Regional expiratory time constants in severe respiratory failure estimated by electrical impedance tomography: a feasibility study

Abstract

BackgroundElectrical impedance tomography (EIT) has been used to guide mechanical ventilation in ICU patients with lung collapse. Its use in patients with obstructive pulmonary diseases has been rare since obstructions could not be monitored on a regional level at the bedside. The current study therefore determines breath-by-breath regional expiratory time constants in intubated patients with chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome (ARDS).MethodsExpiratory time constants calculated from the global impedance EIT signal were compared to the pneumatic volume signals measured with an electronic pneumotachograph. EIT-derived expiratory time constants were additionally determined on a regional and pixelwise level. However, regional EIT signals on a single pixel level could in principle not be compared with similar pneumatic changes since these measurements cannot be obtained in patients. For this study, EIT measurements were conducted in 14 intubated patients (mean Simplified Acute Physiology Score II (SAPS II) 35 ± 10, mean time on invasive mechanical ventilation 36 ± 26 days) under four different positive end-expiratory pressure (PEEP) levels ranging from 10 to 17 cmH2O. Only patients with moderate-severe ARDS or COPD exacerbation were included into the study, preferentally within the first days following intubation.ResultsSpearman’s correlation coefficient for comparison between EIT-derived time constants and those from flow/volume curves was between 0.78 for tau (τ) calculated from the global impedance signal up to 0.83 for the mean of all pixelwise calculated regional impedance changes over the entire PEEP range. Furthermore, Bland-Altman analysis revealed a corresponding bias of 0.02 and 0.14 s within the limits of agreement ranging from − 0.50 to 0.65 s for the aforementioned calculation methods. In addition, exemplarily in patients with moderate-severe ARDS or COPD exacerbation, different PEEP levels were shown to have an influence on the distribution pattern of regional time constants.ConclusionsEIT-based determination of breath-by-breath regional expiratory time constants is technically feasible, reliable and valid in invasively ventilated patients with severe respiratory failure and provides a promising tool to individually adjust mechanical ventilation in response to the patterns of regional airflow obstruction.Trial registrationGerman Trial Register DRKS 00011650, registered 01/31/17.Electronic supplementary materialThe online version of this article (10.1186/s13054-018-2137-3) contains supplementary material, which is available to authorized users.

Evaluation of histamine‐provoked changes in airflow using electrical impedance tomography in horses

“…A modified Graz consensus reconstruction algorithm for electrical impedance tomography (GREIT) adapted to the horse's anatomy was used to generate EIT images for each horse representing breathing‐related regional changes of impedance (ΔZ). Additional details on the use of EIT technology and image reconstruction are reported in the literature …”

A review of electrical impedance tomography in lung applications: Theory and algorithms for absolute images

“…Individualized PEEP setting is considered useful in reducing lung damage caused by inappropriately high PEEP [151]. Recent clinical studies highlighted the potential use of EIT for ARDS in PEEP titration with or without recruitment maneuvers [152,153,154,155,156,157,158,159,160,161,162]. Lowhagen et al [152] analyzed the changes of end-expiratory lung impedance (EELI) and intratidal ventilation distribution during PEEP changes.…”

“…EIT may help to distinguish one cause from another to guide follow-up procedures [157]. Pulletz et al [154] and Karagiannidis et al [162] calculated the regional time constants, which may reflect the low respiratory system compliance and imply pronounced regional recruitment and derecruitment. Cinnella et al [156] used EIT to prove that the application of the open lung approach in early mild ARDS would improve homogeneity in lung aeration.…”

Chest electrical impedance tomography measures in neonatology and paediatrics—a survey on clinical usefulness

“…This might be related to the fact that older children are often treated for obstructive lung diseases where the utility of this measure of respiratory system mechanics might be more intuitive. In adult patients, the use of τ reg for visualising the spatial heterogeneity of regional expiration in chronic obstructive lung disease has recently been documented (Karagiannidis et al, 2018). CV as an overall measure of ventilation heterogeneity also trended to get higher scores by paediatricians which probably reflected the higher usage of this parameter in studies on regional lung function outside the NICU setting.…”