the Netherlands) was used to evaluate the sublingual microcirculation both at T0 and T6. At each assessment, 5 sequences of 20 seconds each were recorded and stored under a random number. An investigator blinded to the sequence order and patient’s clinical course, analyzed the sequences semi-quantitatively. The vessels were separated into large and small using a cut-off value of 20 µm in diameter. We evaluated the relation between the percentage of small vessels perfused and the Pv-aCO2 using linear and non-linear regressions and Spearman Rho test. A p< 0.05 was considered as significant. Results We found significant but very weak relationships between general hemodynamics or oxygen derived parameters with Pv-CO2.Pv-aCO2 was inversely related to the percentage of small vessels perfused both at T0 and T6 (T0: R 2 :0.515, p< 0.001; T6: R 2 :0.453, p< 0.001).