Changes in fetal TCPO2 values occurring during labour in association with lumbar extradural analgesia.

Forty-six of 64 high risk labours were managed with continuous lumbar extradural analgesia. Fetal heart rate (FHR) and continuous transcutaneous PO2 (tcPO2) measurements were made in the 64 patients. Abnormal fetal heart rate patterns and low tcPO2 values associated with the onset of the extradural block were noted in 9% of these cases. A decrease in maternal arterial pressure and uterine hypertonus appeared to be responsible, singly or in combination, for the changes. These effects and the changes in FHR were not seen in the 18 mothers not receiving extradural analgesia. The supine position was associated with slightly smaller fetal tcPO2 values than the preferred lateral positions, with a significant worsening of the fetal tcPO2 values after induction of the extradural block although, overall, extradural analgesia neither improved nor impaired the fetal tcPO2.