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

Central venous-to-arterial carbon dioxide difference (PCO), and its correction by the arterial-to-venous oxygen content difference (PCO/CO) have been proposed as additional tools to evaluate tissue hypoxia. Since the relationship between pressure and content of CO (CCO) might be affected by several factors, some authors advocate for the use of CCO/CO. The aim of the present study was to explore the factors that might intervene in the difference between PCO/CO and CCO/CO, 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 PCO/CO and CCO/CO values were correlated, but agreement analysis showed a significant proportional bias. The difference between PCO/CO and CCO/CO was independently associated with pH, SO, baseline CCO/CO 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, PCO/CO, and the difference between PCO/CO and CCO/CO. Initial SO, PCO, CCO/CO, and cardiac index were not different in survivors and non-survivors. In a population of early septic shock patients, simultaneous values of PCO/CO and CCO/CO were not equivalent, and the main determinant of the magnitude of the difference between these two parameters was pH. The PCO/CO ratio was associated with ICU mortality, whereas CCO/CO was not.