Electrical impedance tomography monitoring in acute respiratory distress syndrome patients with mechanical ventilation during prolonged positive end-expiratory pressure adjustments

Background/purpose The time required to reach oxygenation equilibrium after positive end-expiratory pressure (PEEP) adjustments in mechanically ventilated patients with acute respiratory distress syndrome (ARDS) is unclear. We used electrical impedance tomography to elucidate gas distribution and factors related to oxygenation status following PEEP in patients with ARDS. Methods Nineteen mechanically ventilated ARDS patients were placed on baseline PEEP (PEEPB ) for 1 hour, PEEPB − 4 cmH2 O PEEP (PEEPL ) for 30 minutes, and PEEPB + 4 cmH2 O PEEP (PEEPH ) for 1 hour. Tidal volume and respiratory rate were similar. Impedance changes, respiratory parameters, and arterial blood gases were measured at baseline, 5 minutes, and 30 minutes after PEEPL , and 5 minutes, 15 minutes, 30 minutes, and 1 hour after PEEPH. Results PaO2 /fraction of inspired oxygen (P/F ratio) decreased quickly from PEEPB to PEEPL , and stabilized 5 minutes after PEEPL . However the P/F ratio progressively increased from PEEPL to PEEPH , and a significantly higher P/F ratio and end-expiratory lung impedance were found at 60 minutes compared to 5 minutes after PEEPH . The end-expiratory lung impedance level significantly correlated with P/F ratio ( p