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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.
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.
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.
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%.