Central venous-to-arterial carbon dioxide difference combined with arterial-to-venous oxygen content difference is associated with lactate evolution in the hemodynamic resuscitation process in early septic shock

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.