Clinical implementation of electric impedance tomography in the treatment of ARDS: a single centre experience

Abstract

To report on our clinical experience using EIT in individualized PEEP titration in ARDS. Using EIT assessment, we optimized PEEP settings in 39 ARDS patients. The EIT PEEP settings were compared with the physicians' PEEP settings and the PEEP settings according to the ARDS network. We defined a PEEP difference equal to or greater than 4 cm H₂O as clinically relevant. Changes in lung compliance and PaO₂/FiO₂-ratio were compared in patients with EIT-based PEEP adjustments and in patients with unaltered PEEP. In 28% of the patients, the difference in EIT-based PEEP and physician-PEEP was clinically relevant; in 36%, EIT-based PEEP and physician-PEEP were equal. The EIT-based PEEP disagreed with the PEEP settings according to the ARDS network. Adjusting PEEP based upon EIT led to a rapid increase in lung compliance and PaO₂/FiO₂-ratio. However, this increase was also observed in the group where the PEEP difference was less than 4 cm H₂O. We hypothesize that this can be attributed to the alveolar recruitment during the PEEP trial. EIT based individual PEEP setting appears to be a promising method to optimize PEEP in ARDS patients. The clinical impact, however, remains to be established.

Keywords: Acute respiratory distress syndrome; Electrical impedance tomography; Mechanical ventilation; Positive end expiratory pressure.

Fig. 1

Changes in end-expiratory lung impedance (EELI) values at different decremental PEEP levels reflect the stepwise fall in end-expiratory lung volume (global: overall tidal impedance change; ROI 1 to ROI 4 represent tidal impedance chance from ventral, mid-ventral, mid-dorsal and dorsal region). During the last PEEP step there is a gradual decrease in EELI in ROI 2 reflecting alveolar derecruitment. In ROI 3 and 4 the decrease in EELI starts at earlier PEEP steps (delta-Z tidal impedance variations)

Fig. 2

Alveolar overdistension and alveolar collapse (OD/CL)

Fig. 3

Bland Altman plot of differences in PEEP between EIT guided PEEP and the PEEP set by the physician. The size of the dot is an indicator for the incidence of the value. The red dashed line indicates a PEEP difference of 4 cm H₂O

Fig. 4

Bland Altman plot of differences in PEEP between the ARDS network table and EIT guided PEEP. The size of the dot is an indicator for the incidence of the value. The red dashed line indicates a PEEP difference of 4 cm H₂O

Fig. 5

Bland Altman plot of differences in PEEP between EIT guided PEEP and PEEP based on best Cdyn. The size of the dot is an indicator for the incidence of the value. The red dashed line indicates a PEEP difference of 4 cm H₂O

Fig. 6

Acute changes in Cdyn in 39 mechanically ventilated ARDS patients after EIT in the group where pre-EIT PEEP was < 4 cm H₂O (group A) different from EIT-advised PEEP and a group where the difference between pre-EIT and EIT-advised PEEP was ≥ 4 cm H₂O (group B). There was a significant increase in the Cdyn (p < 0.001), however this increase was not significantly different between both groups (p = 0.151 for interaction, 2-way ANOVA)

Fig. 7

Acute changes in PaO₂/FiO₂-ratio in 39 mechanically ventilated ARDS patients after EIT in the group where pre-EIT PEEP was < 4 cm H₂O (group A) different from EIT-advised PEEP and a group where the difference between pre-EIT and EIT-advised PEEP was ≥ 4 cm H₂O (group B). There was a significant increase in the PaO₂/FiO₂-ratio (p < 0.001), however this increase was not significantly different between both groups (p = 0.894 for interaction, 2-way ANOVA)

Fig. 8

Changes in EELI in four regions of regions of interest during the PEEP trial (V ventral, MV mid-ventral, MD mid-dorsal, D dorsal). There is a large drop of EELI in the mid-dorsal and dorsal region when PEEP was decreased below 18 cm H₂O. PEEP was set at 20 cm H₂O in this patient (dEELI delta-end expiratory lung impedance, AU arbitrary units)

Fig. 9

Changes in EELI in four regions of regions of interest during the PEEP trial (V ventral, MV mid-ventral, MD mid-dorsal, D dorsal). At the end of the PEEP trial EELI returns to baseline. PEEP was set at 10 cm H₂O in this patient (dEELI delta-end expiratory lung impedance, AU arbitrary units)

Fig. 10

Changes in EELI in four regions of regions of interest during the PEEP trial (V ventral, MV mid-ventral, MD mid-dorsal, D dorsal). At the end of the PEEP trial EELI is higher compared to baseline. PEEP was set at 10 cm H₂O in this patient (dEELI delta-end expiratory lung impedance, AU arbitrary units)