Bedside Contribution of Electrical Impedance Tomography to Set Positive End-Expiratory Pressure for ECMO-Treated Severe ARDS Patients.

Abstract Optimal positive end-expiratory pressure (PEEP) is unknown in severe acute respiratory distress syndrome (ARDS) patients on extracorporeal membrane oxygenation (ECMO) receiving mechanical ventilation with very low tidal volume. To evaluate electrical impedance tomography's (EIT) ability to monitor a PEEP trial and to derive from EIT the best compromise PEEP in this setting. A decremental PEEP trial (20-0 cmH2O) in 5 cmH2O steps was monitored by EIT, with lung images divided into four ventral-to-dorsal horizontal regions of interest. The EIT-based PEEP providing the best compromise between overdistension and collapsed zones was arbitrarily defined as the lowest pressure able to limit EIT-assessed collapse to ≤15% with the least overdistension. Driving pressure was maintained constant at 14 cmH2O in pressure controlled mode. Tidal volume, static compliance, tidal impedance variation, end-expiratory lung impedance and their respective regional distributions were visualized at each PEEP level in 15 patients on ECMO. Low tidal volume (2.9-4 mL/kg ideal body weight) and poor compliance (12.1-18.7 mL/cm H2O) were noted, with significantly higher tidal volume and compliance at PEEP10 and PEEP5 than PEEP20. EIT-based best compromise PEEPs were 15, 10 and 5cmH2O for 7, 6, and 2 patients, respectively, while PEEP20 and PEEP0 were never selected. The broad variability in optimal PEEP observed in these severe ARDS patients under ECMO reinforces the need for personalized titration of ventilation settings. EIT may be an interesting non-invasive bedside tool to provide real-time monitoring of the PEEP impact in these patients.