In mechanically ventilated patients during supine position, alveolar collapse usually distributes in dependent lung region.Decrease of flow trigger sensitivity might improve homogeneous of tidal volume distribution.

In mechanically ventilated patients during supine position, alveolar collapse usually distributes in dependent lung region. High positive end expiratory pressure (PEEP) has been applied to improve the homogeneous distribution of ventilation by increasing the end expiratory lung ventilation (EELV) and alveolar recruitment. However, for patients who increasing PEEP in some extent still existed poor aeration in the dependent region, further elevating PEEP seems to be unreasonable that perhaps lead to overdistension. Decreasing trigger sensitivity might further evoke inspiratory efforts to improve the ventilation for this type of patients.The Electrical impedance tomography (EIT) was applied in monitoring the regional ventilation distribution at the bedside.

Inclusion Criteria:

1. The post operative patients who received pressure support ventilation;
2. After the clinical PEEP was evaluated 5cmH2O, the tidal volume distribution still existed heterogeneity.

Exclusion Criteria:

1. Under 18 years;
2. History of diaphragm dysfunction and surgery;
3. Central respiratory drive dysfunction;
4. history of esophageal, gastric or lung surgery;
5. The contraindication of using EIT (pacemaker, defibrillator, and implantable pumps).

The postoperative patients receiving pressure support ventilation and existing heterogenous ventilation.