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Computed tomography (CT) in patients with acute respiratory distress syndrome has shown that intrapulmonary gas is not homogeneously distributed. Although regional ventilation can be studied by isotope and magnetic resonance techniques while aeration of the lungs can be imaged using CT, these techniques are not available at the bedside. Recently, electrical impedance tomography has been introduced as a true bedside technique which provides information on regional ventilation distribution.Electrical impedance tomography can reliably determine regional ventilation in healthy lungs and various models of induced lung injury when compared with CT, electron beam CT, and single photon emission CT. In healthy volunteers and patients with acute lung injury, relative impedance changes on the electrical impedance tomography image demonstrate an excellent correlation with regional changes in lung air content detected by CT. In a limited number of patients with respiratory dysfunction, gas exchange was found to improve when electrical impedance tomography was used to adjust ventilator settings, improving regional ventilation and avoiding tidal alveolar collapse.In view of recently published data, it can be concluded that, in critically ill patients, electrical impedance tomography determines reliable regional ventilation. Therefore, this technique has the potential to become a valuable bedside tool.