Adequate blood oxygenation and ventilation/perfusion matching should be the main goal of anaesthetic and intensive care management. At present, the sole method of improving gas exchange restricted by ventilation/perfusion mismatching is independent ventilation with two ventilators. Recently, however, a unique device has been developed, enabling ventilation of independent lungs in 1:1, 2:1, 3:1, and 5:1 proportions. The main goal of the study was to evaluate the device's utility, precision and impact on biomechanical lung parameters during thoracic surgery under general anaesthesia with double lumen tube intubation. Secondly- to measure the gas distribution in supine and lateral decubitus position.