Evaluation with electrical impedance tomography (EIT) of the application of a High-Frequency Chest Wall Oscillation device to clear airway secretions

INTERVENTION: Patients will be randomized in four treatments arms: 1) patients without airway secretions (i.e. < 2 bronchoaspiration/hour) and with no application of a recruitment maneuver (RM); 2) patients without airway secretions (i.e. < 2 bronchoaspiration/hour) and with the application of a RM; 3) patients with airway secretions (i.e. > 2 bronchoaspiration/hour) and with no application of a RM and 4) patients with airway secretions (i.e. > 2 bronchoaspiration/hour) and with the application of a RM. An EIT belt and a HFCWO inflatable belt will be applied on the chest. After setting the EIT machine to record, a baseline measurement will be recorded (Baseline), Patients will thereafter undergo to a session of 10 minutes of HFCWO device application at 12 Hz, as usual clinical practice. As soon as the treatment ends (T0), after 1 (T1) and 3 (T3) hours another EIT records will be taken. Each EIT recording will last 10 minutes. Airway suctioning with a closed system will be performed for around 20 seconds at around 30 seconds from record start. To patients randomized to receive a RM, the RM (30 cmH2O of positive airway pressure for 30 seconds) will be applied 1 minute and 30 seconds after the airway suctioning. CONDITION: Acute Respiratory Failure High‐Frequency Chest Wall Oscillation (HFCWO) Impaired cough with tracheobronchial secretion retention PRIMARY OUTCOME: To evaluate if the application of a HFCWO device will different influence the lung aeration (as assessed by the end‐expiratory lung impedence through EIT) in relation to: 1) the presence or absence of airway secretions and 2) the application of a RM. SECONDARY OUTCOME: To evaluate if the application of a HFCWO device will different influence the gas exchange (as assessed with arterial blood gases) in relation to: 1) the presence or absence of airway secretions and 2) the application of a RM. To evaluate if the application of a HFCWO device will different influence the tidal volume (as assessed by the tidal impedence variation through EIT) in relation to: 1) the presence or absence of airway secretions and 2) the application of a RM. To evaluate if the application of a HFCWO device will different influence vital parameters (i.e. heart rate and blood pressure) in relation to: 1) the presence or absence of airway secretions and 2) the application of a RM. INCLUSION CRITERIA: All the patients meeting the following criteria will be eligible for the study: 1) age equal or greater than 18 years; 2) presence of consciousness; 3) previous invasive mechanical ventilation > 48 hours.