Effect of intravenous infusion of magnesium sulphate on postoperative analgesia in patients undergoing arthroscopic knee surgeries under spinal anaesthesia

Abstract

INTRODUCTIONSpinal anaesthesia is a popular and time-tested regional anaesthetic technique with good safety profile and high success rate but has a limited duration of action. In recent times, the use of intrathecal adjuvants with sub therapeutic doses of local anaesthetic has become popular as they have a synergistic effect, boosts analgesia, extends the period and rises the intensity of block, provides better patient satisfaction with fewer complications.1 Postoperative pain following arthroscopic knee surgeries is usually moderate to severe in nature. For early rehabilitation and functional recovery, adequate postoperative pain management and satisfactory analgesia is important.Magnesium, a physiological calcium antagonist by blocking NMDA receptors in a voltage dependent manner, abolishes hypersensitisation and produces a reduction of NMDA induced currents. Intrathecal magnesium sulphate has shown to prolong analgesic effects of opiods in spinal anaesthesia as a non competitive NMDA antagonist in the first randomized human study.2 During general anaesthesia, Magnesium sulphate infusion reduced the anaesthetic requirement and postoperative pain and analgesic consumption as demonstrated by numerous clinical trials.3 Magnesium ABSTRACT Background: Magnesium sulphate is being used for postoperative pain relief intravenously, intrathecally and epidurally. Currently, it is also gaining popularity as an adjuvant in blocks. The objective of the study was aimed at the postoperative analgesic effects of magnesium sulphate when given as intravenous infusion in patients undergoing arthroscopic knee surgeries under spinal anaesthesia and to compare the postoperative analgesic effects of magnesium sulphate infusion in a study cohort who received magnesium sulphate with the control cohort who were not given magnesium sulphate and underwent arthroscopic knee surgeries under spinal anaesthesia. Methods: After obtaining ethical committee clearance and consent from the patients, 31 patients each were placed in study cohort and control cohort. Spinal anaesthesia was administered in the lateral decubitus position through the L3-4 or L4-5 interspace. Hyperbaric bupivacaine 0.5% solution with fentanyl 20 μg was injected intrathecally. After spinal anaesthesia, patients received magnesium sulphate 50 mg/kg for 15 min and then 15 mg/kg/hr by continuous intravenous infusion until the end of surgery. The other group did not receive magnesium sulphate infusion. Postoperative pain scores and postoperative analgesic consumption were the primary end points. Results:The results of the study reveal the efficacy of perioperative intravenous infusion of magnesium sulphate in prolonging the spinal block as well as reducing the postoperative pain scores without hemodynamic variability or side effects. Conclusions: Post-operative pain and analgesic consumption was reduced with the use of intravenous magnesium following spinal anaesthesia.