Background: In congenital heart surgery, low cardiac output syndrome (LCOS) is a major cause of morbidity in the immediate post-operative period. A decrease in cardiac output leads to an increase in tissue oxygen consumption. Several biomarkers such as venous oxygen saturation (SvO₂), arteriovenous oxygen difference (DavO₂), and lactate can assess tissue perfusion in the presence of LCOS. Recently, central venous to arterial CO₂ difference (ΔCO₂) has been proposed as a biomarker of tissue ischemia that could be used as a predictor of death in neonatal patients. This study aimed to analyze the relationship between ΔCO₂ and immediate post-operative outcomes in pediatric patients undergoing congenital heart surgery and its correlation with DavO₂, SvO₂, and lactate.

Methods: We conducted a longitudinal study of patients aged 0-18 years who underwent congenital heart surgery with or without cardiopulmonary bypass at the Instituto Nacional de Pediatría, from March 2019 to March 2021.

Results: Eighty-two patients were included; the median age was 17 months. About 59% had a ΔCO₂ ≥ 6 mmHg. Patients with ΔCO₂ ≥ 6 mmHg had a vasoactive-inotropic score > 5 (p < 0.001), DavO₂ > 5 mL/dL (p = 0.048), and lactate > 2 mmol/L (p = 0.027), as well as a longer hospital stay (p = 0.043). Patients with ΔCO₂ > 6 mmHg and vasoactive-inotropic score ≥ 10 were 12.6 times more likely to die.

Conclusion: ΔCO₂ is a good marker of tissue hypoperfusion and outcome in the post-operative period of congenital heart surgery.