Veno-arterial CO2 difference has been considered as a marker of low cardiac output. This study aimed to evaluate the correlation between veno-arterial CO2 difference and cardiac index estimated by MostCareTM in children after cardiac surgery and its association with other indirect perfusion parameters and the complex clinical course (vasoactive inotropic score above 15 or length of stay above 5 days).

Data from 40 patients and 127 arterial and venous CO2 measurements for gap calculation taken 0–5 days postoperatively were available. The median (range) veno-arterial CO2 difference value was 9 (1–25 mmHg). The correlation between veno-arterial CO2 difference and cardiac index was not significant (r: −0.16, p = 0.08). However, there was a significant correlation between veno-arterial CO2 difference and vasoactive inotropic score (r: 0.21, p = 0.02), systolic arterial pressure (r: −0.43, p = 0.0001), dP/dtMAX (r: 0.26, p = 0.004), and arterio-venous O2 difference (r: 0.63, p = 0.0001). Systolic arterial pressure (OR 0.95, 95% CI 0.90–0.99), dP/dtMAX (OR 0.00, 95% CI 0.00–0.06), lactates (OR 1.87, 95% CI 1.21–3.31), and veno-arterial CO2 difference (OR 1.13, 95% CI 1.01–1.35) showed a significant univariate association with the complex clinical course. In conclusion, veno-arterial CO2 difference did not correlate with cardiac index estimated by MostCareTM in our cohort of post-cardiosurgical children, but it identified patients with the complex clinical course, especially when combined with other direct and indirect variables of perfusion.