The Effect of the Magnesium Sulfate in Ultrasound-Guided Quadratus Lumborum Block on Postoperative Analgesia: A Randomized Controlled Trial

INTRODUCTION: Quadratus lumborum block (QLB) has proven to be an effective analgesic technique in various abdominal surgeries. Magnesium sulfate as an adjuvant in different nerve blocks has been reported. The aim of this study was to assess the efficacy of magnesium sulfate as an adjuvant to ropivacaine in an ultrasound-guided QLB for postoperative analgesia in laparoscopic gynecologic surgery. METHODS: Ninety patients belonging to American Society of Anesthesiologists (ASA) physical status I or II, aged between 40 and 60 years, scheduled for laparoscopic gynecologic surgery were enrolled. Patients were divided into three groups and received bilateral quadratus lumborum block: ropivacaine group (group N, 0.375% ropivacaine 40 ml + normal saline 4 ml), magnesium sulfate group (group M, 0.375% ropivacaine 40 ml + 10% magnesium sulfate 4 ml), and control group (group C, normal saline 44 ml). Visual analogue scale (VAS) at rest and during activity at 4, 6, 12, 24, and 48 h postoperatively, consumption of morphine, the time of first analgesic request, frequency of rescue analgesia, satisfaction with postoperative analgesia, and any side effects were recorded. RESULTS: VAS scores in groups M and N were significantly lower than in group C at 4 and 6 h postoperatively (P < 0.001). VAS scores were lower in group M at 12 and 24 h postoperatively compared to groups N and C (P < 0.05). The mean total morphine consumption was significantly lower in group M than in groups N and C (P < 0.001). The mean time to the first patient-controlled analgesia (PCA) bolus was significantly prolonged in group M compared to group C (P < 0.05). The satisfaction with postoperative analgesia of group M was superior to that of groups N and C (P < 0.05). There was no significant difference in side effects among the three groups. CONCLUSION: Magnesium sulfate as an adjuvant to ropivacaine in ultrasound-guided QLB prolongs the duration of analgesia, decreases analgesic requirements, and improves patient satisfaction without significant side effects. TRIAL REGISTRATION: Chinese Clinical Trial Registry, ChiCTR1900027066.