Magnesium sulfate in femoral nerve block, does postoperative analgesia differ? A comparative study

BackgroundN-methyl-D-aspartate (NMDA) receptors play a major role in central nociceptive transmission. Recent studies identified NMDA receptors peripherally. Magnesium (Mg) has antinociceptive effects due to its antagonistic effect of NMDA receptors. The aim of this randomized, double-blinded, placebo-controlled study was to assess the potential analgesic effect of Mg when directly applied on the peripheral nerves, as well as to evaluate the efficacy of Mg to facilitate the local anesthetic effect of Bupivacaine during peripheral nerve block.MethodsSixty patients, ASA physical status I, II & III, undergoing laser photocoagulation were randomly divided into 2 equal groups. Both groups received femoral nerve block using nerve stimulator. Patients of group A were given Bupivacaine and Magnesium sulfate, while patients of group B were given Bupivacaine and saline. Pain was assessed using Visual analogue scale (VAS). The duration of action of Bupivacaine was determined by assessing the duration of sensory block, as well as, assessing the motor block of the quadriceps muscle in both groups. 75 mg of Diclofenac sodium was administered IM as a rescue analgesic. The total dose of the Diclofenac sodium used was recorded.ResultsThe current study showed a significantly shorter duration of action of Bupivacaine, with a significantly lower pain scores among patients of group A. On the other hand, bearable pain period was significantly shorter, and the total consumption of Diclofenac sodium in the 24 h postoperatively was significantly higher in group B.ConclusionThe current study concluded that the admixture of magnesium to bupivacaine provides a profound prolongation of the femoral nerve block, in addition to a significant decrease in postoperative pain scores and total dose of rescue analgesia, with a longer bearable pain periods in the first postoperative day.