High, Low, and Minimal Flow Anaesthesia Management: Effects on Oxygen Reserve Index and Arterial Partial Oxygen Pressure

Abstract

Objective: To determine the oxygen reserve index (ORI) as a supporting parameter to the arterial partial oxygen pressure (PaO2) in blood gases in hypoxia and hyperoxia monitoring with different fresh gas flows (FGF) in patients undergoing abdominal surgery. Study design: Randomised controlled trial. Place and Duration of the Study: Department of Anaesthesiology and Reanimation, Samsun Education and Research Hospital, Turkey, from January to September 2020. Methodology: The study population of ninety patients was divided into three groups. After the high-flow period, the inspired oxygen fraction (FiO2) and flow-guided ventilation (FGF) were set to be 4 L/m and 40% in Group H (high-flow), 1 L/m and 50% in Group L (low-flow), and 0.5 L/m and 68% in Group M (minimal-flow), respectively. Results: There was a very high statistically positive correlation between PaO2 and ORI in H, L, and M groups. When using a cut-off value of 0.005 for ORI for the detection of PaO2 >100 mmHg, the area under the curve (AUC) was 0.97 (p<0.001) with a sensitivity of 94.4% and specificity of 95.3%. The AUC was detected to be 0.95 in receiver operating characteristic (ROC) analysis when the hyperoxia cut-off value of ORI was used to determine PaO2 >150 mmHg in the estimation of hyperoxia. Conclusion: ORI can be used to complement SpO2 in low-flow anaesthesia in patients undergoing abdominal surgeries, provide guidance for PaO2, give information about tissue oxygen delivery, and contribute to the individualisation of oxygen therapy, and will therefore be included in the standard monitoring in the future.