Is Effective Preoxygenation in Elderly Patients Related to Position?

Patients will be randomized into 3 groups. The patients will lay in the supine position, in the control group and 20 and 30 degrees head up position in other two groups. Each patient will be preoxygenated with well fitting anaesthesia face mask with FiO2 of 100% at least 6L of flow until the ETO2 reaches concentration of 85%. The angle (20 or 30 degrees) formed by the patients' bodies (hips and feet parallel to the ground, lifting the back from the ground plane) with the ground will be measured with a spirit level, angle meter, and confirmed with a smartphone application. The time to reach ETO2 85% by starting preoxygenation in patients will be measured and recorded with a stopwatch. When the target is reached, anesthesia induction will be performed and the patients will be intubated. After the start of the intubation attempt, the stopwatch will be started again, after intubation, the patient will be ventilated with a balloon once and the location of the tube will be confirmed, the circuit will be separated and SpO2 will be expected to go down to the level of 92 % and recorded during this time.