ScvO₂ and Pcv-aCO₂ as complementary tools for goal-directed therapy during high-risk surgery

Introduction

Central venous oxygen saturation (ScvO₂) has been shown to be a useful therapeutic target in septic shock or high-risk surgery. The central venous-to-arterial carbon dioxide difference (Pcv-aCO₂) has been proposed as a complementary tool for goal-directed therapy (GDT) in septic shock. We tested the hypothesis that both ScvO₂ and Pcv-aCO₂ could be used as complementary tools for GDT during high-risk surgery.

Methods

Seventy adult patients, ASA I to III, undergoing major abdominal surgery, were randomly assigned to 6 ml/kg/hour (R-GDT group, n = 36) or 12 ml/kg/hour (C-GDT group, n = 34) of crystalloids. Additional boluses of HES (130/0.4) were given to maintain respiratory variation in peak aortic flow velocity (ΔPV) below 13%. In both groups, ScvO₂, cardiac output (CO), oxygen delivery (DO₂i), Pcv-aCO₂ and postoperative complications were blindly recorded.

Results

At baseline, there were no differences in hemodynamic variables, ScvO₂ (79 ± 7 vs 80 ± 6, P = 0.37) and Pcv-aCO₂ (6 ± 3 vs 6 ± 2, P = 0.95). The total volume of fluid perfused was larger in the C-GDT group than in the R-GDT group (P < 0.01). The two groups showed no differences in intraoperative blood loss, blood transfusion, mean CO and mean DO₂i values. Overall, postoperative complications were increased in the R-GDT group (P < 0.01), especially postoperative sepsis occurred more often (P = 0.0064).

Minimal ScvO₂ (minScvO₂) was higher in the C-GDT group (72 ± 6 vs 69 ± 6%, P = 0.04). In patients with complications, minScvO₂ was significantly reduced (72 ± 6 vs 67 ± 6%, P = 0.0017). minScvO₂ <70% was independently associated with sepsis (OR 4.2 (95% CI 1.1 to 14.4), P = 0.025). Intraoperative mean Pcv-aCO₂ was higher in the R-GDT group (7 ± 3 vs 5 ± 2 mmHg, P < 0.01). In patients who develop sepsis, Pcv-aCO₂ was higher than in patients who did not (8 ± 2 vs 5 ± 2 mmHg, P < 0.01). In patients with ScvO₂ >70% and who develop sepsis, Pcv-aCO₂ was also significantly higher (P < 0.01). The area under the ROC curve was 0.758 (95% CI 0.71 to 0.81) for discrimination of patients with ScvO₂ >70% who did and did not develop sepsis, with 5 mmHg as the best threshold value.

Conclusions

ScvO₂ reflects important changes in oxygen delivery in relation to oxygen needs during the perioperative period and might help guiding GDT better than ΔPV alone. Pcv-aCO₂ appears a useful tool to identify persistent hypoperfusion when GDT is associated with ScvO₂ >70%.