In providing pain relief to the parturient, regional anesthesia long was considered less depressant to the newborn infant than general anesthesia. This notion came about because local anesthetic is deposited mear the neural target, whereas general anesthetics must use the bloodstream as an intermediate carrier to the cerebral target. Although the local anesthetic eventually is absorbed into the bloodstream too, maternal concentrations of ≤3μg drug per milliliter blood generally were considered innocuous to the infant.
By the mid-1970s, however, several articles1,2 shattered that complacent assumption. Even though the infants' Apgar scores were near-optimal, delicate tests of the immature motor system disclosed substandard performance. Clinically too, babies delivered of mothers receiving peridural anesthesia often seemed to be "floppy but awake." Moreover, the lidocaine (Xylocaine) or mepivacaine (Carbocaine) used for peridural blockade remained in the fetal bloodstream for several hours after birth.3 Furthermore, epinephrine, frequently added as a local vasoconstrictor
de Jong RH. Bupivacaine Preserves Newborns' Muscle Tone. JAMA. 1977;237(1):53-54. doi:10.1001/jama.1977.03270280055025