Plasma Levels of 2-Chloroprocaine in Obstetric Patients and Their Neonates after Epidural Anesthesia

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Abstract
The purpose of this study was to determine maternal and fetal plasma levels of 2-chloroprocaine after epidural anesthesia during labor and to examine its metabolism by plasma cholinesterase to 2-chloroaminobenzoic acid (CABA). The study population included 33 normal patients whose infants were delivered vaginally or by repeat cesarean section and their infants. Gas chromatographic techniques were used to determine concentrations of 2-chloroprocaine and CABA in plasma; spectrophotometric techniques were used to determine plasma cholinesterase activity. In maternal plasma 2-chloroprocaine was detectable for at least 5-10 min after each dose; mean levels at delivery were 23 .+-. 80 and 51 .+-. 13 ng/ml for patients having cesarean section and vaginal delivery, respectively. In contrast, CABA was detectable throughout labor. In cord blood plasma, 2-chloroprocaine was detectable in 1/2 of the cord-vein and arterial samples analyzed; the highest mean concentration was 17 ng/ml in samples from vaginally delivered infants. CABA was detectable in 3/4 of the cord blood samples. Plasma cholinesterase activity was low in both mothers and neonates, and decreased after anesthesia in both groups. In maternal plasma, cholinesterase activity was 42% less/ml plasma compared with that for nonpregnant controls, and 80% less after anesthesia compared with that measured prior to anesthesia. In cord blood plasma, cholinesterase activity was 22% less than that found in samples from nonpregnant women and 70% less in infants whose mothers received 2-chloroprocaine than in control infants. The decreased activities of maternal and neonatal cholinesterases at term are adequate to hydrolyze most, but not all, of the plasma 2-chloroprocaine following epidural anesthesia during labor.