Epidural Administration of Magnesium Sulfate in the Rabbit: Can It Induce Motor and Sensory Blockade?

We investigated whether epidural magnesium sulfate administration can produce motor blockade and/or sensory blockade in rabbits. Control animals (group C) received 1.2 ml isotonic saline, group M received 1 ml 15% (150 mg) magnesium sulfate and 0.2 ml isotonic saline (to flush the catheter), while group L received 1 ml 1% lignocaine and 0.2 ml isotonic saline. On the 1st day, somatosensory evoked potentials (SEPs) were recorded; on the 2nd day, motor blockade was evaluated, and the heart rate, mean arterial pressure (MAP), serum PaCO2, and serum magnesium level were measured. Compared with groups C and M, the MAP in group L was significantly reduced at the 2nd-5th, 15th, and 30th min. Significant motor blockade was found only in group L. No significant difference was found in a comparison of the latencies and amplitudes of SEP waves P and N between groups. Comparisons within the groups showed that the P1 wave latency in group C significantly increased at the 15th min, while the latency of wave N1 showed a significant decrease at the 60th min in group M. The latencies of the N1 and P1 waves showed significant increases at the 5th min in group L. Thus, our study showes that epidural administration of 150 mg magnesium sulfate in rabbits produces no motor or sensory blockade