Can measurement of mixed venous oxygen saturation replace measurement of cardiac output in patients with advanced heart failure?

BACKGROUND: Nursing care of patients with advanced heart failure with low ejection fraction requires strict management of IV fluids. Measurement of mixed venous oxygen saturation offers advantages over measurement of cardiac output because no administration of fluid is required and data are obtained continuously. OBJECTIVES: To determine the relationship between mixed venous oxygen saturation and cardiac output in patients with advanced heart failure who have low ejection fraction and to determine if use of vasoactive medications alters the relationship between mixed venous oxygen saturation and cardiac output. METHODS: Simultaneously obtained measurements of mixed venous oxygen saturation and cardiac output were compared in 42 patients with advanced heart failure with ejection fractions of 30% or less (mean, 19.5%). RESULTS: Correlation between mixed venous oxygen saturation and cardiac output was r = 0.54 (P < .001). For subjects not receiving vasoactive medications (n = 28), r = 0.52 (P = .004); for those receiving vasoactive medications (n = 14), r = 0.57 (P = .03). CONCLUSIONS: Similar correlations in the groups receiving and not receiving vasoactive medications suggest that even with pharmacological support, changes in mixed venous oxygen saturation may not be reflected by concomitant changes in cardiac output. Measurement of mixed venous oxygen saturation should not replace measurement of cardiac output for clinical decision making in patients with advanced heart failure with low ejection fraction.