The maternal plasma levels and placental transfer of bupivacaine following epidural analgesia.

The maternal plasma levels of bupivacaine following epidural administration of 0.5 per cent solution with 1/200,000 adrenaline were determined in twelve patients in labour. After 10 ml (50 mg) peak concentrations occurred 15-30 min later and ranged from 0.22 ^ug/ml to 0.60 ,«g/ml. Plasma levels fell gradually with time after the peak until by 3 hours after injection they were all well below 0.2 jUg/ml. Maternal and umbilical plasma levels of bupivacaine were determined at delivery. The ratio of the foetal to maternal levels varied from 0.14 to 0.86. The highest foetal plasma level obtained in the series was 0.25 wg/ml and the highest maternal level was 0.68 /ig/ml. This value was reached after three 10-ml injections of 0.5 per cent bupivacaine with 1/200,000 adrenaline. The 1-min Apgar scores ranged from 7 to 10.