Interpretation of venous-to-arterial carbon dioxide difference in the resuscitation of septic shock patients

The venous-to-arterial carbon dioxide difference [P(v-a)CO 2 ] was calculated from the difference of venous CO 2 and arterial CO 2 , which has been used to reflect the global flow in the circulatory shock. Moreover, recent clinical studies found the P(v-a)CO 2 was related to the sublingual microcirculation perfusion in the sepsis. However, it is still controversial that whether P(v-a)CO 2 could be used to assess the microcirculatory flow in septic patients. Moreover, the related influent factors should be taken into account when interpreting P(v-a)CO 2 in clinical practice. This paper reviews the relevant experimental and clinical scenarios of P(v-a)CO 2 with the aim to help intensivists to use this parameter in the resuscitation of septic shock patients. Furthermore, we propose a conceptual framework to manage a high P(v-a)CO 2 value in the resuscitation of septic shock. The triggers of correcting an elevated P(v-a)CO 2 should take into consideration the other tissue perfusion parameters. Additionally, more evidence is required to validate that a decreasing in P(v-a)CO 2 by increasing cardiac output would result in improvement of microcirculation. Further investigations are necessary to clarify the relationship between P(v-a)CO 2 and microcirculation.