title: Imbalances in regional lung ventilation: a validation study on electrical impedance tomography.
abstract: Imbalances in regional lung ventilation, with gravity-dependent collapse and overdistention of nondependent zones, are likely associated to ventilator-induced lung injury. Electric impedance tomography is a new imaging technique that is potentially capable of monitoring those imbalances. The aim of this study was to validate electrical impedance tomography measurements of ventilation distribution, by comparison with dynamic computerized tomography in a heterogeneous population of critically ill patients under mechanical ventilation. Multiple scans with both devices were collected during slow-inflation breaths. Six repeated breaths were monitored by impedance tomography, showing acceptable reproducibility. We observed acceptable agreement between both technologies in detecting right-left ventilation imbalances (bias = 0% and limits of agreement = -10 to +10%). Relative distribution of ventilation into regions or layers representing one-fourth of the thoracic section could also be assessed with good precision. Depending on electrode positioning, impedance tomography slightly overestimated ventilation imbalances along gravitational axis. Ventilation was gravitationally dependent in all patients, with some transient blockages in dependent regions synchronously detected by both scanning techniques. Among variables derived from computerized tomography, changes in absolute air content best explained the integral of impedance changes inside regions of interest (r(2) > or = 0.92). Impedance tomography can reliably assess ventilation distribution during mechanical ventilation.
authors.affiliation: Respiratory ICU, Hospital das Clinicas, Pulmonary Department, Univerisity of São Paulo, São Paulo, Brazil.
authors.forename: Josué A
authors.initials: JA
authors.lastname: Victorino
authors.forename: João B
authors.initials: JB
authors.lastname: Borges
authors.forename: Valdelis N
authors.initials: VN
authors.lastname: Okamoto
authors.forename: Gustavo F J
authors.initials: GF
authors.lastname: Matos
authors.forename: Mauro R
authors.initials: MR
authors.lastname: Tucci
authors.forename: Maria P R
authors.initials: MP
authors.lastname: Caramez
authors.forename: Harki
authors.initials: H
authors.lastname: Tanaka
authors.forename: Fernando Suarez
authors.initials: FS
authors.lastname: Sipmann
authors.forename: Durval C B
authors.initials: DC
authors.lastname: Santos
authors.forename: Carmen S V
authors.initials: CS
authors.lastname: Barbas
authors.forename: Carlos R R
authors.initials: CR
authors.lastname: Carvalho
authors.forename: Marcelo B P
authors.initials: MB
authors.lastname: Amato
mesh_terms: D000328:Adult; D017097:Electric Impedance; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods*; D012123:Pulmonary Ventilation; D015203:Reproducibility of Results; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000628:therapy; D015656:Respiratory Mechanics; D012815:Signal Processing, Computer-Assisted; D014054:Tomography / Q000379:methods*; D014057:Tomography, X-Ray Computed