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.