Abstract
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.
Highlights
Mixed venous O2 saturation (SvO2) is a clinical marker of global oxygen utilization, and it has been shown to be a surrogate for the interaction between cardiac output, arterial oxygen content and tissue oxygen uptake [1]
Patients who were excluded from the study were those with uncorrected valvular incompetence or intracardiac shunting, and patients having frequent arrhythmia interfering with adequate cardiac output measurement
Normal Cardiac Index (CI) was defined as a value equal to or above 2, while low CI was defined as a value less than 2
Summary
Mixed venous O2 saturation (SvO2) is a clinical marker of global oxygen utilization, and it has been shown to be a surrogate for the interaction between cardiac output, arterial oxygen content and tissue oxygen uptake [1]. The previous studies evaluating the relationship between ScvO2 and SvO2 showed a significant variation in results because of different study designs and clinical setup which included intensive care patients with either sepsis, heart failure, or shock [4,5,6,7]. Studies involving such relationship during and after cardiac surgery [8,9,10,11,12,13,14,15] showed contradicting results, this controversy is generating confusion among clinicians and further work is needed to explore this area
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