Epidural lidocaine induces dose-dependent neurologic injury in rats

Although epidural lidocaine administered as a bolus has been shown to cause little neurotoxicity, local anesthetics are often administered repetitively or continuously into the epidural space, and in high doses may induce neurologic injury. We investigated whether epidural lidocaine is neurotoxic when a large dose is continuously administered in rats, and whether the functional impairment and histologic damage is dose dependent. In Experiment 1, 13 rats received a 120-min epidural infusion (at 5 mu L/min) of saline or 2% lidocaine. Four days after infusion, rats given 2% lidocaine developed significantly more prolonged tail-flick latencies and showed more apparent morphologic damage than those given saline. In Experiment 2, 41 rats were randomly divided into 5 groups to receive an epidural infusion of saline for 120 min or 5% lidocaine for 15, 30, 60, or 120 min at a rate of 5 mu L/min. Rats given 5% liclocaine for 120 min developed a significant increase in tail-flick latency. Paw pressure thresholds did not change in any group. Nerve injury scores for rats given 5% lidocaine for 30, 60, and 120 min were significantly higher than those for rats given saline. Significant difference in damage in nerve roots was also observed among rats given the anesthetic for different durations of time; nerve injury scores with 120-min infusion were higher than with 15- and 30-min infusions, and injury with 60-min infusion was greater than with 15-min infusion. In conclusion, these results suggest that epidural liclocaine causes dose-dependent neurotoxicity after continuous infusion in rats.