The Pendelluft phenomenon is an important cause of lung damage in spontaneously breathing mechanically ventilated patients since it considerably increases the stress on the lung parenchyma in the dependent areas. It can result in a local driving pressure up to three times higher than the global driving pressure. The measurement of Pendelluft is still uncertain in the literature, and although various methods have been proposed, not all have the same meaning in terms of pulmonary overstress and overstrain. This study proposes a comparative analysis of different ways to calculate and estimate the stress imposed on the lung parenchyma by Pendelluft in terms of regional volume and local driving pressure through electrical impedance tomography.
Patients under invasive mechanical ventilation intubated due to respiratory failure in pressure support mode (weaning phase)
Age less than 18 years; sedation or neuromuscular blockade; absence of respiratory effort; contraindications to esophageal balloon cathether positioning or electrical impedance tomography belt positioning; presence of pneumothorax or active air leaks; hemodynamic instability; absence of informed consent.
Single group
Pressure Support Variation and Calculation of Respiratory Mechanics
Other interventionPatients will be submitted to different levels of pressure support (PS) in a randomly assigned order. First 30 minutes shall be recorded at the clinical PS. Next, blood gas samples shall be collected. Subsequently, three inspiratory pauses of at least 2 seconds shall be performed with an interval of at least 8 respiratory cycles between them. The same shall be performed with three expiratory pauses. Next, the PS shall be varied to 50% less or 50% more than clinical PS (based on randomization) and the same procedures shall be performed after 30 minutes of data recording (blood gas sample collection, inspiratory and expiratory pauses). All data shall be analyzed offline using a software that will be able to compare three different methods to calculate Pendelluft magnitude based on the literature. After completion of the protocol, ventilatory parameters shall be returned to the original settings. If the patient becomes tachypneic during lower PS, the protocol shall be interrupted.
1. Magnitude of Pendelluft
Three differents methods of estimating magnitude of Pendelluft shall be compared using a software based on electrical impedance tomography monitoring (Enlight 2100, Timpel Medical®, Brazil)
2. Magnitude of Pendelluft during inspiratory pause
One of the methods of Pendelluft measurement shall be performed during an inspiratory pause for comparison with a normal cycle (without pause).
3. Magnitude of respiratory effort
Respiratory effort shall be estimated through expiratory pauses and though recording of esophageal pressure at different pressure support levels. These data shall be compared to Pendelluft magnitude according to the different methods of calculation
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