Venoarterial PCO[2] difference: a marker of postoperative cardiac output in children with congenital heart disease

ABSTRACT

To determine the relationship between venoarterial carbon dioxide gradient [delta pCO[2]] and central venous oxygen saturation [ScvO[2]] in children after cardiac surgery. A cohort study. The Paediatric cardiac intensive care unit of the Aga Khan University Hospital, Karachi, from June 2006 to May 2007. 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 ScvO[2] and delta pCO[2]. 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 pCO[2] was 40.50 +/- 9.06 mmHg. One hundred seventy four samples had ScvO[2] > 70% with mean delta pCO[2] of 5.44 +/- 2.55 mmHg and 98 samples had ScvO2 < 70% with mean delta pCO2 of 9.07 +/- 3.90 mmHg. With ScvO[2] < 70%, 77 samples had delta pCO[2] of > 6 mmHg while only 21 samples had delta pCO2 of < 6 mmHg [p < 0.001]. On the contrary with ScvO[2] > 70%, 71 samples had delta pCO[2] of > 6 mmHg and 103 samples had delta pCO[2] of < 6 mmHg. Coefficient of correlation [R[2]] between 0.340 was ScvO[2] and delta pCO[2]. Elevated delta pCO[2] is practical and can be utilized as a useful adjunct to low ScvO[2] in the assessment of low cardiac output syndrome in children after cardiac surgery