Correlation and Prediction of Arterial Partial Pressure of Carbon Dioxide from Venous Umbilical Blood Gases

Background. Arterial partial pressure of carbon dioxide (pCO < sub > 2 < /sub > ) samples are lower in children and higher in fetuses when compared with venous samples. The correlation and prediction of pCO < sub > 2 < /sub > from umbilical venous (UVBG) to umbilical arterial blood gas (UABG) dyad in neonates are identified. Methods. A prospective study was performed from July 2018 to December 2019. Two dependent tests and a multivariate regression model were used to analyze the comparison and correlation tests. Results. A total of 116 paired UABG and UVBG samples were obtained. The medians (interquartile ranges, IQR) were as follows: gestational age of 34 (29-37) weeks, birth weight of 2122 (1146-2839) g, and postnatal age of 2.3 (1.4-10.8) h. The median (IQR) pCO < sub > 2(UABG) < /sub > and pCO < sub > 2(UVBG) < /sub > measurements were 40.2 (33.5-45.8) and 40.4 (34.7-46.8) mmHg, respectively (rho = 0.75, p < 0.001). The median of the differences (IQR) in pCO < sub > 2(UABG) < /sub > and pCO < sub > 2(UVBG) < /sub > was -0.9 (-4.7 to 2.3) mmHg, (p = 0.06). The equation to predict pCO < sub > 2(UABG) < /sub > was 0.9 × pCO < sub > 2(UVBG) < /sub > + 4, as derived from simple linear regression. The best model for predicting pCO < sub > 2(UABG) < /sub > was 0.9 x pCO < sub > 2(UVBG) < /sub > - 0.7 × venous base excess + 0.6 × 5-min Apgar score + 6.1 × meconium aspiration syndrome - 7.7 × patent ductus arteriosus - 6.5 (adjusted r < sup > 2 < /sup > = 0.74). Conclusions. pCO < sub > 2(UVBG) < /sub > correlates with and can predict pCO < sub > 2(UABG) < /sub > . Therefore, pCO < sub > 2(UVBG) < /sub > can be applied to pCO < sub > 2(UABG) < /sub > in neonates for whom UAC insertion is unsuccessful or to avoid an arterial puncture.