PMC8519369_01
A Global EIT signal waveform in arbitrary units (AU) acquired in a supine patient suffering from COVID-19 related ARDS during two incremental and four decremental steps in positive end-expiratory pressure (PEEP) (top). The blue arrows show the amplitude of tidal impedance variation (TIV) during ventilation at the initial PEEP value and the change in end-expiratory lung impedance at the last PEEP value compared to the beginning of the manoeuvre. The numbers above the waveform present the set PEEP values in cmH2O. Regional Delta end-expiratory lung impedance in ventral and dorsal lung regions relative to the initial values at the lowest PEEP (bottom left) demonstrate the more pronounced increase in the dependent regions, implying recruitment. Chest CT scan (bottom right) was obtained on Day 1 of ICU admission.
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At this level, the increase in end-expiratory lung impedance was twice as much as the tidal impedance variation at the initial PEEP setting of 10 cmH2O (Fig. 1). The increase in end-expiratory lung impedance was more pronounced in the dorsal than in the ventral region (Fig. 1 bottom left).
The figure shows the analysis of regional lung ventilation in a supine patient with COVID-19 related ARDS using EIT, carried out during two incremental and four decremental steps in positive end-expiratory pressure (PEEP). Functional EIT images of regional tidal impedance variation (TIV) (top) show the distribution of tidal volume in the chest cross-section. Ventilated areas are presented in white and blue colors, the numbers below the images give the global sums of TIV values in percent of initial value at PEEP of 10 cmH2O. Functional EIT images of regional changes in TIV (DeltaTIV) (middle) highlight the local increases (light blue areas) and decreases (orange areas) in ventilation at individual PEEP values in comparison with the initial lowest PEEP. The numbers below the images specify the relative changes in TIV in ventral and dorsal lung regions in comparison with the initial TIV distribution at the start of the manoeuvre. Ventilation profiles (bottom) show the distribution of ventilation in the right and left lung regions along the ventrodorsal chest diameter. White horizontal lines in each profile indicate the location of the centre of ventilation (CoV) with the corresponding values plotted below each profile. Values smaller than 50% imply preferential ventilation distribution towards ventral regions.
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The PEEP was lowered, with a step of 2 cmH2O, from 20 cmH2O until the lungs could be ventilated evenly (Fig. 2), and the PEEP level of 14 cmH2O was sufficient to maintain the dorsal ventilation.