Placental transfer of local anesthetics.

All the presently used local anesthetic agents in the increasingly popular modalities of obstetric regional anesthesia cross the placenta readily, governed only by two factors that the anesthesiologist has any control over (1) dosage and timing of doses and (2) uterine blood flow as it relates to the development of fetal acidosis. Uptake of a given dose of local agent from the epidural or caudal spaces may be limited with the addition of epinephrine to some extent with some drugs, but this is of little real value in the two safest drugs--bupivacaine and 2-chloroprocaine. At the doses and in the manner presently recommended, fetal intoxication with local anesthetic agent during maternal epidural analgesia should not occur in the absence of either direct intravascular injection, severe maternal hepatic disorder, marked fetal prematurity or postmaturity. The usual precautions in the exercise of regional anesthesia when applied to obstetrics render it very safe, if not the safest form of anesthesia-analgesia available.