Derecruitment volume assessment derived from pressure-impedance curves with electrical impedance tomography in experimental acute lung injury

Objective: To investigate the accuracy of derecruitment volume (V_DER) assessed by pressure-impedance (P-I) curves derived from electrical impedance tomography (EIT).

Methods: Six pigs with acute lung injury received decremental positive end-expiratory pressure (PEEP) from 15 to 0 in steps of 5 cmH₂O. At the end of each PEEP level, the pressure-volume (P-V) curves were plotted using the low constant flow method and release maneuvers to calculate the V_DER between the PEEP of setting levels and 0 cmH₂O (V_DER-PV). The V_DER derived from P-I curves that were recorded simultaneously using EIT was the difference in impedance at the same pressure multiplied by the ratio of tidal volume and corresponding tidal impedance (V_DER-PI). The regional P-I curves obtained by EIT were used to estimate V_DER in the dependent and nondependent lung.

Results: The global lung V_DER-PV and V_DER-PI showed close correlations (r = 0.948, P<0.001); the mean difference was 48 mL with limits of agreement of -133 to 229 mL. Lung derecruitment extended into the whole process of decremental PEEP levels but was unevenly distributed in different lung regions.

Conclusions: P-I curves derived from EIT can assess V_DER and provide a promising method to estimate regional lung derecruitment at the bedside.