NEW YORK (Reuters Health) - Bedside electrical impedance tomography (EIT) can be used to evaluate lung ventilation distribution during mechanical ventilation, according to a report from Brazil. The results seem reliable enough to make clinical adjustments.
MRI and CT can reveal lung heterogeneities, the authors explain in the April 1st American Journal of Respiratory and Critical Care Medicine, but they are unsuitable for bedside monitoring in intensive care settings.
In their introduction, Dr. Marcelo B. P. Amato from University of Sao Paulo and colleagues note that EIT is based on measurements of electrical potentials at the chest wall surface. “Within a particular cross-sectional plane, harmless electrical currents are driven across the thorax in a rotating pattern, generating a potential gradient at the surface, which is then transformed into a two-dimensional image of the electrical impedance distribution within the thorax.”
Based on experimental studies suggesting that EIT is very sensitive to regional changes in lung aeration, the investigators compared EIT measurements of ventilation distribution in a heterogeneous population of critically ill patients receiving mechanical ventilation with those obtained by dynamic computerized tomography.
Within-subject variability of EIT results (as measured by standard deviation between repeated measures) was well below the a priori reproducibility cutoff of 9%, the authors report, and all estimates of regional volume distribution showed acceptable agreement with CT results.
EIT measures of right/left imbalances in regional lung ventilation were most precise, the researchers note, yet gravity-related imbalances in regional lung ventilation could still be reliably estimated.
“We think that the reported performance of EIT was good enough for certain clinical applications, especially bedside adjustments of mechanical ventilation with immediate feedback,” the authors conclude. “Even at its current stage of development, EIT can reliably assess imbalances in distribution of lung ventilation in critically ill patients.”
“A bedside tool for the adjustment of mechanical ventilation with the capacity of measuring regional ventilation and perfusion would be worth waiting for,” writes Dr. Goran Hedenstierna from University Hospital, Uppsala, Sweden in a related editorial. “It seems like we are close to getting it.”
Source: Am J Respir Crit Care Med 2004;169:791-800,777-778. [ Google search on this article ]
MeSH Headings:Biological Sciences: Biophysics: Electric Conductivity: Electrophysiology: Physical Sciences: Physics: Physiology: Physiological Processes: Tomography: Electric Impedance: Biological Sciences: Physical SciencesCopyright © 2002 Reuters Limited. All rights reserved. Republication or redistribution of Reuters content, including by framing or similar means, is expressly prohibited without the prior written consent of Reuters. Reuters shall not be liable for any errors or delays in the content, or for any actions taken in reliance thereon. Reuters and the Reuters sphere logo are registered trademarks and trademarks of the Reuters group of companies around the world.
