Oxygen Reserve Index

Oxygen administration is essential in the perioperative period to prevent hypoxia; however, excessive oxygen may cause hyperoxia and related complications. While pulse oximetry is effective in detecting hypoxemia, it is insufficient for identifying hyperoxia when SpO₂ exceeds 97%, often necessitating invasive arterial blood gas analysis. The Oxygen Reserve Index (ORI) is a noninvasive, real-time monitoring parameter reflecting moderate hyperoxic ranges (PaO₂ 100-200 mmHg) and provides early warning of oxygenation changes before SpO₂ alterations occur. Combined use of ORI and pulse oximetry may enable optimal oxygen titration and prevention of both hypoxemia and hyperoxemia. Laparoscopic nephrectomy is widely performed due to its clinical advantages. In our practice, low and normal fresh gas flow anesthesia are commonly used. Low-flow anesthesia offers benefits such as preservation of heat and humidity, reduced cost, and improved airway physiology. This study aims to determine optimal oxygenation levels during laparoscopic nephrectomy under low and normal fresh gas flow conditions using ORI monitoring.

This randomized clinical trial investigates whether Oxygen Reserve Index (ORi) monitoring enables earlier detection of impending hypoxemia compared with conventional pulse oximetry during apneic intermittent ventilation in adult patients undergoing endolaryngeal surgery under general anesthesia. By providing continuous, noninvasive assessment of oxygen reserve in the hyperoxic range, ORi may offer an earlier warning of oxygen depletion before peripheral oxygen saturation declines. The study compares time to reventilation thresholds, arterial blood gas parameters, and perioperative respiratory outcomes between ORi-guided and standard SpO₂-guided monitoring strategies.

Atelectasis is a frequent pulmonary complication after general anesthesia, often triggered by preoxygenation and intraoperative hyperoxia. High inspiratory oxygen fractions (FiO₂) can promote absorption atelectasis, ventilation-perfusion mismatch, hemodynamic alterations, and oxidative injury. This study evaluates the effect of two intraoperative oxygen management strategies-oxygen reserve index (ORI)-guided FiO₂ titration versus fixed 50% FiO₂-on postoperative atelectasis in patients undergoing thoracolumbar spine surgery under general anesthesia. Atelectasis severity will be assessed using lung ultrasonography (LUS), scored across 12 thoracic regions (0-3 per region, total 0-36), while respiratory function changes will be examined via preoperative and 24-hour postoperative spirometry (FVC, FEV₁, FEV₁/FVC). Because postoperative spirometry may be influenced by pain, Numeric Rating Scale (NRS) scores will be recorded to help distinguish true restrictive patterns from pain-limited respiratory effort. The study aims to determine whether ORI-guided FiO₂ titration can reduce postoperative atelectasis and improve respiratory outcomes compared with a fixed FiO₂ approach.

This prospective observational study aims to evaluate the relationship between the Oxygen Reserve Index (ORI) and tolerable apnea time in geriatric patients undergoing elective oncologic surgery under general anesthesia. Patients aged 65 years and older will be monitored using standard anesthesia monitoring and Masimo Rainbow SET® Pulse CO-Oximetry during anesthesia induction and tracheal intubation. Tolerable apnea time will be defined as the duration from the end of ventilation after intubation to a decrease in peripheral oxygen saturation (SpO₂) to 94%. The primary objective is to assess the association between ORI warning time and tolerable apnea time. Secondary objectives include evaluating the association between ORI values, arterial blood gas parameters at predefined time points, and the Clinical Frailty Scale.

Background: The Oxygen Reserve Index (ORI) is a non-invasive parameter utilizing multi-wavelength pulse co-oximetry. ORI can provide early warnings of deteriorating oxygenation before changes are reflected in SpO₂ levels. This study aimed to investigate the feasibility of non-ventilated intubation in patients undergoing cholecystectomy as a means to achieve safe intubation without nasogastric tube placement, with reduced trauma and cost, and improved time efficiency.

The purpose of this study is to compare the time required to reach an end-tidal oxygen (EtO2) value of 90% and the time until the Oxygen Reserve Index (ORI) drops below 0.55 during preoxygenation in sarcopenic and non-sarcopenic patients. The study aims to investigate the impact of sarcopenia on the oxygenation process.