Effects of magnesium sulphate on the analgestic efficacy of femoral nerve block with ropivacaine

Abstract

Objective To evaluate the effects of magnesium sulphate on the analgestic efficacy of nerve block analgesia with ropivacaine. Methods Sixty cases who used femoral nerve block analgesia after unilateral total knee arthroplasty under the general anesthesia were selected, and according to digital table they were randomly divided into two groups(n=30 each): magnesium sulfate plus ropivacaine(group M) and ropivacaine(group C). The solution(20mL) of 0.2% ropivacaine and 0.15% magnesium sulphate were administered to group M, and 20mL solution of 0.2% ropivacaine was given to the group C. The pain score was measured by visual analogue scale(VAS). The supplementary usage and cumulative dosage of morphine were recorded and the analgesia relevant complications were observed. Results The results of this study indicated that 4h, 8h, 12h and 24h after the operation, the VAS scores had no statistically significant difference(all P>0.05) at rest, which in group M was significantly decreased compared with group C at 12h(t=2.800, P=0.009) and 24h(t=2.934, P=0.012) after treated with continuous passive motion (CPM) postoperatively.The cumulative dosages of morphine when patients undergo CPM of knee joint in group M were (2.78±0.32)mg, (2.05±0.16)mg, respectively, which were significantly lower than those in the group C [(4.10±0.85)mg, (2.44±0.25)mg](t=7.960, 2.632, all P<0.05). No obvious analgesia relevant complications occurred in both two groups. Conclusion Magnesium sulphate can enhance the efficacy of postoperative femoral nerve block analgesia with ropivacaine, reduce the usage of morphine without increasing the analgesia relevant complications. Key words: Magnesium sulfate; Ropivacaine; Autonomic nerve block; Anesthesia and analgesia