Foetal acid-base balance at Caesarean section.

Sir,—In the Correspondence section of the Journal (1972, 44, 233) Dr Marx mentioned that foetal acid-base values obtained from umbilical artery blood at Caesarean sections did not correlate with the condition of the newborn infant at birth. I should like to provide evidence that acid-base values of umbilical artery blood are not reliable at Caesarean sections under general anaesthesia. We measured foetal pH, base excess (BE) and Pco, from serial scalp capillary blood samples during 26 Caesarean sections under thiopentone/nitrous oxide/ oxygen anaesthesia. The first scalp sample was obtained in all cases immediately before the induction with thiopentone. The last sample was obtained during the last 2 minutes before the delivery of the foetus in 24 cases. The umbilical cord was double clamped as soon as possible in all 26 cases. Induction-delivery (ID-) time ranged from 4i to 14 minutes (mean 9 min 10 sec). The means (±SD) of foetal scalp capillary blood immediately before the induction of anaesthesia were for pH 7.318 (±0.033), for BE -6.70 (±2.41) m.equiv/1. and for Pco, 37.17 (±6.13) mm Hg. Thirteen of the 26 newborn infants were given an Apgar score of 9 or 10 at the age of one minute, 6 a score of 7 or 8, and 7 a score of 6 or less. The means of the foetal acid-base values immediately before the induction of the anaesthesia did not differ significantly between the three groups of newborn infants. A more detailed description of methodology and the patient material has been published previously (Teramo 1968, Teramo et al., 1971). There was no correlation between the pH of the umbilical artery blood and the condition of the newborn infant or the ID-time (fig. I). However, there was a good correlation between the pH change of foetal scalp capillary blood during Caesarean section and the condition of the newborn infant (fig. 2). The pH difference between the scalp capillary blood obtained immediately before the induction and umbilical artery blood did not correlate with the condition of the newborn infant (fig. 3).