Three broad classifications of acute respiratory failure etiologies based on regional ventilation and perfusion by electrical impedance tomography: a hypothesis-generating study

Abstract

Background: The aim of this study was to validate whether regional ventilation and perfusion data measured by electrical impedance tomography (EIT) with saline bolus could discriminate three broad acute respiratory failure (ARF) etiologies.

Methods: Perfusion image was generated from EIT-based impedance-time curves caused by 10 ml 10% NaCl injection during a respiratory hold. Ventilation image was captured before the breath holding period under regular mechanical ventilation. DeadSpace%, Shunt% and VQMatch% were calculated based on lung perfusion and ventilation images. Ventilation and perfusion maps were divided into four cross-quadrants (lower left and right, upper left and right). Regional distribution defects of each quadrant were scored as 0 (distribution% ≥ 15%), 1 (15% > distribution% ≥ 10%) and 2 (distribution% < 10%). Data percentile distributions in the control group and clinical simplicity were taken into consideration when defining the scores. Overall defect scores (DefectV, DefectQ and DefectV+Q) were the sum of four cross-quadrants of the corresponding images.

Results: A total of 108 ICU patients were prospectively included: 93 with ARF and 15 without as a control. PaO2/FiO2 was significantly correlated with VQMatch% (r = 0.324, P = 0.001). Three broad etiologies of ARF were identified based on clinical judgment: pulmonary embolism-related disease (PED, n = 14); diffuse lung involvement disease (DLD, n = 21) and focal lung involvement disease (FLD, n = 58). The PED group had a significantly higher DeadSpace% [40(24)% vs. 14(15)%, PED group vs. the rest of the subjects; median(interquartile range); P < 0.0001] and DefectQ score than the other groups [1(1) vs. 0(1), PED vs. the rest; P < 0.0001]. The DLD group had a significantly lower DefectV+Q score than the PED and FLD groups [0(1) vs. 2.5(2) vs. 3(3), DLD vs. PED vs. FLD; P < 0.0001]. The FLD group had a significantly higher DefectV score than the other groups [2(2) vs. 0(1), FLD vs. the rest; P < 0.0001]. The area under the receiver operating characteristic (AUC) for using DeadSpace% to identify PED was 0.894 in all ARF patients. The AUC for using the DefectV+Q score to identify DLD was 0.893. The AUC for using the DefectV score to identify FLD was 0.832.

Conclusions: Our study showed that it was feasible to characterize three broad etiologies of ARF with EIT-based regional ventilation and perfusion. Further study is required to validate clinical applicability of this method. Trial registration clinicaltrials, NCT04081142. Registered 9 September 2019-retrospectively registered, https://ichgcp.net/clinical-trials-registry/NCT04081142 .

Keywords: Acute respiratory failure; Electrical impedance tomography; Lung perfusion; Lung ventilation; V/Q.

Conflict of interest statement

Zhanqi Zhao receives a consulting fee from Dräger Medical. Inéz Frerichs reports funding from the European Union’s Framework Programme for Research and Innovation Horizon 2020 (WELMO, Grant No. 825572) and reimbursement of speaking fees, congress and travel costs by Dräger Medical. Other authors declare no conflict of interest.

© 2021. The Author(s).

Figures

Fig. 1

Flow chart of the enrolled patients. The control group was postoperative ICU patients without acute respiratory failure; ARF: acute respiratory failure; PED group: patients with pulmonary embolism-related disease; DLD group: patients with diffuse lung involvement disease; FLD group: patients with focal lung involvement disease; CTPA: CT pulmonary angiography

Fig. 2

Comparisons of defect scores for ventilation (middle), perfusion (right) and combined (left) in the four groups. The control group was postoperative ICU patients without acute respiratory failure; PED group: patients with pulmonary embolism-related disease; DLD group: patients with diffuse lung involvement disease; FLD group: patients with focal lung involvement disease. The boxes mark the quartiles with median marked red, while the whiskers extend from the box out to the most extreme data value within 1.5 * the interquartile range of the sample. The red crosses are outliers. *P < 0.05

Fig. 3

Comparisons of Shunt%, DeadSpace%, VQMatch% in the four groups. The control group was postoperative ICU patients without acute respiratory failure; PED group: patients with pulmonary embolism-related disease; DLD group: patients with diffuse lung involvement disease; FLD group: patients with focal lung involvement disease. The boxes mark the quartiles with median marked red, while the whiskers extend from the box out to the most extreme data value within 1.5 * the interquartile range of the sample. The red crosses are outliers.*P < 0.05

Fig. 4

Phenotype of ventilation/perfusion and individual images by EIT for the three broad ARF etiologies. The control group was postoperative ICU patients without acute respiratory failure; PED group: patients with pulmonary embolism-related disease; DLD group: patients with diffuse lung involvement disease; FLD group: patients with focal lung involvement disease. A Patient from the PED group (CTPA: demonstrated large embolism in both left and right main pulmonary arteries. Ventilation image: upper right (UR) 25%, upper left (UL) 11%, lower right (LR) 36%, lower left (LL) 28% (% denoted the ventilation distribution), DefectV score was 1. Low ventilated regions are marked in dark blue and high ventilated regions in light blue to white. Perfusion image: upper right (UR) 11%, upper left (UL) 17%, lower right (LR) 30%, lower left (LL) 43%, DefectQ score was 1. Regions with high perfusion are marked in red and low perfusion in green. V/Q match image: percentage of Shunt% area in red was 10% of the lung regions, DeadSpace% area in grey 46%, and VQMatch% region in yellow 43%. (partially adapted from our recent case report [47]). B A patient with ground glass opacity from the DLD group (CT: diffuse opacities in both lungs. Ventilation image: UR 2%, UL 19%, LR 35%, LL 23%, DefectV score was 0. Perfusion image: UR 16%, UL 18%, LR 38%, LL 27%, DefectQ score was 0. V/Q match image: Shunt% 6%, DeadSpace% 15%, and VQMatch% 78% (partially adapted from our previous study with permission of the American Thoracic Society. Copyright © 2020 American Thoracic Society [16]. All rights reserved). C A patient with acute left lung atelectasis from the FLD group (ventilation image: UR 31%, UL 1%, LR 63%, LL 5%, ventilation-defect score was 4. Perfusion image: UR 20%, UL 31%, LR32%, LL 18%, DefectQ score was 0. V/Q match image: Shunt% 55%, DeadSpace% 3%, and VQMatch% 42%). D A patient from the control group. Percentage of intrapulmonary shunt area in red was 17%, dead-space fraction area in grey 5%, and VQMatch% region in yellow 78%. DefectV and DefectQ scores were 0