Correlation of venous and arterial blood gas values following cardiothoracic surgery in infants and children

The authors retrospectively compared the correlation of pH and pCO(2) from venous and arterial blood gases following cardiothoracic surgery in neonate s, infants, and children. The cohort for the study included 14 Wants and ch ildren undergoing cardiovascular surgery procedures for correction of conge nital heart disease. The patients ranged in age from neonates to 48 months (6.2 +/- 12.3 months) and in weight from 2.9 to 16.1 kg (5.0 +/- 3.2 kg). A total of 95 simultaneous samples of arterial and venous blood were obtaine d for blood gas analysis. The mean venous pCO(2) value was 45 +/- 9 mmHg, w ith a mean arterial pCO(2) value of 37 +/- 7.4 mmHg. The overall difference between the venous and arterial CO2 values was 8 +/- 4 mmHg. The venous to arterial CO2 gradient was greater than 5 mmHg in 78 of 95 samples. There w as a significantly greater discrepancy between the arterial and venous pCO( 2) values when the central venous oxygen saturation was less than 70% compa red to when the central venous, saturation was greater than or equal to 70% (p < 0.01). Linear regression analysis of venous versus arterial pCO(2) re vealed a slope of 0.62, r = 0.76, and r(2) = 0.58. The mean venous pH value was 7.42 +/- 0.07 and the mean arterial pH value was 7.46 +/- 0.07. The ov erall difference between the venous, and arterial pH values was 0.04 +/- 0. 02. Chi-squared analysis showed that with a central venous oxygen saturatio n of greater than or equal to 70%, there were a significantly greater numbe r of values with a venous to arterial pH difference of 0.05 or less compare d to samples with a central venous oxygen saturation of less than 70% (p = 0.002). Linear regression analysis of venous versus arterial pH revealed a slope of 0.84, r = 0.88, and r(2) = 0.77. Venous blood gas values do not pr ovide a clinically useful estimate of arterial blood gas values following c ardiothoracic surgery in children.