Effects of position changes on mixed venous oxygen saturation in patients after coronary revascularization

The purpose of this study was to investigate the effects of position changes on mixed venous oxygen saturation (SvO2) and to describe the mechanisms responsible for SvO2 changes reported to occur with position changes. The study was done from 4 to 8 hours after surgery in 34 patients after coronary artery bypass grafting. Subjects were put through a series of six position changes, including head of bed elevations and right and left lateral decubitus with return to supine between each. Each position was maintained for 30 minutes. SvO2, arterial oxygen saturation (SaO2), and oxygen consumption (VO2) were measured before and after each position change. Overall mean subject data demonstrated a decrease in SvO2 with each of the lateral position changes. The SvO2 did not drop below 60% in these mean data, and this drop returned to baseline by 5 minutes. There were no significant changes in the mean data for VO2 or SaO2. No significant correlation was found in the mean data between SvO2 and VO2 or SvO2 and SaO2 measurements. Trends were demonstrated in five specific cases that suggested a correlation between changes in SvO2 and changes in VO2 and SaO2. In conclusion, this study demonstrated that subjects were able to tolerate position changes with no clinically significant changes in SvO2, SaO2, or VO2.