OBJECTIVE: To determine the relationship between the mixed venous oxygen saturation (SvO2) and the cardiac index (CI) in individuals during the first 8 hours after coronary artery bypass grafting.

DESIGN: Descriptive with a correlational design.

SETTING: Cardiac intensive care unit at a university medical center in the midwestern United States.

SUBJECTS: Twenty-one subjects (16 men and 5 women) undergoing coronary artery bypass grafting.

OUTCOME MEASURES: SvO2, thermodilution cardiac output and CI measured every 2 hours during the first 8 hours after surgery.

INTERVENTION: Elective coronary artery bypass grafting.

RESULTS: Significant (p < 0.05) but moderate correlations between SvO2 and CI were found only at 6 and 8 hours after surgery (r = 0.66, p = 0.001; r = 0.44, p = 0.47). Secondary analysis determined that in subjects without lung disease, mixed venous oxygen tension (PvO2) had significant correlation with CI at all data collection times (r = 0.54 to 0.72; p = 0.003 to 0.02).

CONCLUSIONS: The results of this study indicate that immediately after coronary artery bypass grafting, SvO2 cannot reliably predict CI. Although statistically significant results were found for the correlation between PvO2 and CI at all data collection times, the correlations were too low to support the use of the PvO2 as a reliable clinical predictor of CI without further study.