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

Xiaoyang Zhou¹Hanyuan Fang²Chang Xu¹Jianneng Pan¹Hua Wang¹Tao Pan^1*Zhaojun Xu^1*Bixin Chen^1*

• ¹Ningbo No.2 Hospital, Ningbo, China
• ²Ningbo Yinzhou No.2 Hospital, Ningbo, China

Introduction: Fluid-induced variations in central venous oxygen saturation (ΔScvO2) and central venous to arterial carbon dioxide tension difference [ΔP(cv-a)CO2] have been proposed to define fluid responsiveness. This study aimed to determine whether their diagnostic accuracies are affected by baseline values or oxygen consumption (VO2) 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 VO2 responsiveness were defined as a ≥10% increase in cardiac index and VO2, respectively. The diagnostic accuracy was assessed using the area under the receiver operating characteristic curve (AUC), with subgroup analyses based on baseline ScvO2 and P(cv-a)CO2 values and VO2 responsiveness. Results: Out of 58 patients enrolled, 30 were fluid responders. The fluid-induced changes in cardiac index were significantly correlated with ΔScvO2 (rho = 0.36, P = 0.006) and ΔP(cv-a)CO2 (rho = -0.35, P = 0.006). ΔScvO2 and ΔP(cv-a)CO2 defined fluid responsiveness with AUC values of 0.76 [95% confidence interval (CI): 0.63 to 0.86, P < 0.001] and 0.72 (95% CI: 0.59 to 0.83, P < 0.001), respectively. A cutoff value of 5% for ΔScvO2 and -2 mmHg for ΔP(cv-a)CO2 yielded positive predictive values of 88% and 75%, and negative predictive values of 63% and 61%, respectively. The gray zones for ΔScvO2 (-3 to 4.6%) and ΔP(cv-a)CO2 (-2.7 to 1 mmHg) comprised 51.7% and 48.3% of the patients, respectively. In the subgroup analyses, ΔScvO2 potentially exhibited better accuracy for assessing fluid responsiveness in VO2 non-responders (AUC of 0.91, 95% CI: 0.78 to 0.98; 40 patients) and patients with a baseline ScvO2 < 70% (AUC of 0.84, 95% CI: 0.67 to 0.95; 32 patients). Meanwhile, the diagnostic accuracy of ΔP(cv-a)CO2 was slightly improved in VO2 non-responders (AUC of 0.78, 95% CI: 0.62 to 0.90; 40 patients) and patients with a baseline P(cv-a)CO2 ≥ 6 mmHg (AUC of 0.78, 95% CI: 0.62 to 0.90; 39 patients). Conclusion: ΔScvO2 and ΔP(cv-a)CO2 are potential indicators of fluid responsiveness in mechanically ventilated patients with circulatory shock, especially those with abnormal baseline values or VO2 unresponsiveness.