![]() ![]() įetal acidemia is most commonly a mixed respiratory and metabolic acidosis. It can give accurate information about the fetal metabolic condition, and its measurement is as helpful as cord arterial pH in predicting poor neonatal outcomes. Lactic acid is the final product of anaerobic metabolism that does not cross the placenta. When combined with other abnormal clinical findings, a base deficit of more than 12 meq/L strongly correlates with adverse neonatal outcomes. In a term newborn with uncomplicated delivery, cord arterial base excess varies from -5.6 to -2.7 meq/L and cord venous base excess from -4.5 to -2.4 meq/L. Īpart from measuring pH, pCO2, and pO2, blood gas analyzers also calculate base excess. Therefore a pO2 value greater than 37.5 mmHg is more likely to have occurred due to the presence of air bubbles in the collected sample. With the mother on supplemental O2, the mean cord arterial pO2 was never found to be higher than 37.5 mmHg. Maternal respirations on room air yielded mean cord venous pO2 of 43.5 mmHg and mean cord arterial pO2 of 31.5 mmHg. A cord pH less than 7, when combined with other abnormal clinical findings, strongly correlates with adverse neonatal outcomes. Preterm newborns were found to have a higher pH, and observations noted a gradual reduction with increasing gestational age. Studies showed that in term infants with uncomplicated delivery, the mean cord arterial pH is 7.24 to 7.27, and the mean cord venous pH 7.32 to 7.34. Since fetal CO2 gets carried by the umbilical arteries, the expectation is that arterial cord blood gas will be slightly more acidotic than venous cord blood gas. Thus, it is always essential to obtain both venous and arterial blood samples for analysis. The severity of cord compression has a significant effect on the arteriovenous pH difference. Consequently, there is more carbon dioxide eliminated through the umbilical arteries, which renders the arterial cord blood more acidotic, while the umbilical venous acid-base status remains equilibrated by the normally functioning placenta. To meet their metabolic demands, fetal tissues will respond by increasing their extraction of oxygen. Thus, in umbilical cord compression, venous flow from the placenta to the fetus decreases more than arterial flow. Veins are more compressible than arteries. Consequently, venous cord blood gas analysis mainly reflects placental metabolism, whereas arterial sampling more accurately reflects fetal metabolism. Oxygenated blood is carried from the placenta to the fetus through the umbilical vein, whereas blood rich in carbon dioxide eliminated by the fetus returns to the placental circulation through the umbilical arteries. ![]() However, umbilical artery blood gas analysis gives more accurate information about the fetal metabolic condition and correlates better with neonatal outcomes. The umbilical vein is easier to sample due to its large diameter. ![]()
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