High veno-arterial carbon dioxide gradient is not predictive of worst outcome after an elective cardiac surgery: a retrospective cohort study

Alteration of tissue perfusion is a main contributor of organ dysfunction. In cardiac surgery, the importance of organ dysfunction is associated with worse outcome. Central venous-arterial difference in CO₂ tension (ΔCO₂) has been proposed as a global marker of the adequacy of tissue perfusion in shock states. We hypothesized that ΔCO₂ could be increased in case of postoperative organ failure or worse outcome. In this monocentric retrospective cohort study, we retrieved, from our database, 220 consecutive patients admitted in intensive care after an elective cardiac surgery. Four time points were formed: ICU admission, and 6, 24 and 48 h after. A ΔCO₂ below 6 mmHg defined the normal range values. The SOFA score, intensive care unit and hospital length of stay, hospital and 6-month mortality rate were recorded. We compared patient with low ΔCO₂ (<6 mmHg) and high ΔCO₂ (≥6 mmHg). We included 55 (25 %) and 165 patients in low and high ΔCO₂ groups, respectively. The SOFA score, the hospital and 6 months mortality rate were higher in patients with low ΔCO₂. Surprisingly, we did not find results previously published in other surgical settings. In cardiac surgery, ΔCO₂ has a low predictive value of outcome.