Comparison between 3 Different Doses of Magnesium Sulphate as A Spinal Adjuvant to Bupivacaine and Fentanyl Combination in Lower Limb Orthopedic Surgery

Abstract
Background: Spinal anesthesia is a simple technique that provides a fast surgical block. It has certain limitations such as limited duration of the blockade and post-operative anal-gesia. Adjuncts to the Local Anaesthetics (LA) used in spinal anaesthesia can exhibit undesirable side-effects like respiratory depression, urinary retention, pruritis, haemodynamic insta-bility and nausea and vomiting, limiting their use. Magnesium when used in therapeutic doses avoids all of these side-effects.
Objective: Comparing 3 different doses of Magnesium Sulfate as a spinal adjuvant to Bupivacaine-Fentanyl combi-nation in spinal anesthesia on the spread, duration, regression of spinal block, and postoperative analgesia in patients under-going lower limb orthopedic surgeries.
Patients and Methods: This study was conducted in Assuit University Hospital in period from 1/8/2016 to 31/7/2017. 120 patients aged between 18-60 years, 30 in each group (ASA I or II) scheduled for lower limb orthopedic surgeries were included in our study. The patients were randomly divided into four equal groups of 30 each: Group I (control group) patients received intrathecal injection hyperbaric bupivacaine (0.5%) 2.5ml with fentanyl (25μg) 0.5ml and normal saline 1ml. Group II patients received intrathecal injection hyperbaric bupivacaine (0.5%) 2.5ml with fentanyl (25μg) 0.5ml, MgSO4 (50mg) 0.5ml and normal saline 0.5ml. Group III patients received intrathecal injection hyperbaric bupivacaine (0.5%) 2.5ml with fentanyl (25μg) 0.5ml, MgSO4 (75mg) 0.75ml and normal saline 0.25ml. Group IV patients received intrathecal injection hyperbaric bupivacaine (0.5%) 2.5ml with fentanyl (25μg) 0.5ml and MgSO4 (100mg) 1ml. Onset and duration of sensory & motor block, time to reach the maximum height of the sensory block and incidence of side effects were recorded. Numerical Rating Scale (NRS) was recorded every 6 hours for the next 24 hours.
Results: As regards onset of motor & sensory block, it was delayed in all groups than in control group. As regards duration of motor & sensory block, it was prolonged in all groups than in control group I. The results of our study showed that addition of Magnesium Sulphate to IT Bupivacaine-Fentanyl provides longer duration of analgesia than Bupi-vacaine-Fentanyl alone. Also total analgesic requirements were more in control group than other groups specially group IV which had the least analgesic requirements. As regards side effects our study showed that there were higher incidence of hypotension, nausea & vomiting in group IV when compared with groups II and III.
Conclusion: Our study shows that the addition of magne-sium sulfate to intrathecally bupivacaine-fentanyl in patients undergoing lower limb orthopedic surgery receiving spinal anesthesia prolongs the duration and quality of analgesia better than bupivacaine-fentanyl only but 75mg 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 side effects like hypotension, nasuea & vomiting.