Utility of Venous-to-Arterial Carbon Dioxide Tension Difference in Resuscitation of Septic Shock

Abstract

Acute circulatory failure in septic shock will produce macro- and microcirculatory disorders leading to tissue hypoxia. The venous-to-arterial carbon dioxide tension difference is the difference between partial pressure of CO₂ in mixed venous (gapPCO₂) or in central venous blood (ΔPCO₂) and in the arterial blood. It depends on the cardiac output, the global CO₂ production, and the relationship between PCO₂ and the CO₂ content (CCO₂). Measuring the ΔPCO₂ during the resuscitation of septic shock patients might be beneficial when determining when to continue reanimation despite a central venous oxygen saturation (ScvO₂) > 70% and a high blood lactate level. Because hyperlactatemia is not a discriminatory factor in determining the source of the cellular stress, an increased ΔPCO₂ (> 6 mmHg) could be used to identify patients who remain inadequately resuscitated. Decreasing the ΔPCO₂ is a therapeutic goal to adjust cardiac output to the metabolic demand. Moreover, ΔPCO₂ can help to titrate inotropes to adjust oxygen delivery (DO₂) to CO₂ production, or to choose between hemoglobin correction and fluid/inotrope infusion in patients with too low ScvO₂. ΔPCO₂ combined with oxygen-derived parameter, arteriovenous oxygen content difference (C(a-cv)O₂), through the calculation of the ΔPCO₂/C(a-cv)O₂ ratio can be a useful hemodynamic tool to detect the activation of global anaerobic metabolism.