Clinical applications of electrical impedance tomography in the monitoring of changes in intrathoracic fluid volumes.

We have previously shown that EIT can detect changes in intrathoracic fluid volumes in normal subjects undergoing a fluid challenge. We now report the preliminary results of two studies designed to investigate the ability of EIT to monitor changes in intrathoracic fluid in disease states. All recordings were made using the Sheffield Mark 1 system with the 16 electrode array placed around the lower thorax. Ten patients were studied during the sequential aspiration of unilateral pleural effusions. Following recording of a baseline dataset during tidal breathing (600 cycles) fluid was aspirated in 300 ml aliquots up to a maximum of 1000 ml, 600 cycles of data being collected after each aspiration. On the side of the effusion there was a progressive increase in intrathoracic resistivity in all patients as the fluid was aspirated. The mean increase in resistivity per 100 ml aspirated was 7%, range 3%-13%, p < 0.01 pre- versus post-aspiration resistivity. In the contralateral lung there was a smaller increase in all subjects (mean 1.8%, range 1%-3%) consistent with a reduction in mediastinal shift following aspiration. In these preliminary observations we have shown that EIT can be used in the clinical environment to detect small changes in intrathoracic fluid.