Nunez S. Maisel A. Comparison between mixed venous oxygen saturation and thermodilution cardiac output in monitoring patients with severe heart failure treated with milrinone and dobutamine. American Heart Journal. 1998;135(3):383-8.
Although thermodilution cardiac output (COtd) is the accepted method for monitoring patients with heart failure in the intensive care unit, it is particularly inaccurate in low-flow states and in the presence of tricuspid regurgitation; in addition, it does not adequately reflect the interaction between oxygen delivery and tissue oxygen extraction. The authors were concerned about the underuse of mixed venous oxygen saturation (SvO2) in this setting and hypothesized that it might be a more useful parameter than COtd for evaluating hemodynamic status and monitoring therapy in patients with severe congestive heart failure. The authors determined the correlation coefficients between increasing dose of inotrope and each of the parameters COtd and SvO2 in 18 patients with congestive heart failure who received a 3-day trial of either milrinone or dobutamine during admission to the Veterans Affairs Medical Center in San Diego. In addition, the authors analyzed reproducibility of repeated COtd and SvO2 measurements taken at a single dose of inotrope. In patients receiving milrinone the increase in dose correlated much better with SvO2 (average correlation coefficient 0.79) than with COtd; this stronger correlation with SvO2 was seen in 82% of the trials reviewed (p < 0.05). In addition, the authors found that repeated SvO2 measurements taken at a single dose of milrinone were more reproducible than COtd as indicated by smaller relative 95% confidence intervals. In patients receiving dobutamine no significant trend in correlation coefficients or reproducibility was observed. The authors conclude that there is a significant relation between SvO2 and increasing dose of milrinone therapy in patients with severe heart failure and tricuspid regurgitation that has practical value for physicians monitoring these patients in the intensive care unit. The authors suggest this study demonstrates the worth of SvO2 in detecting hemodynamic change during trials of milrinone therapy and that this parameter may in fact be more reproducible than traditional thermodilution methods.