Study Objective: Part 1: To measure ropivacaine levels in the mother and infant at delivery after continuous lumbar epidural infusion. Part 2: To compare epidural ropivacaine to epidural bupivacaine for labor analgesia in regard to effectiveness, motor blockade, and maternal and neonatal effects.Design: Part 1: Open-labelled, non-blind study. Part 2: Randomized, double-blind study.Setting: Labor and delivery units of two academic hospitals.Patients: Part 1: 20 ASA physical status I and II parturients in active labor. Part 2: 81 ASA physical status I and II parturients in active labor.Interventions: For Part 1, 8 to 12 ml of 0.25% ropivacaine was administered through a lumbar epidural catheter to achieve a T-10 dermatomal sensory level. An infusion of 0.25% ropivacaine, 8 to 10 ml/hr, maintained this sensory level. Maternal and umbilical cord blood samples obtained at delivery were analyzed for ropivacaine concentration. For Part 2, anesthetic management was similar to that previously described except patients were randomized to receive either 0.25% ropivacaine or 0.25% bupivacaine. Onset, regression, maximal spread of sensory block, and onset and degree of motor blockage were measured. Contraction pain as assessed using a visual analog scale (VAS), maternal blood pressure, and heart rate were determined every 5 minutes until a stable VAS-contraction score was achieved, and every 30 minutes thereafter. Neonatal assessment included Apgar scores and neurologic and adaptive capacity scores (NACS) at 15 minutes, 2 hours, and 24 hours.Measurements and Main Results: For Part 1, the total and free maternal arterial concentrations of ropivacaine at delivery were 0.64 +/- 0.14 mu g/ml and 0.10 +/- .02 mu g/ml, respectively; the umbilical venous total and free concentrations were 0.19 +/- 0.03 mu g/ml and 0.12 +/- 0.07 mu g/ml, respectively (n = 12). The umbilical arterial and venous concentrations did not differ for both the free and total concentrations. For Part 2, there was no difference between ropivacaine and bupivacaine in the variables measured. Umbilical cord gases and Apgar scores were not different between the two groups; NACS were higher at 15 minutes and 2 hours in the ropivacaine group (p < 0.05) than the bupivacaine group.Conclusion: Both ropivacaine and bupivacaine produced excellent analgesia for labor with no major adverse effect on the mother or neonate. (C) 1997 by Elsevier Science Inc.