Magnesium Sulphate Versus Fentanyl as Adjuncts to Epidural Anaesthesia for Lower Limb Orthopaedic Surgeries: A Comparative Study.

Introduction: Pain relief for lower limb orthopaedic surgeries is achievable with epidural anaesthesia. This study compared the analgesic effects of epidural anaesthesia with magnesium sulphate or fentanyl adjuvant in patients scheduled for elective lower limb orthopaedic surgeries.

Patients and methods: A double-blind randomisation study was carried out on 96 patients categorised into three groups; M, F, and C. All participants received 18 mL of 0.5% bupivacaine plus 1.5 mL of 75 mg magnesium sulphate in Group M or 50 mg of fentanyl in Group F or normal saline in Group C via the lumbar epidural route. Variables including the onset time of sensory and motor blockade, duration of anaesthesia, and time for postoperative Numerical Rating Scale (NRS) score of 3 were summarised using mean, median, standard deviation, and percentages as appropriate. A P value of <0.05 was considered statistically significant.

Results: Mean onset time for the sensory blockade at T8 was 23.7 ± 5.3, 20.5 ± 3.4, and 17.9 ± 5.6 min for groups C, F, and M, respectively (P = 0.001). The onset time for the motor blockade (Bromage score 3) was 29.8 ± 4.0, 26.6 ± 3.5, and 24.5 ± 5.3 min in groups C, F, and M, respectively (P = 0.001). The duration of epidural anaesthesia was 121.6 ± 31.5, 145.9 ± 29.6, and 167.0 ± 27.0 min in groups C, F, and M, respectively (P = 0.001). The time to attain an NRS pain score of 3 was 133.2 ± 27.7, 151.8 ± 32.4, and 172.0 ± 30.9 min in groups C, F, and M, respectively (P = 0.001).

Conclusion: Magnesium sulphate is better as an epidural adjuvant compared to fentanyl in patients undergoing lower limb orthopaedic surgeries.