Bedside selection of positive end-expiratory pressure by electrical impedance tomography in hypoxemic patients: a feasibility study.

Background: Positive end-expiratory pressure (PEEP) is a key element of mechanical ventilation. It should optimize recruitment, without causing excessive overdistension, but controversy exists on the best method to set it. The purpose of the study was to test the feasibility of setting PEEP with electrical impedance tomography in order to prevent lung de-recruitment following a recruitment maneuver. We enrolled 16 patients undergoing mechanical ventilation with PaO ₂ /FiO ₂ <300 mmHg. In all patients, under constant tidal volume (6-8 ml/kg) PEEP was set based on the PEEP/FiO ₂ table proposed by the ARDS network (PEEP _ARDSnet ). We performed a recruitment maneuver and monitored the end-expiratory lung impedance (EELI) over 10 min. If the EELI signal decreased during this period, the recruitment maneuver was repeated and PEEP increased by 2 cmH ₂ O. This procedure was repeated until the EELI maintained a stability over time (PEEP _EIT ).
Results: The procedure was feasible in 87% patients. PEEP _EIT was higher than PEEP _ARDSnet (13 ± 3 vs. 9 ± 2 cmH ₂ O, p < 0.001). PaO ₂ /FiO ₂ improved during PEEP _EIT and driving pressure decreased. Recruited volume correlated with the decrease in driving pressure but not with oxygenation improvement. Finally, regional alveolar hyperdistention and collapse was reduced in dependent lung layers and increased in non-dependent lung layers.
Conclusions: In hypoxemic patients, a PEEP selection strategy aimed at stabilizing alveolar recruitment guided by EIT at the bedside was feasible and safe. This strategy led, in comparison with the ARDSnet table, to higher PEEP, improved oxygenation and reduced driving pressure, allowing to estimate the relative weight of overdistension and recruitment.