Bedside electrical impedance tomography could be useful to visualize evolving pulmonary perfusion distributions when acute respiratory distress syndrome worsens or in response to ventilatory and positional therapies. In experimental acute respiratory distress syndrome, this study evaluated the agreement of electrical impedance tomography and dynamic contrast–enhanced computed tomography perfusion distributions at two injury time points and in response to increased positive end-expiratory pressure (PEEP) and prone position.
Eleven mechanically ventilated (VT 8 ml · kg−1) Yorkshire pigs (five male, six female) received bronchial hydrochloric acid (3.5 ml · kg−1) to invoke lung injury. Electrical impedance tomography and computed tomography perfusion images were obtained at 2 h (early injury) and 24 h (late injury) after injury in supine position with PEEP 5 and 10 cm H2O. In eight animals, electrical impedance tomography and computed tomography perfusion imaging were also conducted in the prone position. Electrical impedance tomography perfusion (QEIT) and computed tomography perfusion (QCT) values (as percentages of image total) were compared in eight 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 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 limits of agreement between QEIT and QCT were −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). Electrical impedance tomography and computed tomography 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.
Electrical impedance tomography closely approximated computed tomography perfusion measures in experimental acute respiratory distress syndrome, in the supine position, over injury progression and with increased PEEP. Further validation is needed to determine the accuracy of electrical impedance tomography in measuring perfusion redistributions after positional changes.
- In patients with acute respiratory distress syndrome, alterations in regional pulmonary perfusion may markedly alter global oxygenation and have important clinical ramifications for the use of varying levels of positive end-expiratory pressure or positional therapy
- Contrast enhanced computed tomography has generally been considered the clinical gold standard for assessing ventilation-to-perfusion relationships, but the less invasive, radiation-free, and logistically less intensive technology, electrical impedance tomography, has been suggested as a viable alternative
- Quantitative data on electrical impedance tomography’s accuracy relative to computed tomography perfusion imaging have not been well delineated
- Using a porcine model of acute lung injury, the authors compared electrical impedance tomography and computed tomography perfusion images in eight vertical regions obtained at two injury time points in 11 animals, as well as in response to increasing positive end-expiratory pressure, and in eight animals, prone positioning, specifically evaluating the agreement between electrical impedance tomography and computed tomography regional perfusion measures
- Similar redistributions of perfusion over injury stages and between positive end-expiratory pressure levels were detected by the two modalities, although across the supine and prone positions, electrical impedance tomography underestimated blood flow in ventral regions and overestimated flow in dorsal regions