Published ahead of print on December 23, 2003, doi:10.1164/rccm.200301-133OC
Am. J. Respir. Crit. Care Med., Volume 169, Number 7, April 2004, 791-800
A more recent version of this article appeared on April 1, 2004
Submitted on February 11, 2003
Accepted on December 18, 2003
IMBALANCES IN REGIONAL LUNG VENTILATION: A VALIDATION STUDY ON ELECTRICAL IMPEDANCE TOMOGRAPHY
JOSUE A VICTORINO1, JOAO B BORGES1, VALDELIS N OKAMOTO1, GUSTAVO F.J. MATOS1, MAURO R TUCCI1, MARIA P.R. CARAMEZ2, HARKI TANAKA1, FERNANDO SUAREZ SIPMANN3, DURVAL C.B. SANTOS4, CARMEN S.V. BARBAS1, CARLOS R.R CARVALHO1, and MARCELO B.P. AMATO1*
1 Respiratory Intensive Care Unit, Pulmonary Division, Hospital das Clinicas, University of Sao Paulo, Sao Paulo, SP, Brazil,
2 General Intensive Care Unit, Emergency Clinics Division, Hospital das Clinicas, University of Sao Paulo, Sao Paulo, SP, Brazil,
3 Intensive Care, Fundacion Jimenez Diaz, Madrid, Spain,
4 Radiology, Hospital das Clinicas, University of Sao Paulo, Sao Paulo, SP, Brazil
* To whom correspondence should be addressed. E-mail: amato{at}unisys.com.br.
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 potentially capable of monitoring those imbalances. The aim of this study was to validate EIT 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 (R2  0.92). Conclusion: impedance tomography can reliably assess ventilation distribution during mechanical ventilation.
Key words: Artificial Respiration; Physiologic Monitoring; Validation Studies; Adult Respiratory Distress Syndrome; Respiratory Insufficiency
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