Does Epidural Magnesium Sulfate Cause Medulla Spinalis Injury in Rabbits?

INTRODUCTION: Magnesium is an intracellular ion that has analgesic properties through calcium regulation and N-methyl-D-aspartate receptors. However, the safety of neuroaxial magnesium is not proved. The aim of this experimental study is to investigate the possible neurotoxicologic effects of epidural magnesium sulfate (MgSO4) on medulla spinalis in rabbits.
METHODS: After ethic committee’s approval, 18 male Albino New Zealand rabbits were enrolled into the study. Epidural catheter was inserted into the sacral canal under ketamine. The development of motor and sensorial block 5 min after the administration of 1 mL of 1% lidocaine verified the placement of the catheter. Group Control (n=6): 0.20 mL isotonic saline was administered through epidural catheter. Group M150 (n=6): One mL of 150 mg.mL-1 MgSO4 (~ 0.6 mmol elemental magnesium) (pH=6.20) was administered through epidural catheter, then catheter was flushed with 0.20 mL isotonic saline. Group M450 (n=6): One mL of 450 mg.mL-1 MgSO4 (~ 1.8 mmol elemental magnesium) (pH=6.10) was administered through epidural catheter then catheter was flushed with 0.20 mL isotonic saline. Catheter’s placement was localized by laminectomy. Spinal sections were taken between 5 cm rostral and caudal segments from the tip of the catheter. The sections were stained both hematoxylin-eosin and Cresyl violet. The slides were examined using a light microscope.
RESULTS: Nissl body loss, vacuolization, myelin irregularity, gliosis, and fibrosis in gray and white matter samples were assessed. There were no signs of histological tissue damage. There was no statistically significant histopathological difference between groups.
DISCUSSION AND CONCLUSION: This is the first study that investigates spinal cord injury after epidural magnesium administration to our knowledge. These results are important since epidural route is the second most common route for MgSO4. In this study, we report that, even relatively higher doses of epidural MgSO4 did not cause any spinal cord injury. Further studies need to be performed to adapt these findings to clinical practice.