Intrathecal magnesium sulfate as a spinal adjuvant in two different doses, combined with 0.5% heavy bupivacaine for infraumbilical surgeries

The spinal anesthesia has the definitive advantage that profound nerve block can be produced in a large part of the body by the relatively simple injection of a small amount of local anesthetic. BACKGROUND AND AIMS: The use of adjuvant drugs with local anesthetics for spinal is intended to improve the success of regional anesthesia. The present study evaluated magnesium sulfate in two different doses and fentanyl as an adjuvant to bupivacaine for spinal anesthesia. MATERIALS AND METHODS: Following Institutional Ethical Committee approval and written informed consent, a prospective randomized double-blinded study was conducted in 81 cases. Patients included were of either gender belonging to American Society of Anesthesiology (ASA) I or ASA II status undergoing elective infraumbilical surgeries of <3 h. Patients were randomized into four groups and were administered an intrathecal solution of (1) Group NS: 3 cc of 0.5% bupivacaine + 0.5 cc of NS. (2) Group F: 3 cc of 0.5% bupivacaine + 25 mcg fentanyl (0.5 cc). (3) Group M 50: 3 cc of 0.5% bupivacaine + 50 mg magnesium sulfate diluted to 0.5 cc with NS. (4) Group M 100: 3 cc of 0.5% bupivacaine + 100 mg magnesium sulfate diluted to 0.5 cc with NS. The variables assessed were visual analog pain scale, pruritus, intensity of motor block and somnolence before and after intrathecal injection at 5, 10, 15, 30, 45, and 60 min in the 1(st) h, at every 30 min in next hour and then hourly thereafter. RESULTS: The mean duration of analgesia in normal saline group, fentanyl group, M 50 and M 100 groups are 272.8 (standard error [S.E.] of mean 22.9), 360.0 (S.E. of mean 28.8), 252.5 (S.E. of mean 15.0), 276.6 (S.E. of mean 29.5) min, respectively. CONCLUSION: The addition of magnesium sulfate in the two different doses (50, 100 mg) does not affect the quality of block or duration of analgesia. However, M 100 is as effective as fentanyl as far as the duration of analgesia is concerned.