Effect of time and adrenaline on the feto-maternal distribution of bupivacaine.

Following lumbar extradural analgesia with 0.5% bupivacaine, the placental transfer of bupivacaine was examined in 40 women undergoing elective and 40 women undergoing emergency Caesarean section. Within each group, the patients received randomly either plain bupivacaine or bupivacaine with adrenaline 1 in 200,000. Plasma bupivacaine concentrations were measured in blood samples taken simultaneously at delivery from the umbilical vein (UV), umbilical artery (UA) and maternal vein (MV). Bupivacaine concentrations in MV, UV and UA were not significantly affected by the presence of adrenaline, but were positively correlated with first dose to delivery interval (FDD) while MV and UV were inversely correlated with last dose to delivery interval (LDD). Mean ratio of UV:MV concentrations of bupivacaine was 0.346 and for UA:MV it was 0.305. There was no significant correlation between any fetal:maternal ratio and FDD or LDD. UA:UV ratio appeared to increase towards unity 30-40 min after the last dose. The presence of adrenaline was associated with an increase in UA:UV in the elective group (P less than 0.01). In eight patients who received adrenaline there was reverse placental transfer (UA:UV greater than 1). There was no evidence of progressive fetal accumulation of bupivacaine beyond 30-40 min.