Comparison of Oxygen Reserve Index and Regional Cerebral Oxygen Saturation in Determining Hypoxia in Obese Patients

Standard noninvasive monitoring will be applied to the patients taken to the operating table, and heart rate, mean arterial pressure, peripheral oxygen saturation (SpO2), oxygen reserve index (ORI), regional cerebral oxygen saturation, etCO2 values will be recorded. Cerebral oximeter probe placed in the middle of the forehead (every second Cerebral oxygen saturation will be continuously monitored using a rcSO2 reading) (Massimo)Preoxygenation will be performed until the expiratory O2 concentration is 90% (during spontaneous ventilation, FIO2 will be kept between 100% 6 lt7min flow rate and EtCO2 30-35 mmHg). 2 mg midazolam, 2 ug General anesthesia with /kg fentanyl, 3 mg/kg propofol, 0.6 mg/kg rocuronium and 100% O2 will be applied and intubated with a videolaryngoscope. The breathing circuit will be disconnected from the endotracheal tube until the SpO2 drops to 94%. At that time, the breathing circuit will be connected and the patients will be ventilated with 100% FiO2, 8 ml kg-1 ideal body weight, targeted tidal volume, and 5 cm H2O positive end-expiratory pressure until the ORI plateaus. Throughout this process, ORI and cerebral oxygen saturation will be recorded continuously. ORI and rcO2 data will be compared at seven specific time points ( (1) during the basal period; (2) at the end of preoxygenation when ORI reaches a plateau; (3) at the beginning of intubation; (4) when SpO2 reaches 97%; (5) when SpO2 reaches 94% (6) ORI reaches a plateau again (during ventilation with 100% FiO2), and (7) SpO2 reaches baseline