Acute respiratory distress syndrome (ARDS) is the common disease in clinical,which pathophysiology is a lot of alveolar collapse and heterogeneity. Recruitment maneuver is one of the important therapy for improvement of this phenomenon. The previous research focuses on the hemodynamic and oxygenation effect of recruitment maneuver on the lung of ARDS. Seldom investigators try to find the intuitive change of heterogeneity when recruitment maneuver is implemented. In this study, the investigators compare three recruitment maneuvers on the lung heterogeneity of ARDS.~Electrical impedance tomography (EIT) has been introduced as a true bedside and radiation-free technique which provides information on heterogeneity. The investigators compare effects of three recruitment maneuvers on lung heterogeneity before recruitment maneuver and do the same thing after three recruitment maneuvers.~Ninety-three patients with ARDS will be enrolled . These patients are treated routinly.They need to recept a time of ZEEP (PEEP is zero cmH2O)for ten respiratory cycles before RM(recruitment maneuvers).Implemente a kind of RM at random immediately after ZEEP,Then make the ventilator same as before ZEEP.The EIT images ,blood gases and hemodynamic variables will be examined as beseline between ZEEP and RM.Completion of this kind of RM lies that the P/F of blood gases 3 minutes after RM achieves (1) PO2/FiO2>400mmHg or (2)PO2/FiO2+PCO2 ≥ 400mmHg(FiO2=1)，(3)the difference between this index before lung recriument and after lung recriument PO2/FiO2<5%.In addition,3 minutes after RM,compare the indexs above between three methods.
Acute respiratory distress syndrome (ARDS) is the common disease in clinical, which pathophysiology is a lot of alveolar collapse and heterogeneity. Recruitment maneuver is one of the important therapy for improvement of this phenomenon. The previous research focuses on the hemodynamic and oxygenation effect of recruitment maneuver on the lung of ARDS. Seldom investigators try to find the intuitive change of heterogeneity when recruitment maneuver is implemented. In this study, the investigators compare three recruitment maneuvers on the lung heterogeneity of ARDS.