Lumbar epidural analgesia with bupivacaine in labor. Determination of drug concentration and pH in fetal scalp blood, and continuous fetal heart rate monitoring.

Lumbar epiduval analgesia with bupivacaine was given to 37 women for uncomplicated labor. After the blcokade serial determinations of pH and bupivacaine concentration were made in fetal scalp blood and maternal venous blood and there was continuous monitoring of the fetal heart rate. Fetal scalp blood pH was within normal limits and no pathologic FHR tracings were elicited by the blockade, although a temporary decrease of the baseline fetal heart rate irregularity was seen in about one-fifth of the cases. Fetal drug concentrations were low and about one-fourth of corresponding maternal values. After reinjection of bupivacaine the degree of drug accumulation was fairly similar in fetal and maternal blood.