Changes in central venous-to-arterial PCO difference and central venous oxygen saturation as markers to define fluid responsiveness in critically ill patients: a pot-hoc analysis of a multi-center prospective study.

Background: The main aim of the study whether changes in central venous-to-arterial CO difference (ΔP(v-a)CO) and central venous oxygen saturation (ΔScvO) induced by volume expansion (VE) are reliable parameters to define fluid responsiveness (FR) in sedated and mechanically ventilated septic patients. We also sought to determine whether the degree of FR was related to baseline ScvO and P(v-a)CO levels.

Methods: This was a post-hoc analysis of a multicenter prospective study. We included 205 mechanically ventilated patients with acute circulatory failure. Cardiac index (CI), P(v-a)CO, ScvO, and other hemodynamic variables were measured before and after VE. A VE-induced increase in CI > 15% defined fluid responders. Areas under the receiver operating characteristic curves (AUCs) and the gray zones were determined for ΔP(v-a)CO and ΔScvO.

Results: One hundred fifteen patients (56.1%) were classified as fluid responders. The AUCs for ΔP(v-a)CO and ΔScvO to define FR were 0.831 (95% CI 0.772-0.880) (p < 0.001) and 0.801 (95% CI 0.739-0.853) (p < 0.001), respectively. ΔP(v-a)CO ≤ 2.1 mmHg and ΔScvO ≥ 3.4% after VE allowed the categorization between responders and non-responders with positive predictive values of 90% and 86% and negative predictive values of 58% and 64%, respectively. The gray zones for ΔP(v-a)CO (- 2 to 0 mmHg) and ΔScvO (- 1 to 5%) included 22% and 40.5% of patients, respectively. ΔP(v-a)CO and ΔScvO were independently associated with FR in multivariable analysis. No significant relationships were found between pre-infusion ScvO and P(v-a)CO levels and FR.

Conclusion: In mechanically critically ill patients, ΔP(v-a)CO and ΔScvO are reliable parameters to define FR and can be used in the absence of CI measurement. The response to VE was independent of baseline ScvO and P(v-a)CO levels. Clinical trial registration The study was registered in the ClinicalTrials.gov registry: NCT03225378, date: July 20, 2017.