This study aims to evaluate whether guidance by the Oxygen Reserve Index (ORi) improves inspiratory oxygen fraction (FiO₂) titration compared with conventional pulse oximetry (SpO₂)-guided oxygen administration in adult patients undergoing surgery in the beach chair position.
Oxygen therapy is routinely used during general anesthesia to prevent hypoxemia; however, excessive oxygen administration may result in hyperoxia, which has been associated with adverse cardiovascular and pulmonary effects. Standard pulse oximetry may not adequately detect hyperoxia when oxygen saturation values are high.
In this prospective comparative study, patients will receive oxygen titration guided either by SpO₂ alone or by combined ORi and SpO₂ monitoring. The primary outcome is the incidence of intraoperative hyperoxemia, assessed by arterial blood gas analysis. Secondary outcomes include intraoperative oxygenation parameters and hemodynamic variables.
Adult patients aged 18 to 65 years
American Society of Anesthesiologists (ASA) physical status I-III
Scheduled for elective orthopedic surgery in the beach chair position
Body mass index (BMI) <35 kg/m²
Age <18 or ≥65 years
Finger deformities preventing the use of Oxygen Reserve Index (ORi) monitoring
Severe anemia (hemoglobin <8 g/dL)
Pregnancy
Parallel
ORi-Guided FiO₂ Titration
Other interventionInspiratory oxygen fraction (FiO₂) will be adjusted throughout surgery using combined Oxygen Reserve Index (ORi) and peripheral oxygen saturation (SpO₂) monitoring. FiO₂ will be titrated to maintain ORi values between 0.2 and 0.5, with reassessment every 2-3 minutes.
SpO₂-Guided FiO₂ Titration
Other interventionFiO₂ will be adjusted to maintain SpO₂ at or above 98% throughout surgery.
Incidence of Intraoperative Severe Hyperoxemia
Severe hyperoxemia will be defined as an arterial partial pressure of oxygen (PaO2) ≥200 mmHg, measured by arterial blood gas analysis at predefined intraoperative time points.
Mean Peripheral Oxygen Saturation (SpO2) During Surgery
Peripheral oxygen saturation (SpO2) measured continuously during surgery using standard pulse oximetry.
Mean Oxygen Reserve Index (ORi) During Surgery
Oxygen Reserve Index (ORi) values recorded intraoperatively to evaluate oxygenation status.
Mean Fraction of Inspired Oxygen (FiO₂) During Surgery
Mean fraction of inspired oxygen (FiO₂) expressed as percentage (%), averaged over the surgical period.
Mean Cerebral Oxygen Saturation Measured by Near-Infrared Spectroscopy During Surgery
Cerebral regional oxygen saturation values measured intraoperatively using near-infrared spectroscopy.
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