Background
Magnesium, a physiological antagonist of calcium and N-methyl-D-aspartate receptors (NMDA), has a role in the prevention of pain in patients undergoing surgeries.
Patients and Methods
A prospective randomized double-blinded controlled study was conducted on 60 patients undergoing lower extremities arthroscopic surgery. Spinal anesthesia was given an epidural catheter inserted prior to surgery for postoperative pain management. Postoperatively, patients were randomly allocated into three equal groups. Group I (S group; n 20 patients) patients received epidural saline at a rate of 1ml/h for 24 hours. Group II (MI; n 20 patients) patients received 50mg magnesium sulfate followed by continuous epidural infusion of 100mg at a rate of 4mg/h. Group III (M II; n 20 patients) patients received 50mg magnesium sulfate followed by 500mg at a rate of 20 mg/h. All patients will be provided an infusion of fentanyl 3 mic/ml at a rate of 10 ml/h) via an epidural catheter. The visual analog score, vital signs, time of the first request for rescue analgesia, motor block, need for supplemental analgesic and adverse effects were recorded in the postoperative period.

Results
VAS scores were significantly lower in both MI and MII groups as compared with the control group at the 1st hour and the 2nd hour of the postoperative course.
Conclusion
The addition of epidural magnesium sulfate for postoperative analgesia provided a pronounced significant reduction in postoperative rescue analgesia with no significant difference between the two magnesium doses and minimal side effects.
Keywords:

Lower extremities, orthopedic surgeries, magnesium sulfate, and epidural.