The surgeon's satisfaction or comfort with the surgical conditions was assessed using a visual analogue scale. rSO<sub>2</sub> level, mean arterial pressure, pulse oxygen saturation, arterial blood gas analysis, intraoperative hypoxaemia, intraoperative use of CPAP during OLV, and awakening time were determined in patients at the following time points: while inhaling air (T<sub>0</sub>), after anaesthesia induction andinhaling 100% oxygen in the supine position under double lung ventilation for five mins (T<sub>1</sub>), at two mins after skin incision (T<sub>2</sub>), at ten mins after skin incision (T<sub>3</sub>), and after the lung recruitment manoeuvres and inhaling 50% oxygen for five mins (T<sub>4</sub>).