Abstract
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.
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