Adding different doses of intrathecal magnesium sulfate for spinal anesthesia in the cesarean section: A prospective double blind randomized trial

BACKGROUND: There is uncertainty as to whether addition of magnesium sulfate to spinal local anesthetics improves quality and duration of block in the caesarean section. In this randomized double blind clinical trial study, we investigated the effect of adding different doses of intrathecal magnesium sulfate to bupivacaine in the caesarean section. MATERIALS AND METHODS: After institutional approval and obtaining informed patient consent, 132 ASA physical status I-II women undergoing elective cesarean section with spinal anesthesia were randomized to four groups: 1 – 2.5 cc Bupivacaine 0.5%+ 0.2 cc normal saline (group C) 2 – 2.5 cc Bupivacaine 0.5%+ 0.1 cc normal saline+ 0.1 cc magnesium sulfate 50% (group M(50)) 3– 2.5 cc Bupivacaine 0.5%+ 0.05 cc normal saline+ 0.15 cc magnesium sulfate 50% (group M(75)) 4– 2.5 cc Bupivacaine 0.5%+ 0.2 cc magnesium sulfate 50% (group M(100)). Patients and staff involved in data collections were unaware of the patient group assignment. We recorded the following: onset and duration of block, time to complete motor block recovery, and analgesic requirement. RESULTS: Magnesium sulfate caused a delay in the onset of both sensory and motor blockade. The duration of sensory and motor block were longer in M(75) and M(100) groups than group C (P < 0.001). Recovery time was shorter in group C (P < 0.001) and analgesic requirement was more in group C than others (P < 0.001). CONCLUSIONS: In patients undergoing the caesarean section under hyperbaric bupivacaine spinal anesthesia, the addition of 50, 75, or 100 mg magnesium sulfate provides safe and effective anesthesia, but 75 mg of this drug was enough to lead a significant delay in the onset of both sensory and motor blockade, and prolonged the duration of sensory and motor blockade, without increasing major side effects.