Electrical impedance tomography measured at two thoracic levels can visualize the ventilation distribution changes at the bedside during a decremental positive end-expiratory lung pressure trial

Ventilation distribution was calculated on the basis of EIT results from 12 mechanically ventilated patients after cardiac surgery at a cardiothoracic ICU. Measurements were taken at four PEEP levels (15, 10, 5 and 0 cm H2O) at both the cranial and caudal lung levels, which were divided into four ventral-to-dorsal regions. Regional compliance was calculated using impedance and driving pressure data.We found that tidal impedance variation divided by tidal volume significantly decreased on caudal EIT slices, whereas this measurement increased on the cranial EIT slices. The dorsal-to-ventral impedance distribution, expressed according to the center of gravity index, decreased during the decremental PEEP trial at both EIT levels. Optimal regional compliance differed at different PEEP levels: 10 and 5 cm H2O at the cranial level and 15 and 10 cm H2O at the caudal level for the dependent and nondependent lung regions, respectively.At the bedside, EIT measured at two thoracic levels showed different behavior between the caudal and cranial lung levels during a decremental PEEP trial. These results indicate that there is probably no single optimal PEEP level for all lung regions.Electrical impedance tomography (EIT) is a promising new tool for bedside monitoring of regional lung ventilation and changes in regional and global lung volume [1-3]. EIT is a technique based on the injection of small electrical currents and voltage measurements using electrodes on the skin surface. Cross-sectional images are generated from these measurements, representing impedance change in a 5- to 10-cm-wide slice of the thorax. It is a radiation-free, noninvasive, portable lung imaging technique.EIT can be performed at different craniocaudal levels of the thoracic cage, but the caudal thoracic level just above the diaphragm is of particular importance because atelectasis due to mechanical ventilation can be expected most at this level. On the basis of computed tomography (CT), it is known that t