Comparison of the analgesic effects of intravenous magnesium sulfate infusion versus intrathecal fentanyl in patients with severe pre-eclampsia undergoing caesarean section

Background : A double-blinded, prospective, randomized, controlled study was designed to determine the analgesic efficacy and tolerability of intravenous magnesium sulfate versus intrathecal fentanyl, in patients with severe pre-eclampsia, scheduled for caesarean section, under spinal anaesthesia. Materials and Methods : One hundred and five patients were randomly allocated to one of the three groups; the control group B received spinal anaesthesia with 10 mg of 0.5% heavy bupivacaine, the test group FB received spinal anaesthesia with 10 mg of 0.5% heavy bupivacaine plus 25 ΅g of preservative-free fentanyl and the test group MB received spinal anaesthesia with 10 mg of 0.5% heavy bupivacaine along with intravenous magnesium sulfate (6 gm iv as a loading dose over 20-30 minutes, followed by infusion of magnesium sulfate 2 gm per hour for 24 hours). Results : The time required for the first postoperative analgesic requirement was significantly more in groups FB and MB, as compared to the control group. (Group FB: 6.85 + 1.7 hours, group MB: 7.05 + 1.95 hours and Group B: 3.75 + 0.75 hours). This difference, however, was not significant between group FB and group MB. The frequency of postoperative analgesic requirement was significantly less in the FB and MB groups, as compared to the control group. (Control group: 3.9 + 0.5, group FB 2.3 + 0.25 and group MB: 2.5 + 0.4). Perioperative sedation was significantly higher in group FB as compared to group B and group MB. Nine patients in group FB had postoperative nausea and vomiting, whereas, none of the patients in the control group or group MB experienced this. This difference too was statistically significant. Conclusion : Intravenous magnesium sulfate and intrathecal fentanyl in the doses mentioned, increased the duration of postoperative analgesia in severely pre-eclamptic patients undergoing caesarean section under spinal anaesthesia; however, patients who received intravenous magnesium sulfate experienced lesser side effects than those who received intrathecal fentanyl