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

Abstract Purpose To explore the relationship between centralvenous-to-arterial carbon dioxide difference (P cva CO 2 ), P cva CO 2 /arterial-venous oxygen content difference ratio (P cva CO 2 /C av O 2 ) and the microcirculatory status, evaluated by using near-infrared spectroscopy, in septic shockpatients. Methods Observational study in a 30-bed mixed ICU. Fifty septic shockpatients 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 (StO 2 ), and local hemoglobin index (THI) were measured on the thenar eminenceby means of near-infrared spectroscopy. A transient vascular occlusiontest was performed in order to obtain StO 2 deoxygenationrate (DeO 2 ), local oxygen consumption (nirVO 2 ), and reoxgenation rate (ReO 2 ). Results At inclusion, increased P cva CO 2 values were associated with lower StO 2 and THI, whereas increased P cva CO 2 /C av O 2 values were associated with lower DeO 2 , nirVO 2 , and ReO 2 . Multiple regression models confirmed the association between P cva CO 2 /C av O 2 and nirVO 2 , while P cva CO 2 was only related to CI, and not to microcirculatory parameters. Conclusions In a population of early septic shockpatients, increases in P cva CO 2 and P cva CO 2 /C av O 2 reflected different alterations at the microcirculatory level. While P cva CO 2 was related to global flow, the P cva CO 2 /C av O 2 ratio was associated to impaired local oxygen utilization and diminished microvascular reactivity.