Lidocaine hydrocarbonate and lidocaine hydrochloride for cesarean section: transplacental passage and neonatal effects

Abstract

Twenty‐six patients, ASA physical status 1, scheduled for elective cesarean section, were divided at random into two groups and received via an epidural catheter 20 ml of 2.2% lidocaine hydrocarbonate (17.3 mg · ml ‐1 lidocaine base) with 5 μg · ml ‐1 epinephrine freshly added (Group CO 2 = 13 patients) or 20 ml of 2% lidocaine hydrochloride (17.3 mg · ml ‐1 lidocaine base) also with 5 μg · ml ‐1 epinephrine freshly added. Following clampage of the umbilical cord (at 40.1 ± 4.9 min after the injection of lidocaine for the CO 2 group and at 41.0 ± 5.4 min for the HCl group), serum concentrations of lidocaine were measured both in the mother and in the umbilical vein. All newborns were examined by the same blinded pediatrician with Apgar scores at 1, 5 and 10 min and with Neurobehavioral Adaptive Capacity Scores (NACS) at 15 min, 2 h and 24 h. The concentrations of lidocaine in the serum were comparable in both groups: in the mothers 8.61 ± 1.48 μmol · l ‐1 for the CO 2 group vs 8.04 ± 2.36 μmol · l ‐1 for the HCl group and in the newborns 3.86 ± 0.84 μmol · l ‐1 for the CO 2 group vs 3.92 ± 0.95 μmol · l ‐1 for the HCl group. The ratio of umbilical vein to maternal vein concentrations of lidocaine was also similar in both groups: 0.45 ± 0.07 for the CO 2 group vs 0.54 ± 0.24 for the HCl group. The percentage of newborns with a normal NACS (score ± 35/40) was equal in both groups, i.e. 91% at 15 min and 2 h of life and 100% at 24 h of life. We conclude that both lidocaine solutions are similar with respect to their transplacental passage and their effects on the neonatal neurobehavioral performance, and that both are safe when used for cesarean section in normal term pregnancy since the majority of newborns (91%) had a normal NACS (score ± 35/40), even at the first evaluation at 15 min of life.