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

The authors retrospectively compared the correlation of pH and pCO₂ from venous and arterial blood gases following cardiothoracic surgery in neonates, infants, and children. The cohort for the study included 14 infants and children undergoing cardiovascular surgery procedures for correction of congenital 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 obtained for blood gas analysis. The mean venous pCO₂ value was 45 ± 9 mmHg, with a mean arterial pCO₂ 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 was a significantly greater discrepancy between the arterial and venous pCO₂ values when the central venous oxygen saturation was less than 70% compared to when the central venous saturation was ≥70% (p < 0.01). Linear regression analysis of venous versus arterial pCO₂ revealed a slope of 0.62, r = 0.76, and r² = 0.58, The mean venous pH value was 7.42 ± 0.07 and the mean arterial pH value was 7.46 ± 0.07. The overall difference between the venous and arterial pH values was 0.04 ± 0.02. Chi-squared analysis showed that with a central venous oxygen saturation of ≥70%, there were a significantly greater number of values with a venous to arterial pH difference of 0.05 or less compared 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 r² = 0.77. Venous blood gas values do not provide a clinically useful estimate of arterial blood gas values following cardiothoracic surgery in children.