 By application of small currents via electrodes around the thorax and measuring of the resultant resistance the electrical impedance tomography EIT can determine the level of aeration of the lung in a cross sectional plane. The EIT device used in this study calculates the percentage of the investigated lung area that can be defined as over distended or collapsed respectively. In these sections the change of resistance within a respiration cycle is reduced compared to well ventilated areas are therefore called silent spaces. Silent spaces located ventral are termed non-dependent NSS and silent spaces located dorsal are termed dependent DSS. Based on this information the clinician is able to set the respirator in a more lung protective manor. 