Effects of Colloid versus Crystalloid Priming Solutions on Tissue Oxygen Saturation during Cardiopulmonary Bypass: A Prospective Randomized Study

Background and Aims: The optimal composition of cardiopulmonary bypass (CPB) priming solutions remains uncertain. Tissue oxygen saturation (StO₂) provides a non-invasive measure of the balance between local oxygen delivery and utilization. This study compared perioperative changes in StO₂ between crystalloid and colloid CPB priming strategies and evaluated the relationship between StO₂ and global perfusion variables.
Methods: Forty-two adult patients undergoing elective coronary artery bypass graft surgery were prospectively enrolled and randomly allocated in a 1: 1 ratio to receive either 1000 mL of Ringer’s solution (n = 21) or 1000 mL of 6% hydroxyethyl starch (HES 130/0.4; n = 21) as the principal CPB priming fluid. Thenar StO₂ was continuously monitored and recorded at nine predefined perioperative time points. The longitudinal course of StO₂ was evaluated using a two-group, nine-time-point mixed repeated-measures analysis with Greenhouse–Geisser correction. Pairwise within-group comparisons were adjusted using the Holm method. Associations between StO₂ and global perfusion variables were evaluated using Pearson and Spearman correlations.
Results: StO₂ changed significantly over time (p < 0.001). Neither the overall group effect (p = 0.868) nor the group × time interaction (p = 0.407) was significant. In the HES group, post-CPB StO₂ was positively correlated with post-CPB central venous oxygen saturation (ScvO₂) (Pearson r = 0.567, p = 0.007; Spearman ρ = 0.472, p = 0.031). The post-CPB StO₂–ScvO₂ Pearson correlation differed significantly between groups (p = 0.038).
Conclusion: StO₂ changed significantly during the perioperative course, but its temporal pattern did not differ between Ringer’s solution and HES priming. The relationship between post-CPB StO₂ and ScvO₂ differed significantly between groups, with a positive association observed in the HES group. This secondary finding should be considered hypothesis-generating.