The relationship between mixed venous oxygen saturation and cardiac output in mechanically ventilated coronary artery bypass graft patients.

This study examined the relationship between mixed venous oxygen saturation (SvO2) and cardiac output (CO) in coronary artery bypass graft (CABG) surgery patients, age 35 to 70 years, who were 6.0 to 9.5 hours postoperative, hemodynamically stable, and receiving mechanical ventilation. A total of five paired measurements of SvO2 and thermodilution CO's were recorded on 30 subjects during a 45 minute time period. Correlations between SvO2 and CO for the entire sample ranged from 0.27 (NS*) to 0.45 (p less than or equal to 0.01). Additional analysis was done to determine if continuous infusions of vasoactive drugs influenced the relationship between the variables. Correlations for those on continuous vasoactive medications ranged from 0.21 to 0.31 (NS). Correlations for subjects who did not require vasoactive infusions were higher, ranging from 0.53 (NS) to 0.81 (p less than or equal to .01). Although many results were statistically significant, correlations less than 0.7 should not be used for clinical decision making. SvO2 reflects the overall tissue oxygenation and should not be used as a substitute for CO measurements in the CABG patient in the early hours after cardiac surgery.