The aim of this randomized controlled trial is to evaluate an algorithmic approach to gradually adding pressure-supported ventilation and end-tidal positive pressure when conventional tidal volume breathing is insufficient for adequate preoxygenation. The main question it aims to answer is:

• Will the proportion of patients receiving preoxygenation increase?
• Will the duration of preoxygenation decrease?

Participants will;

• 200 patients who were planned to undergo general anesthesia for elective surgeries
• aged between 18 and 65 years
• ASA 1-2 physical status
• ETO2 <90% at the end of the 3rd minute with spontaneous tidal volume breathing

The patients were randomly assigned to one of two groups (Group TVB and Group PSV) according to a computer-generated randomisation table. In the patients included in Group TVB, the tidal volume breathing was maintained for a further two minutes. Group PSV received inspiratory pressure support of 6 cm H2O for +1 min. At the end of four minutes, patients whose ETO₂ value had not reached a minimum of 90% were randomly divided once more into two groups. One group continued with PSV, while the other was administered 4 cm H₂O PEEP in addition to PSV (Group PSV+PEEP).

When adequate preoxygenation was achieved, the duration of preoxygenation, SpO2, end-tidal carbon dioxide (ETCO2), arterial blood pressures and heart rate values were recorded. Any adverse effects such as discomfort or gastric distension were noted.

Inclusion Criteria:

• Elective surgeries general anaesthesia was planned for a patient aged 18-65 years with ASA 1-2 physical condition.

Exclusion Criteria:

• Haemodynamically unstable, preoperative oxygen support such as increased intracranial or intraocular pressure, to be operated on by thoracic surgery have conditions in which positive pressure ventilation may be indirectly harmful, BMI≥35 kg/m2, pregnant, undergoing emergency surgery and causing leakage in mask ventilation bearded male patients were not included in the study.

My first trial.