Introduction: Since normal or high central venous oxygen saturation (ScvO₂) values cannot discriminate if tissue perfusion is adequate, integrating other markers of tissue hypoxia, such as central venous-to-arterial carbon dioxide difference (PcvaCO₂ gap) has been proposed. In the present study, we aimed to evaluate the ability of the PcvaCO₂ gap and the PcvaCO₂/arterial-venous oxygen content difference ratio (PcvaCO₂/CavO₂) to predict lactate evolution in septic shock.
Methods: Observational study. Septic shock patients within the first 24 hours of ICU admission. After restoration of mean arterial pressure, and central venous oxygen saturation, the PcvaCO₂ gap and the PcvaCO₂/CavO₂ ratio were calculated. Consecutive arterial and central venous blood samples were obtained for each patient within 24 hours. Lactate improvement was defined as the decrease ≥ 10% of the previous lactate value.
Results: Thirty-five septic shock patients were studied. At inclusion, the PcvaCO₂ gap was 5.6 ± 2.1 mmHg, and the PcvaCO₂/CavO₂ ratio was 1.6 ± 0.7 mmHg · dL/mL O₂. Those patients whose lactate values did not decrease had higher PcvaCO₂/CavO₂ ratio values at inclusion (1.8 ± 0.8vs. 1.4 ± 0.5, p 0.02). During the follow-up, 97 paired blood samples were obtained. No-improvement in lactate values was associated to higher PcvaCO₂/CavO₂ ratio values in the previous control. The ROC analysis showed an AUC 0.82 (p < 0.001), and a PcvaCO₂/CavO₂ ratio cut-off value of 1.4 mmHg · dL/mL O₂ showed sensitivity 0.80 and specificity 0.75 for lactate improvement prediction. The odds ratio of an adequate lactate clearance was 0.10 (p < 0.001) in those patients with an elevated PcvaCO₂/CavO₂ ratio (≥1.4).
Conclusion: In a population of septic shock patients with normalized MAP and ScvO₂, the presence of elevated PcvaCO₂/CavO₂ ratio significantly reduced the odds of adequate lactate clearance during the following hours.