The Effectiveness of Oxygen Reserve Index in Early Detection of Desaturation in Geriatric Patients Scheduled for Oncological Surgery

This study is a prospective, observational study. Patients aged 65 years and older who are scheduled for elective oncologic surgery at Ankara Bilkent City Hospital will be included. In all patients, the Clinical Frailty Scale will be routinely assessed during the preoperative period. In this study, tolerable apnea time will be defined as the time until peripheral oxygen saturation (SpO₂), measured by pulse oximetry, decreases to 94%. Although SpO₂ values of 90% and above have been accepted in the literature, the World Health Organization defines normal SpO₂ as 95% and above and considers values of 94% and below as an indication for treatment. The Oxygen Reserve Index (ORI) ranges from 0 to 1, and the ORI alarm value triggered by the device due to a downward trend will be recorded. ORI is a dimensionless index ranging from 1 (high oxygen reserve) to 0 (no oxygen reserve), which is measured by optically detecting changes in venous oxygen saturation (SvO₂) after arterial oxygen saturation (SpO₂) reaches 100%. ORI is measured using a multi-wavelength pulse co-oximeter placed on a fingertip. In addition to routine anesthesia monitoring, including electrocardiography, pulse oximetry, and hemodynamic monitoring, patients will also be monitored using Masimo Rainbow SET® Pulse CO-Oximetry. Due to the oncologic nature of the surgeries and the associated risk of bleeding, close hemodynamic monitoring is required; therefore, invasive arterial blood pressure monitoring will be established in all patients before anesthesia induction. All patients will be preoxygenated with 100% oxygen for 3 minutes. After establishing intravenous access, anesthesia induction will be performed using intravenous propofol at a dose of 2 mg/kg and fentanyl at a dose of 1 µg/kg. Neuromuscular blockade will be achieved with rocuronium at a dose of 0.6 mg/kg. All patients will be intubated by an experienced anesthesiologist using a videolaryngoscope. Oxygen Reserve Index (ORI) and peripheral oxygen saturation (SpO₂) values will be recorded, and arterial blood gas analyses will be performed at five predefined time points: baseline (initial values), after 3 minutes of preoxygenation, after 2 minutes of bag-mask ventilation following intubation, during apnea when SpO₂ decreases to 94% without ventilation, and after 2 minutes of ventilation with 100% oxygen. ORI warning time will be defined as the interval from the onset of the ORI alarm to the decrease of SpO₂ to 94%. SpO₂ warning time will be defined as the duration of the decrease in SpO₂ from 97% to 94%.