Agreement between CO2 gap determined from peripheral blood and mixed venous blood in septic shock patients

Purpose: : The veno-arterial CO2 difference (Pv-aCO2) is a useful marker capable of identifying a subpopulation of shocked patients who present a cardiac output insufficient for the tissue metabolic demands. Some Authors have highlighted a linear relationship between Pv-aCO2 determined by mixed or central venous blood. This research aims to establish whether there is a linear relationship between Pv-aCO2 determined by peripheral venous blood (Pv-aCO2p) and mixed venous blood and the agreement between the two measures. Methods: : Prospective, single-centre, observational clinical study on septic shocked and invasively ventilated patients during the first 24 hours from admission in ICU. Results: : On 38 determinations, t he Bravais-Pearson r between Pv-aCO2 and Pv-aCO2p was 0.70 (95%CI 0.48 – 0.83; p-value = 1.25 x 10^-6). The Bland-Altman test's mean bias was 4.11 mmHg (95%CI 2.82 – 5.39); the repeatability coefficient was 11.05. The differential and proportional bias were 2.81 (95%CI 0.52 – 5.11) and 1.29 (95%CI 0.86 – 1.72), respectively, through the Taffé method. Conclusion: : Pv-aCO2p could be used in clinical settings wider than the ICU alone, where central venous access is not routine, to establish early the adequacy of the circulation and, more specifically, of cardiac output versus tissue metabolic demands in septic patients.