Anmerkungen zur pH-Metrie im Nabelschnurblut

Abstract

We report on a case of a premature newborn, delivered at 33rd week of gestation, weighting 1650 grammes, which had extremely low actual pH-values (UA: pH = 6,697; UV: pH = 6,803) but surprisingly good Apgar scores (8-10-10). During the following 6 weeks, the newborn did not present any neurological or other abnormalities. Against the background of this case report, all important variables of the fetal acid-base balance in the blood of the umbilical artery and vein are evaluated (Obstetrical data-base of the Department of Obstetrics and Gynaecology of the University of Tübingen, Prof. Dr. H.A. Hirsch). The study population included 2549 vaginal deliveries of singletons, born at term, without any malformations and without premature rupture of the membranes. In 1% of these newborn, the actual pH values in the blood of the umbilical artery were below 7.100 and 16% below 7.200. Computational analysis shows that in these foetuses, 86% of the foetal acidotic load, which must be eliminated by the mother, is due to foetal CO2 production, whereas only 14% is due to metabolic processes. Therefore, the distribution of actual foetal pH-values can be widely influenced by maternal breathing habits during the third stage of labour. We hypothesize that the wide range of pH-value distribution in different obstetrical departments might be due to a different management of the second stage of labour (duration and quality of bearing-down efforts, control of breathing, anaesthesia...). We conclude therefore, that even extremely low actual pH-values in umbilical blood do not necessarily relate to brain damage.