Use of venous-to-arterial carbon dioxide tension difference to guide resuscitation therapy in septic shock

Figure 1 CO₂ dissociation curve. CO₂ content (mL/100 mL) vs CO₂ partial tension (PCO₂). Differences between the curves result in higher CO₂ content in the blood, and smaller PCO₂ differences between arterial and venous blood. Hemoglobin-O₂ saturation affects the position of the CO₂ dissociation curve (Haldane effect).

Figure 2 CO₂ dissociation curve. CO₂ content (mL/100 mL) vs CO₂ partial tension (PCO₂). Each curve is described at constant base excess (BE). As displayed, for the same CO₂ content, changing the BE results in a great change in PCO₂.

Figure 3 Relationship between the mixed venous-to-arterial PCO₂ difference P (v-a) CO₂ and cardiac output. For a constant total CO₂ production (VCO₂), changes in cardiac output result in large changes in P (v-a) CO₂ in the low values of cardiac output, whereas changes in cardiac output will not result in significant changes in P (v-a) CO₂ in the high values of cardiac output.

Figure 4 ScvO₂-∆PCO₂ guided protocol. ScvO₂: Central venous oxygen saturation; ∆PCO₂: Central venous-to-arterial carbon dioxide tension difference; SaO₂: Arterial oxygen saturation; C (a-cv) O₂: Central arteriovenous oxygen content difference; DO₂: Oxygen delivery; PEEP: Positive end expiratory pressure; red arrows: Increasing.