Increased FIO2 Influences SvO2 Interpretation and Accuracy of Fick-based Cardiac Output Assessment in Cardiac Surgery Patients

Background: The study aimed to reveal how the fraction of inspired oxygen (FIO 2 ) affected the value of mixed venous oxygen saturation (SvO 2 ) and the accuracy of Fick-equation-based cardiac output (Fick-CO). Methods: Forty-two adult patients who underwent elective cardiac surgery were enrolled and randomly divided into two groups: FIO 2 <0.7 or >0.85. Under stable general anesthesia, thermodilution-derived cardiac output (TD-CO), SvO 2 , PvO 2 , hemoglobin, SaO 2 , PaO 2 , and blood pH levels were recorded before surgical incision. Results: Significant differences in FIO 2 values were observed between the two groups (0.56 ±0.08 in the <70% group and 0.92 ±0.03 in the >0.85 group; p <0.0001). The increasing FIO 2 values lead to increases in SvO 2 , PvO 2 , and PaO 2 , with little effects on cardiac output and hemoglobin levels. When comparing to TD-CO, the calculated Fick-CO in both groups had moderate Pearson correlations and similar linear regression results. Although the FIO 2 <0.7 group presented a less mean bias and a smaller limits of agreement, neither group met the percentage error criteria of <30% in Bland-Altman analysis. Conclusions: Increased FIO 2 may influence the interpretation of SvO 2 and the exacerbation of Fick-CO estimation, which could affect clinical management. Trial Registration: ClinicalTrials.gov ID number: NCT04265924. Retrospectively registered (Date of registration: February 12, 2020).