Retrospective evaluation of oxygen reserve indices at different nasal oxygen flow rates in patients undergoing gastrointestinal endoscopic procedures under anesthesia

Objective: In this study, it was aimed to investigate the Oxygen Reserve Index (ORI) values at different oxygen flow rates in patients undergoing gastrointestinal endoscopic procedures under sedation and to evaluate the relationship of ORI with other oxygenation and hemodynamic parameters. Method: In this retrospective study, data of the adult patients who underwent elective gastrointestinal endoscopy under sedation by the same physician were evaluated using patient records, anesthesia monitoring forms, and the hospital information management system. ASA I–III patients aged 18 years or older with complete data were included in the study. Emergency endoscopy procedure applied individuals, pediatric patients, ASA IV–V individuals, those with advanced respiratory failure, morbid obesity, active gastrointestinal bleeding, or any change in oxygen flow rate during the procedure were excluded from the study. Demographic characteristics, comorbidities, preoperative hemoglobin/hematocrit levels, and fasting duration were obtained from patient files. Administered sedative agents, oxygen flow rates, and hemodynamic and oxygenation parameters such as ORI, SpO₂, PI, PVI, and rSO₂ recorded at monitoring intervals, as well as recovery durations, were obtained from anesthesia forms. All patients received nasal oxygen support at a maximum flow rate of 8 L/min, and only those with a constant flow rate throughout the procedure were included in the analysis. Patients were divided into three groups based on nasal oxygen flow rate: ≤4 L/min (Group I), 5–6 L/min (Group II), and 7–8 L/min (Group III). Complications such as desaturation, nausea-vomiting, and bradycardia were also analyzed. Results: In Groups II and III, ORI levels at all monitoring intervals from the 2nd minute onward were significantly higher than baseline values, while in Group I, ORI values at the 2nd, 3rd, and 4th minutes were significantly elevated compared to baseline. In intergroup comparisons, Group I exhibited lower ORI values at all observation times compared to the other two groups. The average ORI values were as follows: Group I: 0.00–0.12, Group II: 0.10–0.27, Group III: 0.30–0.54. A statistically significant positive correlation was found between ORI and SpO₂. The estimated ORI prediction time of desaturation was 31 seconds in Group I, 35 seconds in Group II, and 39 seconds in Group III. Conclusion: The findings suggest that low oxygen flow rates may be associated with an increased risk of hypoxemia, whereas high flow rates may contribute to the development of hyperoxia. Administering oxygen at a flow rate of 5–6 L/min appears to offer a safer approach by minimizing the risks of both inadequate oxygenation and oxygen overload. Further large-scale studies are warranted to substantiate these findings. Keywords: Gastrointestinal endoscopy, Oxygen Reserve Index (ORI), Nasal oxygen cannula, Non-operating room anesthesia, Sedation