Variations in central venous oxygen saturation and central venous-to-arterial carbon dioxide tension difference to define fluid responsiveness: a prospective observational study

Introduction Fluid-induced variations in central venous oxygen saturation ( Δ ScvO 2 ) and central venous-to-arterial carbon dioxide tension difference [ Δ P(cv-a)CO 2 ] have been proposed to define fluid responsiveness. This study aimed to determine whether their diagnostic accuracies are affected by baseline values or oxygen consumption (VO 2 ) responsiveness. Materials and methods This prospective observational study enrolled mechanically ventilated patients with circulatory shock. Hemodynamic variables and blood gas analysis were measured before and after a fluid challenge. Fluid responsiveness and VO 2 responsiveness were defined as a ≥10% increase in cardiac index and VO 2 , respectively. The Spearman's rank correlation coefficient (rho) was computed to evaluate the association between variables. The diagnostic accuracy was assessed using the area under the receiver operating characteristic curve (AUC), with subgroup analyses based on baseline ScvO 2 and P(cv-a)CO 2 values and VO 2 responsiveness. Results Out of 58 patients enrolled, 30 were fluid responders. The fluid-induced changes in cardiac index were significantly correlated with Δ ScvO 2 (rho = 0.36, P = 0.006) and Δ P(cv-a)CO 2 (rho = −0.35, P = 0.006). Δ ScvO 2 and Δ P(cv-a)CO 2 defined fluid responsiveness with AUC values of 0.76 [95% confidence interval (CI): 0.63–0.86, P < 0.001] and 0.72 (95% CI: 0.59–0.83, P < 0.001), respectively. A cutoff value of 5% for Δ ScvO 2 and −2 mmHg for Δ P(cv-a)CO 2 yielded positive predictive values of 88% and 75%, and negative predictive values of 63% and 61%, respectively. The gray zones for Δ ScvO 2 (−3 to 4.6%) and Δ P(cv-a)CO 2 (−2.7 to 1 mmHg) comprised 51.7% and 48.3% of the patients, respectively. In the subgroup analyses, Δ ScvO 2 potentially exhibited better accuracy for assessing fluid responsiveness in VO 2 non-responders (AUC of 0.91, 95% CI: 0.78–0.98; 40 patients) and patients with a baseline ScvO 2 < 70% (AUC of 0.84, 95% CI: 0.67–0.95; 32 patients). Meanwhile, the diagnostic accuracy of Δ P(cv-a)CO 2 was slightly improved in VO 2 non-responders (AUC of 0.78, 95% CI: 0.62–0.90; 40 patients) and patients with a baseline P(cv-a)CO 2 ≥ 6 mmHg (AUC of 0.78, 95% CI: 0.62–0.90; 39 patients). Conclusion Δ ScvO 2 and Δ P(cv-a)CO 2 are potential indicators of fluid responsiveness in mechanically ventilated patients with circulatory shock, especially those with abnormal baseline values or VO 2 unresponsiveness.