Maternal and foetal plasma bupivacaine concentrations in labour with segmental epidural analgesia

Maternal and foetal plasma bupivacaine concentrations were assayed following segmental epidural analgesia during the first stage of 14 normal labours. Analgesia was accomplished with 20 mg of 0.5% bupivacaine. 10 mothers received only one dose and four mothers two doses. The maternal and foetal plasma bupivacaine levels remained very low and the foetomaternal ratios were about 1:4 during the labour. At delivery, the foeto-maternal ratio increased, showing that the decline of bupivacaine concentrations is slower in foetal than in maternal plasma.