Variations in oxygen reserve index in different fresh gas flow rates

Background: The Oxygen Reserve Index (ORI) is a real-time monitoring measure associated with oxygen reserve status in the moderate hyperoxic range (arterial oxygen tensionapproximately 100–200 mmHg). In this study, our primary objective was to determine whether ORI can be a reliable and sensitive indicator of hypoxia in minimal-flow anesthesia (MFA) settings. Methods: This randomized controlled trial included 64 patients who were randomized into two groups: Group M (minimal flow anesthesia group) and Group H (high flow anesthesia group). The subjects were American Society of Anesthesiologists (ASA) I–III patients aged 18–75 who underwent elective ear, nose and throat surgery lasting longer than 60 min under general anesthesia. In Group H, a fresh gas flow (FGF) of 4 L/min was used, while in Group M, a FGF of 0.5 L/min was administered. ORI monitoring was performed on all patients. Results: Both groups were comparable in terms of height, weight, ASA classification, surgery and anesthesia durations, preoperative hemoglobin and the saturation of peripheral oxygen (SpO2) and basal ORI levels. ORI values were similar between the groups during preoxygenation, after intubation, and at 5 min post-intubation. Statistically significant differences favoring in favor of Group M were observed at 10 min, 15 min, 20 min and 35 min. End-tidal O2 values at intubation and 5 min post-intubation were similar; however, significant differences were found at 10, 15, 20 and 35 min post-intubation, and after increasing fresh gas flow. Conclusions: The ORI values can help detect impending desaturation before changes in SpO2 are evident. Our findings suggest that ORI monitoring during low-flow anesthesia application can be valuable in avoiding hypoxia, thereby supporting the application of low-flow anesthesia techniques. Clinical Trial Registration: Clinical trials ID: NCT06649279.

Oxygen reserve index; Minimal flow; High flow; Hypoxia; Hyperoxia; Anesthesia

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