Inclusion Criteria:  invasive mechanical ventilation need for flexible bronchoscopy to remove secretion plug from the airway  Exclusion Criteria:  hemodynamic instability, (i.e. systolic arterial pressure <90 mmHg or mean systolic pressure <65 mmHg despite fluid repletion); need for vasoactive agents, i.e. vasopressin or epinephrine at any dosage, or norepinephrine >0.3 mcg/kg/min or dobutamine>5 mcg/kg/min; life-threatening arrhythmias or electrocardiographic signs of ischemia; contraindications to placement of Electrical Impedance Tomography belt, Lung UltraSound or application of a Recruiting Maneuver (i.e., pneumothorax, pulmonary emphysema, chest burns or thoracic surgery within 1 week); inclusion in other research protocols.