Hydrogen Concentration, Carbon Dioxide Tension and Acid Base Balance in Blood of Human Umbilical Cord and Intervillous Space of Placenta

Abstract

The cord blood of 222 infants has been analysed for pH, PCO2, pO2 and metabolic acid base balance expressed as standard bicarbonate, BB (buffering protein plus buffering bicarbonate) and BE (normal BB minus actual BB). From the placenta 26 samples of intervillous blood have been analysed in the same way and the results are compared with the cord blood in order to show the gas exchange of the foetus. The mean pH after normal delivery is 7.26 in the umbilical artery and 7.33 in the umbilical vein. The mean pCO2 after normal delivery is 45 mm. Hg in the umbilical artery and 38 mm. Hg in the vein. The mean BB after normal delivery is 35 mEq/litre in the umbilical artery and 39 mEq/litre in the vein, indicating that during the passage through the placenta the fetal blood gives up fixed acids to the maternal circulation. In the intervillous blood of the placenta the mean pH is 7.41, themean pCO2 38 mm. Hg and the mean BB 46 mEq/litre. The pCO2 in the umbilical vein and the intervillous space of the placenta are the same, 38 mm. Hg, indicating an almost complete exchange of carbon dioxide between the fetal and maternal circulation.