An EIT device with a plurality of electrodes, which can be arranged about the chest of a patient, with a control and analyzing unit for feeding electrode pairs of a set of electrodes to record a voltage or current signal as a measured signal with electrode pairs acting consecutively as the feeding electrode pair to provide a matrix of image elements. A time series of the impedance change from the sequence of reconstructed matrices over at least one inspiration and one expiration is obtained and compared to a determined time series of the mean impedance change or a time series of a measured respiration volume, by calculating for each image element a scalar value as an indicator of a deviation. The control and analyzing unit assesses and marks the corresponding image element as being non-ventilated if the indicator of the deviation meets a preset threshold value criterion.
