Electrical impedance tomography: a valuable tool for the clinician
Keywords:electrical impedance tomography, regional ventilation monitoring, lung imaging
Electrical Impedance Tomography (EIT) is a non-invasive, easy-to-use bedside imaging technique that provides dynamic assessment of pulmonary ventilation as well as functional analysis of distinct lung regions. The impedance variations are measured by applying a low intensity alternating current (5mA, 50-70 Hz) through electrodes placed on a belt positioned at the level of the patient's ribcage. The images reconstructed on the screen are either static or dynamic and represent the conductivity distribution at a given instant or the variation of the conductivity distribution between two instants. They allow the clinician to assess in real time the degree of homogeneity of the ventilation and to detect any ventilatory asynchrony.
In practice, the TIE makes it possible to quantify the regional variations of pulmonary impedance at the end of expiration, which would be closely related to variations in end-expiration lung volume. It also offers the possibility of measuring the impedance variation at each respiratory cycle, the regional compliance of the respiratory system, evaluating the areas of collapse, atelectasis or overdistension, calculating the center of ventilation or the regional ventilation delay. It allows to monitor the ventilation in real time and continuously and to assess the impact of different mechanical ventilation settings (PEEP titration ...) or therapeutic maneuvers on the regional ventilation.