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 cmH(2)O. 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 cmH(2)O (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.