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Mapping Regional Differences of Local Pressure-Volume Curves With Electrical Impedance Tomography

Beda, Alessandro PhD; Carvalho, Alysson R. DSc; Carvalho, Nadja C. PhD; Hammermüller, Sören RN; Amato, Marcelo B. P. MD, PhD; Muders, Thomas MD; Gittel, Claudia DVM; Noreikat, Katharina DVM; Wrigge, Hermann MD, PhD; Reske, Andreas W. MD, PhD

doi: 10.1097/CCM.0000000000002233
Laboratory Investigations

Objectives: Lung-protective mechanical ventilation aims to prevent alveolar collapse and overdistension, but reliable bedside methods to quantify them are lacking. We propose a quantitative descriptor of the shape of local pressure-volume curves derived from electrical impedance tomography, for computing maps that highlight the presence and location of regions of presumed tidal recruitment (i.e., elastance decrease during inflation, pressure-volume curve with upward curvature) or overdistension (i.e., elastance increase during inflation, downward curvature).

Design: Secondary analysis of experimental cohort study.

Setting: University research facility.

Subjects: Twelve mechanically ventilated pigs.

Interventions: After induction of acute respiratory distress syndrome by hydrochloric acid instillation, animals underwent a decremental positive end-expiratory pressure titration (steps of 2 cm H2O starting from ≥ 26 cm H2O).

Measurements and Main Results: Electrical impedance tomography-derived maps were computed at each positive end-expiratory pressure-titration step, and whole-lung CT taken every second steps. Airway flow and pressure were recorded to compute driving pressure and elastance. Significant correlations between electrical impedance tomography-derived maps and positive end-expiratory pressure indicate that, expectedly, tidal recruitment increases in dependent regions with decreasing positive end-expiratory pressure (p < 0.001) and suggest that overdistension increases both at high and low positive end-expiratory pressures in nondependent regions (p < 0.027), supporting the idea of two different scenarios of overdistension occurrence. Significant correlations with CT measurements were observed: electrical impedance tomography-derived tidal recruitment with poorly aerated regions (r = 0.43; p < 0.001); electrical impedance tomography-derived overdistension with nonaerated regions at lower positive end-expiratory pressures and with hyperaerated regions at higher positive end-expiratory pressures (r ≥ 0.72; p < 0.003). Even for positive end-expiratory pressure levels minimizing global elastance and driving pressure, electrical impedance tomography-derived maps showed nonnegligible regions of presumed overdistension and tidal recruitment.

Conclusions: Electrical impedance tomography-derived maps of pressure-volume curve shapes allow to detect regions in which elastance changes during inflation. This could promote individualized mechanical ventilation by minimizing the probability of local tidal recruitment and/or overdistension. Electrical impedance tomography-derived maps might become clinically feasible and relevant, being simpler than currently available alternative approaches.

1Department of Electronic Engineering, BioSiX—Biomedical Signal Processing, Analysis and Simulation Group, Postgraduate Program of Electrical Engineering (PPGEE), Federal University of Minas Gerais, Belo Horizonte, Brazil.

2Department of Physiology, Laboratory of Respiration Physiology, Carlos Chagas Filho Institute of Biophysics, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.

3Laboratory of Pulmonary Engineering, Biomedical Engineering Program, Alberto Luis Coimbra Institute of Post-Graduation and Research in Engineering; Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.

4Pulmonary Division, Cardio-Pulmonary Department, Heart Institute (InCor), University of São Paulo, São Paulo, Brazil.

5Department of Anesthesiology and Intensive Care Medicine, University Hospital Leipzig, Leipzig, Germany.

6Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Bonn, Germany.

7Large Animal Clinic for Surgery, Faculty of Veterinary Medicine, University of Leipzig, Leipzig, Germany.

The experiments were performed in the animal research lab of the Large Animal Clinic for Surgery, Faculty of Veterinary Medicine, University of Leipzig, Leipzig, Germany. The analysis of the data was performed at the Department of Electronic Engineering of the Federal University of Minas Gerais, Belo Horizonte, Brazil.

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Drs. Beda and Carvalho are funded by Fundação de Amparo a Pesquisa do Estado de Minas Gerais, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, and Conselho Nacional de Desenvolvimento Científico e Tecnológico (Brazil).

Dr. Beda disclosed other support in the form of scholarships and funding for his research activities (not specifically linked to a research project) from Fundação de Amparo a Pesquisa do Estado de Minas Gerais (Brazil), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil). Dr. Carvalho received support for article research from CAPES, CNPq, and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro, Brazil. Dr. Hammermüller received funding from part time work (50%) as an application specialist for Swisstom, Landquart, Switzerland. Dr. Wrigge disclosed that he received speaker honoraria from GE Healthcare, Maquet, Pulsion, MSD, Dräger Medical, Infectopharm; institution received funding from the German Research Foundation (DFG grant WR 47/1-1) and Dräger Medical, Lübeck, Germany (unrestricted grant). Dr. Reske received support for article research from Howard Hughes Medical Institute. The remaining authors have disclosed that they do not have any potential conflicts of interest.

For information regarding this article, E-mail: ale.beda@gmail.com

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