Electrical impedance tomography compared to positron emission tomography for the measurement of regional lung ventilation: an experimental study

Introduction Electrical impedance tomography (EIT), which can assess regional lung ventilation at the bedside, has never been compared with positron-emission tomography (PET), a goldstandard to quantify regional ventilation. This experiment systematically compared both techniques in injured and noninjured lungs. Methods The study was performed in six mechanically ventilated female piglets. In normal lungs, tidal volume (VT) was randomly changed to 6, 8, 10 and 15 ml/kg on zero endexpiratory pressure (ZEEP), then, at VT 10 ml/kg, positive endexpiratory pressure (PEEP) was randomly changed to 5, 10 and 15 cmH2O. Afterwards, acute lung injury (ALI) was subsequently created in three animals by injecting 3 ml/kg hydrochloric acid into the trachea. Then at PEEP 5 cmH2O, VT was randomly changed to 8 and 12 ml/kg and PEEP of 10 and 15 cmH2O applied at VT 10 ml/kg. EIT and PET examinations were performed simultaneously. EIT ventilation (V TEIT ) and lung volume (VL) were measured in the anterior and posterior area of each lung. On the same regions of interest, ventilation (V PET ) and aerated lung volume (VAatten) were determined with PET. Results On ZEEP, VTEIT and VPET significantly correlated for global (V TEIT = VPET - 2E-13, R2 = 0.95, P < 0.001) and regional (VTEIT = 0.81VPET+7.65, R2 = 0.63, P < 0.001) ventilation over both conditions. For ALI condition, corresponding R2 were 0.91 and 0.73 (P < 0.01). Bias was = 0 and limits of agreement were -37.42 and +37.42 ml/min for global ventilation over both conditions. These values were 0.04 and -29.01 and +29.08 ml/ min, respectively, for regional ventilation. Significant correlations were also found between VL and VAatten for global (VL = VA atten +1E-12, R2 = 0.93, P < 0.0001) and regional (V L = 0.99VAatten+0.92, R2 = 0.65, P < 0.001) volume. For ALI condition, corresponding R2 were 0.94 (P < 0.001) and 0.54 (P < 0.05). Bias was = 0 and limits of agreement ranged -38.16 and +38.16 ml for global ventilation over both conditions. These values were -0.24 and -31.96 to +31.48 ml, respectively, for regional ventilation.