Effect of Intravenous Magnesium Sulfate on the Minimum Alveolar Concentrations of Desflurane Using Bispectral Index Monitoring: A Prospective Randomized Double-blind Controlled Study

BACKGROUND: Magnesium sulfate has been implicated to influence the minimum alveolar concentration (MAC) of various volatile anesthetics, but its effect on desflurane remains unanswered so far. AIM: To study the effect of perioperative intravenous magnesium sulfate on MAC of desflurane using bispectral index (BIS) monitoring. SETTINGS: Operating room of a tertiary care hospital. DESIGN: A prospective, randomized, controlled, double-blind clinical trial. METHODS: Sixty American Society of Anesthesiologists Physical Status I/II patients aged 18-65 years and scheduled for breast conservative surgeries were randomized into three groups of 20 each. Control group (Group 1) was administered 100 ml normal saline (NS) as bolus followed by NS infusion. Magnesium (Mg) was administered as bolus of 40 mg/kg in 100 ml NS followed by NS infusion in Group 2 and as bolus of 40 mg/kg followed by infusion of 10 mg/kg/h of Mg in NS in Group 3. Anesthesia was induced with propofol, fentanyl, and atracurium. Dial setting of desflurane was adjusted to target a BIS of 45-55. Time from cessation of desflurane to beginning of spontaneous movement, time taken to respond to verbal commands, time of extubation, and time taken to reach BIS value of 70 were recorded. STATISTICAL ANALYSIS: Statistics was done using SPSS program using ANOVA and the Chi-square test for variables and a P < 0.05 was taken to indicate a significant difference. RESULTS: No significant difference was present in MAC, end-tidal desflurane, and cumulative consumption of morphine. Recovery was similar in Group 2 and Group 3, but time to eye opening (P = 0.011), time to respond to verbal commands (P < 0.001), and time to extubate (P < 0.001) were significantly delayed when compared with patients in Group 1. Hemodynamic changes were comparable among three groups. CONCLUSIONS: From this study, we conclude that MACs of desflurane using BIS as a guide remains unaffected by perioperative infusion of magnesium sulfate.