Increasing FIO2 Influences Accuracy of Fick-based Assessments of Cardiac Output in Cardiac Surgery Patients

Cardiac output (CO) monitoring is often required for clinical evaluation and management in critically ill patients and during anesthesia. There are many methods to measure CO. Fick-based CO estimation (Fick-CO) is one of the most commonly used methods, while thermodilution (TD-CO) is viewed as golden standard. But Fick-CO is still widely used, especially in catheterization laboratories and pediatric cardiologic department, whose patients often with congenital heart disease. Multiple studies from the 1960s find a strong correlation between TD-CO and Fick-CO. However, more recent studies reject the conclusion. Since Fick-CO is the ratio of oxygen consumption (V'O2) to the arteriovenous difference in oxygen content, many parameters are included in the Fick equation, such as V'O2, hemoglobin (Hb), arterial oxygen saturation (SaO2), mixed venous oxygen saturation (SvO2), partial pressure of arterial oxygen (PaO2), and mixed venous oxygen tension (PvO2). Any changes of each parameter may influence the accuracy of Fick-CO calculation. This may be the reason why it remains controversial whether Fick-CO and TD-CO are interchangeable or not. Although there are lots of studies comparing Fick-CO and TD-CO, discussing the impact of V'O2 on Fick-CO, how the other parameters influence the final CO estimation are rarely focused. Therefore, the purpose of this study was to assess the influence of FIO2 on PaO2, SvO2, PvO2, and the accuracy of Fick-CO in cardiac surgery patients.