Use of Electrical Impedance Tomography (EIT) to Estimate Global and Regional Lung Recruitment Volume (VREC) Induced by Positive End-Expiratory Pressure (PEEP): An Experiment in Pigs with Lung Injury.

BACKGROUND Electrical impedance tomography (EIT) is a real-time tool used to monitor lung volume change at the bedside, which could be used to measure lung recruitment volume (VREC) for setting positive end-expiratory pressure (PEEP). We assessed and compared the agreement in VREC measurement with the EIT method versus the flow-derived method. MATERIAL AND METHODS In 12 Bama pigs, lung injury was induced by tracheal instillation of hydrochloric acid and verified by an arterial partial pressure of oxygen to inspired oxygen fraction ratio below 200 mmHg. During the end-expiratory occlusion, an airway release maneuver was conduct at 5 and 15 cmH₂O of PEEP. VREC was measured by flow-integrated PEEP-induced lung volume change (flow-derived method) and end-expiratory lung impedance change (EIT-derived method). Linear regression and Bland-Altman analysis were used to test the correlation and agreement between these 2 measures. RESULTS Lung injury was successfully induced in all the animals. EIT-derived VREC was significantly correlated with flow-derived VREC (R²=0.650, p=0.002). The bias (the lower and upper limits of agreement) was -19 (-182 to 144) ml. The median (interquartile range) of EIT-derived VREC was 322 (218-469) ml, with 110 (59-142) ml and 194 (157-307) ml in dependent and nondependent lung regions, respectively. Global and regional respiratory system compliance increased significantly at high PEEP compared to those at low PEEP. CONCLUSIONS Close correlation and agreement were found between EIT-derived and flow-derived VREC measurements. The advantages of EIT-derived recruitability assessment included the avoidance of ventilation interruption and the ability to provide regional recruitment information.