The Difference of Lung Volume Change Detected by Electrical Impedance Tomography (EIT) Between Noninvasive Positive-pressure Ventilation (NIPPV) Support by Nasal Pillow and High Flow Nasal Cannula in Post-extubation Patients

Electrical impedance tomography can effectively monitor the lung volume change in ICU patients who were under mechanical ventilator or noninvasive positive pressure ventilator support. Continuous positive airway pressure (CPAP) support by nasal pillow and high flow nasal cannula can improve inspiratory function in extubated patients . However, the extent of lung volume change or functional residual volume (FRC) change by using these two devices were never surveyed before in extubated patients. The investigators will check end-expiratory lung volume (EELV) ,anterior, medio-anterior, medio-posterior and posterior EELV by electrical impedance tomography after use of these two devices in extubated patients.