Central venous-to-arterial carbon dioxide difference combined with arterial-to-venous oxygen content difference (PcvaCO2/CavO2) reflects microcirculatory oxygenation alterations in early septic shock.

PURPOSE: To explore the relationship between central venous-to-arterial carbon dioxide difference (PcvaCO2), PcvaCO2/arterial-venous oxygen content difference ratio (PcvaCO2/CavO2) and the microcirculatory status, evaluated by using near-infrared spectroscopy, in septic shock patients. METHODS: Observational study in a 30-bed mixed ICU. Fifty septic shock patients within the first 24 h of ICU admission were studied. After restoration of mean arterial pressure, hemodynamic, metabolic and microcirculatory parameters were simultaneously evaluated. Local tissue oxygen saturation (StO2), and local hemoglobin index (THI) were measured on the thenar eminence by means of near-infrared spectroscopy. A transient vascular occlusion test was performed in order to obtain StO2 deoxygenation rate (DeO2), local oxygen consumption (nirVO2), and reoxgenation rate (ReO2). RESULTS: At inclusion, increased PcvaCO2 values were associated with lower StO2 and THI, whereas increased PcvaCO2/CavO2 values were associated with lower DeO2, nirVO2, and ReO2. Multiple regression models confirmed the association between PcvaCO2/CavO2 and nirVO2, while PcvaCO2 was only related to CI, and not to microcirculatory parameters. CONCLUSIONS: In a population of early septic shock patients, increases in PcvaCO2 and PcvaCO2/CavO2 reflected different alterations at the microcirculatory level. While PcvaCO2 was related to global flow, the PcvaCO2/CavO2 ratio was associated to impaired local oxygen utilization and diminished microvascular reactivity.