Estimation of deflation parameters as a surrogate for transpulmonary pressure from regional pressure-flow-curves derived from electrical impedance tomography in a porcine model of the acute respiratory distress syndrome.

Objective.Adjustment of positive end-expiratory pressure (PEEP) is part of lung-protective ventilation in patients with acute respiratory distress syndrome (ARDS) and can be performed invasively using an esophageal catheter (Talmoret al2008New Engl. J. Med.3592095-104). The objective of this proof-of-concept study was to investigate whether the transpulmonary pressure (TPP) of 0 mbar, at which alveolar collapse occurs, can be estimated non-invasively using electrical impedance tomography (EIT).Approach.ARDS was induced in 14 pigs by repeated lung lavage and a 2 h period of ventilator-induced lung injury ventilation. The TPP was calculated as the difference between end-expiratory airway pressure and the corresponding esophageal pressure. During a descending pressure-controlled ramp maneuver from 50 to 0 mbar, pressure-flow curves at the pixel levels of the candidate dependent lung region were generated and regional deflation parameters calculated.Main results.During the descending pressure ramp the beginning of alveolar collapse could be determined at approximately 25 mbar in the dependent region of the EIT images based on regional characteristic points in both lung conditions. A strong correlation was found (r= 0.929,B= 1.005,R2= 0.862,p= 0.007) in healthy lungs and an intermediate correlation (r= 0.817,B= 0.894,R2= 0.668,p= 0.025) in ARDS between the second characteristic point and the PEEP according to Talmor, corresponding to a TPP of 0.Significance.The findings of the study have demonstrated that EIT can identify regional characteristic points that correlate with regional TPP changes in the dependent lung region. This knowledge can be used to optimize a lung protective ventilation strategy by titrating TPP guided PEEP non-invasively.