Usefulness of venous-to-arterial partial pressure of CO₂ difference to assess oxygen supply to demand adequacy: effects of dobutamine

The central venous O₂ saturation value and lactic acid levels are part of the diagnostic and therapeutic work up of patients in shock. These usual indicators of tissue hypoxia don’t fully describe the adequacy of tissue perfusion. There is ample evidence that supplementing this data with the venous-to-arterial partial pressure of CO₂ (PCO₂) difference (ΔPCO₂) complements the clinician’s tools when treating patients with shock. Based on a modified Fick equation as it applies to CO₂, in patients in a steady state, the ΔPCO₂ reflects the cardiac output (CO). This observation has been shown to be of clinical value in resuscitating patients in shock. Moreover, the ΔPCO₂ can be used to titrate inotropes, and differentiate the hemodynamic from the metabolic effect of dobutamine.