Respiratory quotient estimations as additional prognostic tools in early septic shock.

Central venous-to-arterial carbon dioxide difference (Pcva CO2 ), and its correction by the arterial-to-venous oxygen content difference (Pcva CO2 /Cav O2 ) have been proposed as additional tools to evaluate tissue hypoxia. Since the relationship between pressure and content of CO2 (CCO2 ) might be affected by several factors, some authors advocate for the use of Ccva CO2 /Cav O2 . The aim of the present study was to explore the factors that might intervene in the difference between Pcva CO2 /Cav O2 and Ccva CO2 /Cav O2 , and to analyze their association with mortality. Observational study in a 30-bed mixed ICU. Fifty-two septic shock patients within the first 24 h of ICU admission were studied. After restoration of mean arterial pressure, hemodynamic and metabolic parameters were evaluated. A total of 110 sets of measurements were performed. Simultaneous Pcva CO2 /Cav O2 and Ccva CO2 /Cav O2 values were correlated, but agreement analysis showed a significant proportional bias. The difference between Pcva CO2 /Cav O2 and Ccva CO2 /Cav O2 was independently associated with pH, Scv O2 , baseline Ccva CO2 /Cav O2 and hemoglobin. A stepwise regression analysis showed that pH was the single best predictor for the magnitude of such difference, with very limited effect of other variables. At inclusion, variables associated with ICU-mortality were lactate, pH, Pcva CO2 /Cav O2 , and the difference between Pcva CO2 /Cav O2 and Ccva CO2 /Cav O2 . Initial Scv O2 , Pcva CO2 , Ccva CO2 /Cav O2 , and cardiac index were not different in survivors and non-survivors. In a population of early septic shock patients, simultaneous values of Pcva CO2 /Cav O2 and Ccva CO2 /Cav O2 were not equivalent, and the main determinant of the magnitude of the difference between these two parameters was pH. The Pcva CO2 /Cav O2 ratio was associated with ICU mortality, whereas Ccva CO2 /Cav O2 was not.