Bedside Replacement of Computed Tomography by Electrical Impedance Tomography

Abstract

In the adult respiratory distress syndrome (ARDS) mechanical ventilation is used to maintain adequate oxygenation, but mechanical ventilation can be hazardous to the lung itself. Different ventilation approaches have been developed to open the lung and to reduce the risk of any trauma to the alveoli during mechanical ventilation [1, 2]. However, in the vertical gradient from anterior to posterior lung density increases, indicating an increase in collapse of alveoli in this gradient due to pulmonary oedema, loss of surfactant and alveolar damage [3]. With increasing pulmonary oedema the differences in the vertical gradient are even more pronounced. The increase in lung weight due to pulmonary edema causes collapse of alveoli at the posterior site of the lungs owing to gravitational forces. Knowing whether and in what region alveoli are collapsed or open might help in the adjustment of mechanical ventilation and/or might give insight in the severity of pulmonary oedema. Therefore, regional information about the division of functional lung volume is needed. CT-scanning of the lung has already been proven useful for the assessment of the regional information [3], but is impractical at the intensive care unit (ICU) since it can not be used at the bedside. With a recent non-invasive bedside method, called Electrical Impedance Tomography (EIT), regional information about the division of functional lung volume can also be obtained. EIT registers changes in impedance due to lung volume changes in a 2-D image plane [4, 5]. In this abstract we will briefly describe the basics of EIT and some experimental results.