Central Venous-to-Arterial Carbon Dioxide Partial Pressure Difference
Assessing the adequacy of oxygen delivery and oxygen requirements is one of the key steps of haemodynamic resuscitation. For this purpose, clinical examination, lactate and central or mixed venous oxygen saturation (SvO2 and ScvO2, respectively) all have their limitations. Many of these limitations may be overcome by use of the carbon dioxide (CO2)-derived variables. The veno-arterial difference in CO2 tension (“ΔPCO2” or “PCO2 gap”) is not a straightforward indicator of anaerobic metabolism since it is influenced by the oxygen consumption. By contrast, it reliably indicates whether cardiac output is sufficient to carry the CO2 to the lungs in view of its clearance: it reflects the adequacy of cardiac output with the metabolic condition. The ratio of the PCO2 gap with the arteriovenous difference of oxygen content (PCO2 gap/C(A − V)O2) is a reliable marker of the adequacy between oxygen supply and requirements. Conversely to SvO2 and ScvO2, it remains interpretable if the oxygen extraction is impaired in septic shock patients. Compared to lactate, it has the main advantage to change without delay and to provide a real-time monitoring of tissue metabolism.
KeywordsTissue oxygenation Cardiac output Central venous oxygenation Oxygen delivery
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