Agreement between Central and Mixed Venous Oxygen Saturation Following Cardiac Surgery

Objective: To compare oxygen saturation of blood samples simultaneously taken from superior vena cava (ScvO2) and pulmonary artery (SvO2) in the various hemodynamic conditions that occurs in the early postoperative period following cardiac surgery. Methods: Prospective, observational study in a tertiary cardiac center, 60 ICU patients included following cardiac surgery. 56 patients completed the study with three hundred measurements collected. Exclusion criteria included those with uncorrected valvular incompetence or intracardiac shunting, and frequent arrhythmia interfering with adequate cardiac output measurement. Samples taken simultaneously from the central venous catheter and the distal lumen of pulmonary artery catheter (PAC). Samples were obtained during each cardiac output measurement as requested by the attending intensivist according to his clinical judgment. Results: The correlation between SvO2 and ScvO2 was (r=0.79, p <0.001). The mean bias between SvO2 and ScvO2 was 3.8 %, and the 95% limits of agreement were (+15.8 to – 8.2%). Receiving operating characteristic curves demonstrated that an ScvO2 of 70% or greater can predict SvO2 of 70% or greater with a specificity and sensitivity of 92% and 62% respectively. Conclusion: There is poor agreement between ScvO2 and SvO2 in patients following cardiac surgery. This agreement remains poor regardless changes in cardiac index, type of surgery and type of pharmacological support. We also conclude that a cutoff value of (70% and above) in ScvO2 is a specific –but not sensitive- method to predict adequate mixed venous oxygen saturation.