Open Access

Methodology of electrical impedance tomography-derived measures of regional lung ventilation

Critical Care201418:635

https://doi.org/10.1186/s13054-014-0635-5

Published: 18 November 2014

Abstract

No abstract

In the previous issue of Critical Care, we read with interest the article by Blankman and colleagues [1], who studied the performance of various electrical impedance tomography (EIT)-derived measures in detecting the `best’ positive end-expiratory pressure. The aim of that study is relevant; however, the article contains some methodological inaccuracies that need to be clarified.

One of the EIT measures used to characterize ventilation distribution is the center of ventilation (COV), first introduced in [2]. The authors refer appropriately to an article that contains a methodological figure illustrating how COV is derived from EIT ventilation images [3]. However, the authors incorrectly state that COV is the ratio between the EIT-derived ventilations in the dorsal and whole-image regions, provide a wrong equation 6, and attribute it to [3].

It is important for the understanding of EIT findings to appreciate that Figure one [1] does not show images of `impedance’ and the degree of `aeration’ (legend) but of tidal impedance differences representing regional tidal volumes. Regional ventilation delay (RVD) was analyzed not in [4], but in [5], where it was calculated in each pixel. A two-dimensional map was produced from these values, and standard deviation was calculated as an aggregate measure of ventilation homogeneity. Equation 3 regarding RVD calculation was used in [5], not in [6], where an additional multiplication by maximum impedance amplitude of the studied low-flow inflation was included. It is not clear which percentages of regional compliance are presented in Figure two B [1].

EIT is currently at an important stage of its development. Its clinical use might be fostered by implementation of accurate analysis tools.

Abbreviations

COV: 

Center of ventilation

EIT: 

Electrical impedance tomography

RVD: 

Regional ventilation delay

Declarations

Authors’ Affiliations

(1)
Department of Anaesthesiology and Intensive Care Medicine, University Medical Centre Schleswig-Holstein

References

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Copyright

© Frerichs et al.; licensee BioMed Central Ltd. 2014

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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