Tidal ventilation distribution in EIT images at different PEEP levels. (a) 6 mbar. (b) 14 mbar. (c) 22 mbar. The tidal images were the differences of relative impedance between end-inspiration and end-expiration in electrical impedance tomography (EIT) images. High ventilated regions are marked in red, while low ventilated regions are marked in blue. PEEP = positive end-expiratory pressure.