Bedside electrical impedance tomography (EIT) could be useful to visualize evolving pulmonary perfusion distributions when acute respiratory distress syndrome (ARDS) worsens or in response to ventilatory and positional therapies. In experimental ARDS, we evaluated the agreement of EIT and dynamic-contrast enhanced computed tomography (CT) perfusion distributions at two injury timepoints, and in response to increased PEEP and prone position.
Eleven mechanically ventilated (VT 8ml⋅kg -1) Yorkshire pigs (5 male, 6 female) received bronchial hydrochloric acid (HCl, 3.5ml⋅kg -1) to invoke lung injury. EIT and CT perfusion images were obtained at two-hours (early injury), and 24-hours (late injury) after injury in supine position with PEEP 5cmH2O and 10cmH2O. In 8 animals, EIT and CT perfusion imaging were also conducted in the prone position. EIT perfusion (QEIT) and CT perfusion (QCT) values (as percent of image total) were compared in 8 vertical regions across injury stages, levels of PEEP, and body positions using mixed effects linear regression. The primary outcome was agreement between QEIT and QCT, defined using limits of agreement (LoA) and Pearson correlation coefficient.
PaO2/FiO2 decreased over the course of the experiment (healthy to early injury: -253; 95% CI, -317 to -189, early to late injury: -88; 95% CI, -151 to -24). The LoA between QEIT and QCT was -4.66% and 4.73% for the middle 50% quantile of average regional perfusion, and the correlation coefficient was 0.88; 95% CI 0.86 to 0.90, P<0.001. EIT and CT showed similar perfusion redistributions over injury stages and in response to increased PEEP. QEIT redistributions after positional therapy underestimated QCT in ventral regions and overestimated QCT in dorsal regions.
EIT closely approximated CT perfusion measures in experimental ARDS, in supine position, over injury progression and with increased PEEP. Further validation is needed to determine the accuracy of EIT in measuring perfusion redistributions after positional changes.