Effects of adjunct intrathecal magnesium sulfate to bupivacaine for spinal anesthesia: a randomized, double-blind trial in patients undergoing lower extremity surgery.

ABSTRACT

PURPOSE: The aim of this study was to evaluate the effect of additional magnesium sulfate (MgSO(4)) 100 mg to intrathecal (IT) isobaric 0.5% bupivacaine 3 ml on spinal anesthesia in patients undergoing lower extremity orthopedic surgery. METHODS: In a double-blind randomized clinical trial, 79 American Association of Anesthesiologists (ASA) I or II adult patients undergoing lower extremity orthopedic surgery were recruited. The patients were randomly allocated to receive 100 mg MgSO(4) 5% (0.2 ml) plus 15 mg of bupivacaine 0.5% (MgSO(4) group) or 15 mg bupivacaine 0.5% combined with 0.2 ml normal saline (control group) intrathecally. Response to treatment was assessed as onset and duration of sensory block, the highest level of sensory block, time to complete motor block recovery, duration of spinal anesthesia, and postoperative analgesic requirement. RESULTS: The onset of the sensory block was slower in the MgSO(4) group than in the control group (13.3 vs. 11.6 min, P = 0.04), and the duration of the sensory blockade was significantly longer in the MgSO(4) group than the control group (106.5 vs. 85.5 min, P = 0.001). Total analgesic requirements for 24 h following surgery were lower in the MgSO(4) group than in the control group (96.8 vs. 138.5 mg, P = 0.001). Mean duration of spinal anesthesia was not significantly different between two groups (178.0 vs. 167.4 min, P = 0.23). CONCLUSION: In patients undergoing lower extremity surgery with spinal anesthesia, the addition of 100 mg IT MgSO(4) to 15 mg bupivacaine without opioid supplement, prolonged the duration of the sensory block, decreased postoperative analgesic consumption, and significantly prolonged the onset of spinal anesthesia.