The Effect of Magnesium Sulfate on Motor and Sensory Axillary Plexus Blockade

BACKGROUND Magnesium is a physiologic cation that blocks neuromuscular transmission and does not allow the nerve to be stimulated. OBJECTIVES This study investigates the effect of adding magnesium sulfate to lidocaine to extend the duration of sensory and motor blocks of the axillary plexus in orthopedic surgeries of the upper extremities. PATIENTS AND METHODS This controlled randomized double-blind study was performed on patients who were candidates for orthopedic surgery of the upper extremities. A total of 60 patients between 18-60 years with ASA Class 1 or 2 participated in the study. One group received lidocaine (5 mg/kg) with magnesium sulfate 20% (3 mL) as the case group, while the second group received lidocaine (5 mg/kg) with normal saline (3 mL) as a placebo to block the axillary plexus using the trans-arterial technique. The duration of the sensory and motor block of the axillary plexus was monitored and evaluated using the pinprick and modified Bromage scale. RESULTS A total of 60 patients were included in the study with 30 patients having received lidocaine plus magnesium and the other 30 patients having received lidocaine plus normal saline. The mean sensory block duration in the case group was 248.83 ± 18.36 and in control group was 204.67 ± 22.62. The mean motor block duration in the case group was 207.0 ± 16.64 and in control group was 147.33 ± 21.52 (both P < 0.0001). The mean onset of sensory block in case group was 15.5 ± 3.79 and the onset block in control group was 10.33 ± 4.13 (P < 0.0001). The mean onset of motor block in case group was 20.66 ± 4.09 and the onset block in control group was 19.73 ± 26.18 (P < 0.848). CONCLUSIONS The addition of magnesium sulfate to lidocaine increased the duration of motor and sensory axillary block in the upper extremities during surgeries when compared to the use of lidocaine alone.