Dynamic relative regional lung strain estimated by computed tomography and electrical impedance tomography in ARDS patients.

In the acute distress respiratory syndrome (ARDS), specific lung regions can be exposed to excessive strain due to heterogeneous disease, gravity-dependent lung collapse and injurious mechanical ventilation. Computed tomography (CT) is the gold standard for regional strain assessment. An alternative tool could be the electrical impedance tomography (EIT). We aimed to determine whether EIT-based methods can predict the dynamic relative regional strain (DRRS) between two levels of end-expiratory pressure (PEEP) in gravity-non-dependent and dependent lung regions. Fourteen ARDS patients underwent CT and EIT acquisitions (at end-inspiratory and end-expiratory) at two levels of PEEP: a low-PEEP based on ARDS-net strategy and a high-PEEP titrated according to EIT. Three EIT-based methods for DRRS were compared to relative CT-based strain: (1) the change of the ratio between EIT ventilation and end-expiratory lung impedance in arbitrary units ([ΔZAU low-PEEP/EELIAU low-PEEP]/[ΔZAU high-PEEP/EELIAU high-PEEP]), (2) the change of ΔZ/EELI ratio calibrated to mL ([ΔZml low-PEEP/EELIml low-PEEP]/[ΔZml high-PEEP/EELIml high-PEEP]) using CT data, and (3) the relative change of ∆ZAU (∆ZAU low-PEEP/∆ZAU high-PEEP). We performed linear regressions analysis and calculated bias and limits of agreement to assess the performance of DRRS by EIT in comparison with CT. The DRRS assessed by (ΔZml low-PEEP/EELIml low-PEEP)/(ΔZml high-PEEP/EELIml high-PEEP) and ∆ZAU low-PEEP/∆ZAU high-PEEP showed good relationship and agreement with the CT method (R2 of 0.9050 and 0.8679, respectively, in non-dependent region; R2 of 0.8373 and 0.6588, respectively, in dependent region; biases ranging from - 0.11 to 0.51 and limits of agreement ranging from - 0.73 to 1.16 for both methods and lung regions). Conversely, DRRS based on EELIAU ([ΔZAU low-PEEP/EELIAU low-PEEP]/[ΔZAU high-PEEP/EELIAU high-PEEP]) exhibited a weak negative relationship and poor agreement with the CT method for both non-dependent and dependent regions (R2 ~ 0.3; bias of 3.11 and 2.08, and limits of agreement of - 2.13 to 8.34 and from - 1.49 to 5.64, respectively). Changes in DRRS during a PEEP trial in ARDS patients could be monitored using EIT, based on changes in ΔZmL/EELIml and ∆ZAU. The relative change ∆ZAU offers the advantage of not requiring CT data for calibration.

Brito R ，Morais CCA ，Lazo MT ，Guiñez DV ，Gajardo AIJ ，Arellano DH ，Amato MBP ，Cornejo RA ... -  《CRITICAL CARE》

Dynamic Relative Regional Lung Strain Estimated by Electrical Impedance Tomography in an Experimental Model of ARDS.

To analyze the role of PEEP on dynamic relative regional strain (DRRS) in a model of ARDS, respective maps were generated by electrical impedance tomography (EIT). Eight ARDS pigs submitted to PEEP steps of 0, 5, 10, and 15 cm H2O at fixed ventilation were evaluated by EIT images. DRRS was calculated as (VT-EIT/EELI)/(VT-EIT[15PEEP]/EELI[15PEEP]), where the tidal volume (VT)-EIT and end-expiratory lung impedance (EELI) are the tidal and end-expiratory change in lung impedance, respectively. The measurement at 15 PEEP was taken as reference (end-expiratory transpulmonary pressure > 0 cm H2O). The relationship between EIT variables (center of ventilation, EELI, and DRRS) and airway pressures was assessed with mixed-effects models using EIT measurements as dependent variables and PEEP as fixed-effect variable. At constant ventilation, respiratory compliance increased progressively with PEEP (lowest value at zero PEEP 10 ± 3 mL/cm H2O and highest value at 15 PEEP 16 ± 6 mL/cm H2O; P < .001), whereas driving pressure decreased with PEEP (highest value at zero PEEP 34 ± 6 cm H2O and lowest value at 15 PEEP 21 ± 4 cm H2O; P < .001). The mixed-effect regression models showed that the center of ventilation moved to dorsal lung areas with a slope of 1.81 (1.44-2.18) % points by each cm H2O of PEEP; P < .001. EELI increased with a slope of 0.05 (0.02-0.07) (arbitrary units) for each cm H2O of PEEP; P < .001. DRRS maps showed that local strain in ventral lung areas decreased with a slope of -0.02 (-0.24 to 0.15) with each cm H2O increase of PEEP; P < .001. EIT-derived DRRS maps showed high strain in ventral lung zones at low levels of PEEP. The findings suggest overdistention of the baby lung.

Gogniat E ，Madorno M ，Rodriguez PO ，Dianti J ，Otero PE ，Krukewitt L ，Böhm SH ，Roman ES ，Tusman G ... -  《-》

Assessment of electrical impedance tomography to set optimal positive end-expiratory pressure for veno-venous ECMO-treated severe ARDS patients.

Ultra-protective ventilation with low tidal volume is used in severe acute respiratory distress syndrome (ARDS) patients under extracorporeal membrane oxygenation (ECMO). However, the optimal positive end-expiratory pressure (PEEP) is unknown. The aim of our study was to assess electrical impedance tomography's (EIT) ability to choose the best PEEP for these patients. A recruitment maneuver and after a decremental PEEP trial from 20 to 5 cmH20 were monitored by EIT, with lung images divided into four ventral-to-dorsal horizontal regions of interest. For each patient, three EIT-based PEEP were defined: PEEP ODCLmin (lowest pressure with the least EIT-based collapse lung [CL] and overdistension [OD]), PEEP ODCL15 (lowest pressure able to limit EIT-based collapse to less than or equal to 15% with the least overdistension) and PEEP Comp (PEEP with the highest EIT-based compliance). High PEEP levels were significantly associated with more overdistension while decreasing PEEP led to more collapsed zones. PEEP ODCL15 and PEEP Comp were in complete agreement with the reference Pulmonary PEEP (chosen according to usual respiratory clinical and ultrasound criteria), PEEP ODCLmin was in average agreement with the Pulmonary PEEP. EIT may be a useful real-time monitoring technique to optimize the PEEP level in severe ARDS patients under ECMO. Ultra-protective ventilation with low tidal volume is used in severe acute respiratory distress syndrome patients under extracorporeal membrane oxygenation (ECMO), but the optimal positive end-expiratory pressure is unknown. This trial shows that electrical impedance tomography may be an interesting non-invasive bedside tool to provide real-time monitoring of PEEP impact in severe ARDS patients under ECMO. The Pulmovista® electrical impedance tomography was provided by Dräger (Lübeck, Germany) during the study period. Dräger had no role in the study design, collection, analysis and interpretation of the data, writing the article, or the decision to submit the article for publication.

Puel F ，Crognier L ，Soulé C ，Vardon-Bounes F ，Ruiz S ，Seguin T ，Fourcade O ，Minville V ，Conil JM ，Georges B ... -  《-》

Electrical impedance tomography for titration of positive end-expiratory pressure in acute respiratory distress syndrome patients with chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) is one of most common comorbidities in acute respiratory distress syndrome (ARDS). There are few specific studies on the appropriate ventilation strategy for patients with ARDS comorbid with COPD, especially regarding on positive end-expiratory pressure (PEEP) titration. To compare the respiratory mechanics in mechanical ventilated ARDS patients with or without COPD and to determine whether titration of PEEP based on electrical impedance tomography (EIT) is superior to the ARDSnet protocol. This is a single center, perspective, repeated measure study. ARDS patients requiring mechanical ventilation who were admitted to the intensive care unit between August 2017 and December 2020 were included. ARDS patients were divided according to whether they had COPD into a COPD group and a non-COPD group. Respiratory mechanics, gas exchange, and hemodynamics during ventilation were compared between the groups according to whether the PEEP level was titrated by EIT or the ARDSnet protocol. A total of twenty-seven ARDS patients including 14 comorbid with and 13 without COPD who met the study eligibility criteria were recruited. The PEEP levels titrated by EIT and the ARDSnet protocol were lower in the COPD group than in the non-COPD group (6.93 ± 1.69 cm H2O vs. 12.15 ± 2.40 cm H2O, P < 0.001 and 10.43 ± 1.20 cm H2O vs. 14.0 ± 3.0 cm H2O, P < 0.001, respectively). In the COPD group, the PEEP level titrated by EIT was lower than that titrated by the ARDSnet protocol (6.93 ± 1.69 cm H2O vs. 10.43 ± 1.20 cm H2O, P < 0.001), as was the global inhomogeneity (GI) index (0.397 ± 0.040 vs. 0.446 ± 0.052, P = 0.001), plateau airway pressure (16.50 ± 4.35 cm H2O vs. 20.93 ± 5.37 cm H2O, P = 0.001), dead space ventilation ratio (48.29 ± 6.78% vs. 55.14 ± 8.85%, P < 0.001), ventilation ratio (1.63 ± 0.33 vs. 1.87 ± 0.33, P < 0.001), and mechanical power (13.92 ± 2.18 J/min vs. 15.87 ± 2.53 J/min, P < 0.001). The cardiac index was higher when PEEP was treated by EIT than when it was titrated by the ARDSnet protocol (3.41 ± 0.50 L/min/m2 vs. 3.02 ± 0.43 L/min/m2, P < 0.001), as was oxygen delivery (466.40 ± 71.08 mL/min/m2 vs. 411.10 ± 69.71 mL/min/m2, P = 0.001). Titrated PEEP levels were lower in patients with ARDS with COPD than in ARDS patients without COPD. In ARDS patient comorbid with COPD, application of PEEP titrated by EIT was lower than those titrated by the ARDSnet protocol, which contributed to improvements in the ventilation ratio, mechanical energy, cardiac index, and oxygen delivery with less of an adverse impact on hemodynamics.

Liu X ，Liu X ，Meng J ，Liu D ，Huang Y ，Sang L ，Xu Y ，Xu Z ，He W ，Chen S ，Zhang R ，Liu X ，Li Y ... -  《CRITICAL CARE》

Estimation of changes in cyclic lung strain by electrical impedance tomography: Proof-of-concept study.

Cyclic strain may be a determinant of ventilator-induced lung injury. The standard for strain assessment is the computed tomography (CT), which does not allow continuous monitoring and exposes to radiation. Electrical impedance tomography (EIT) is able to monitor changes in regional lung ventilation. In addition, there is a correlation between mechanical deformation of materials and detectable changes in its electrical impedance, making EIT a potential surrogate for cyclic lung strain measured by CT (StrainCT ). To compare the global StrainCT with the change in electrical impedance (ΔZ). Acute respiratory distress syndrome patients under mechanical ventilation (VT 6 mL/kg ideal body weight with positive end-expiratory pressure 5 [PEEP 5] and best PEEP according to EIT) underwent whole-lung CT at end-inspiration and end-expiration. Biomechanical analysis was used to construct 3D maps and determine StrainCT at different levels of PEEP. CT and EIT acquisitions were performed simultaneously. Multilevel analysis was employed to determine the causal association between StrainCT and ΔZ. Linear regression models were used to predict the change in lung StrainCT between different PEEP levels based on the change in ΔZ. StrainCT was positively and independently associated with ΔZ at global level (P < .01). Furthermore, the change in StrainCT (between PEEP 5 and Best PEEP) was accurately predicted by the change in ΔZ (R2 0.855, P < .001 at global level) with a high agreement between predicted and measured StrainCT . The change in electrical impedance may provide a noninvasive assessment of global cyclic strain, without radiation at bedside.

Cornejo R ，Iturrieta P ，Olegário TMM ，Kajiyama C ，Arellano D ，Guiñez D ，Cerda MA ，Brito R ，Gajardo AIJ ，Lazo M ，López L ，Morais CCA ，González S ，Zavala M ，Rojas V ，Medel JN ，Hurtado DE ，Bruhn A ，Ramos C ，Estuardo N ... -  《-》