Effects of adding magnesium to bupivacaine and fentanyl for spinal anesthesia in knee arthroscopy

Abstract

Purpose: The aim of the study was to investigate the effects of adding intrathecal magnesium sulfate 50 mg to low-dose bupivacaine-fentanyl on the spread, duration, regression of spinal block, and postoperative analgesia in patients undergoing knee arthroscopy.

Methods: This study was designed in a prospective, randomized, and double-blinded manner. Sixty American Society of Anesthesiologists (ASA) physical status I or II patients were randomly allocated to receive 50 mg magnesium sulfate (3 ml) or 3 ml of preservative-free 0.9% NaCl following 6 mg bupivacaine 0.5% plus 10 microg fentanyl intrathecally. Date were collected regarding the highest level of dermatomal sensory blockade, the time to reach this level from the time of injection of the spinal anesthetic, Bromage scale of motor blockade at the time of reaching maximum sensory level, time for regression of two segments in the maximum block height, time to L(2) regression, time to ambulation, and postoperative analgesic consumption.

Results: The addition of intrathecal magnesium (50 mg) to spinal anesthesia prolonged the time for regression of two segments in the maximum block height and time to L(2) regression, but did not affect maximum sensory level or the time to reach the highest level of sensory block. Even though the mean times to complete recovery of motor function were similar in the two groups, time to ambulation was significantly longer in the magnesium group than in the saline group. Total analgesic consumption in the first 24 h was not decreased significantly with the addition of magnesium to spinal anesthesia, but the time to first analgesic requirement was prolonged significantly.

Conclusion: Even though the time to first analgesic requirement was prolonged significantly by magnesium, the addition of intrathecal magnesium sulfate to spinal anesthesia is not desirable in patients undergoing knee arthroscopy due to the prolonged time to ambulation and the lack of effect of magnesium on postoperative analgesic consumption.