Venoarterial PCO₂ difference: A marker of postoperative cardiac output in children with congenital heart disease

Objective: To determine the relationship between venoarterial carbon dioxide gradient (ΔpCO₂) and central venous oxygen saturation (ScvO₂) in children after cardiac surgery. Study Design: A cohort study. Place and Duration of Study: The Paediatric cardiac intensive care unit of the Aga Khan University Hospital, Karachi, from June 2006 to May 2007. Methodology: All children admitted in the paediatric cardiac intensive care after complete repair of congenital heart defect using cardiopulmonary bypass were included in the study. Simultaneous arterial and central venous blood gas samples were obtained from a catheter placed in the artery (either radial or femoral) and superior vena cava respectively. Linear regression analysis was performed between ScvO₂ and ΔpCO₂. Results: Fifty seven children aged from 5 days to 14 years were included and 272-paired simultaneous arterial and central venous samples were analyzed. Mean venous pCO₂ was 47.82±9.03 mmHg and mean arterial pCO₂ was 40.50±9.06 mmHg. One hundred seventy four samples had ScvO₂ > 70% with mean ΔpCO₂ of 5.44±2.55 mmHg and 98 samples had ScvO₂ < 70% with mean ΔpCO₂ of 9.07±3.90 mmHg. With ScvO₂ < 70%, 77 samples had ΔpCO₂ of > 6 mmHg while only 21 samples had ΔpCO ₂ of < 6 mmHg (p < 0.001). On the contrary with ScvO ₂ > 70%, 71 samples had ΔpCO₂ of > 6 mmHg and 103 samples had ΔpCO₂ of < 6 mmHg. Coefficient of correlation (R₂) between 0.340 was ScvO₂ and ΔpCO₂. Conclusion: Elevated ΔpCO₂ is practical and can be utilized as a useful adjunct to low ScvO₂ in the assessment of low cardiac output syndrome in children after cardiac surgery.