Lidocaine disposition in mother, fetus, and neonate after spinal anesthesia.

Although it is generally believed that concentrations of local anesthetic in maternal plasma do not reach levels that affect the fetus after spinal anesthesia, there are few studies that have measured drug levels in either maternal or neonatal plasma after spinal anesthesia. The purpose of this study was to document the disposition of lidocaine in mother, fetus, and neonate after spinal anesthesia using gas chromatographic/mass spectrometric measurement of lidocaine and two metabolites of lidocaine. Plasma concentration time curves, fetal/maternal ratios, cord artery/cord vein ratios, and neonatal urine levels were determined in ten patients. The results document that lidocaine is present in maternal and neonatal plasma. Mean (+/- SD) maternal plasma levels (0.65 +/- 0.52 micrograms/ml) were significantly lower than those previously reported after epidural anesthesia (2.09 +/- 1.31 micrograms/ml). Fetal/maternal plasma concentration ratios averaged 0.37 +/- 0.2 and mean cord arterial/cord venous ratios 0.5 +/- 6.7. Lidocaine and its metabolites were present in neonatal urine for longer than 36 hr. This study demonstrates that spinal anesthesia with lidocaine results in neonatal exposure to lidocaine.