The optimal management of shock states requires a precise evaluation of several parameters, clinical, biological, hemodynamic, and echocardiographic. Among these, parameters that measure O2 and CO2 consumption are of a great interest, especially PCO2 arteriovenous gradient (PCO2 gap) and O2 arteriovenous difference [D(a-v) O2]. The PCO2 gap best correlates with cardiac output while the PCO2gap/D(a-v)O2 ratio would be earlier and more specific than blood lactate assay in assessing tissue hypoperfusion secondary to shock.

The PCO2 gap and the PCO2gap/D (a-v) O2 ratio have been evaluated from gas measurements of venous blood collected from the pulmonary artery and from the superior vena cava area. However, in some patients the placement of a catheter in the superior vena cava is difficult or even impossible due to thrombosis, vascular occlusions and other reasons… In these cases, the inferior vena cava is used for drugs infusion, nutrition and possibly samples. Gasometric samples in lower cellar territory have not yet been validated and may not be correlated with measurements in upper cellar territory. It is therefore useful for current practice to validate samples in lower cellar territory and demonstrate their correlation with measurements made in upper cellar territory.

During an observation period, in patients with catheters in the superior and inferior vena cava for therapeutic indications (renal replacement therapy,...), the investigators systematically took gas measurements at the femoral and jugular sites. the investigators used these data to assess the correlation of PCO2 gap measurements and carbon dioxide-derived indices according to the harvest site : jugular and femoral venous.

Inclusion criteria:

- All consecutive critically ill patients who had an arterial catheter and a venous catheter in the superior and inferior vena cava were included.

Exclusion criteria:

• An age under 18
• Pregnancy
• Legally protected adults

Critically ill patients

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