Comparison of Different Methods to Calculate Pendelluft by Electrical Impedance Tomography in Mechanically Ventilated Patients

Comparison of Different Methods to Calculate Pendelluft by Electrical Impedance Tomography in Patients Undergoing Invasive Mechanical Ventilation Under Pressure Support Mode

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.

Respiratory mechanics and regional ventilation will be monitored by electrical impedance tomography (Enlight 1800 and 2100, Timpel). Esophageal and gastric pressures will be obtained by placing an esophageal/gastric balloon cathether (Nutrivent ®), validation concerning position will be done through modified Baydur maneuver (delta esophageal/delta airway pressure = 0.8-1.2). The hardware Pneumodrive will be used to inflate the balloon and store the airway, gastric and esophageal pressures.

Initially the patients will be monitored with EIT for aproximately 30 minutes after pletismography stabilization. Then, an arterial blood-gas sample shall be collected for analysis. Next, three expiratory and three inspiratory pauses of at least two seconds will be realized with intervals of eight respiratory cycles between them, allowing plateau pressure to be recorded and global and regional driving pressure to be estimated. All this data will be stored for later analysis. The same procedures and measurements shall be made sequentially with a 50% higher pressure support and with a 50% lower pressure support.

Inclusion Criteria:

• Patients under invasive mechanical ventilation intubated due to respiratory failure in pressure support mode (weaning phase)

Exclusion Criteria:

• 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.