Evaluation of Oxygenation in Low- and High-Flow Anesthesia Applications by Oxygen Reserve Index: A Randomized Prospective Study

Abstract

Aim:While arterial blood gas (ABG) analysis is invasive, intermittent, and costly, the oxygen reserve index (ORI) is a new method that can be non-invasive and continuous measurement aimed at providing information about the patient’s O2 status in the moderately hyperoxic range. In our study, the ORI to PaO2 relationship in different fresh gas flows was evaluated.Methods:This randomized prospective study was conducted between November 2018 and November 2019. All patients were ventilated for the first 10 min after intubation with 50% O2/air and 6 L/min fresh gas flow. Then, the flow rate was randomly set to 4 L/min for high-flow anesthesia (group H) or 1 L/min for low-flow anesthesia (group L). ABG’s were taken before preoxygenation, intraoperative 60th min, and at the end of surgery, and simultaneous ORI and SpO2 were recorded.Results:The study was completed with 70 patients. Mean PaO2 values were higher in group H, apart from before preoxygenation (p<0.05). Mean ORI values differed between groups except before preoxygenation and the intraoperative 10th min (p<0.05). A statistically significant, positive and weak correlation was identified between ORI and PaO2. According to the regression analysis, the ORI value was approximately 0.2 when the PaO2 value was ≥100 mmHg at the intraoperative 60th min and at the end of the surgery, and 0.3 when the PaO2 was ≥150 mmHg.Conclusion:ORI may be an alternative to PaO2 in monitoring the oxygen status of intraoperative patients.

Keywords

• general anesthesia
• hyperoxia
• low flow anesthesia
• oxygen reserve index