in ARDS mechanical ventilation, lacks morphological evaluation. For point-of-care lung ultrasound(POC-LUS) is non-invasive, real-time, visualization, no need transport patients, getting more and more attention in the ARDS treatment. It has been reported that LUS-RAS is a meaningful assessment in recruitment maneuver. This study will combine POC-LUS with PVC in set the initial peep, and then dynamic record LUS-RAS to feedback regulate PEEP. Using the POC-LUS and maximum oxygenation method to assess lung recruitment effect in experimental group and control group prospectively. The ventilator parameters, state of hemodynamic, arterial blood gas(ABG) in each group will be recorded; Statistical methods will be performed in term to understand the correlation.

Inclusion Criteria:

• patient aged 18 years and older
• ARDS patients with invasive mechanical ventilation

Exclusion Criteria:

• Intracranial hypertension
• Pneumothorax and mediastinal emphysema
• Severe hypoxemia (oxygenation index <100)
• Hemodynamic instability
• Chest deformity or surgical history
• Affect Lung-ultrasound conditions: subcutaneous emphysema, chest wound etc.