Minimal effective dose of magnesium sulfate for attenuation of intubation response in hypertensive patients

Study Objective: To study the minimal effective dose of magnesium sulfate to control blood pressure (BP) during intubation in hypertensive patients. Design: Prospective, randomized, double-blind study. Setting: Operating room of an academic medical center. Patients: 80 adult, ASA physical status 1 and 2, controlled hypertensive patients undergoing elective surgery under general anesthesia and requiring endotracheal intubation. Interventions: Patients were randomized to 4 groups. Patients in study groups received a magnesium sulfate infusion at a dose of 30 (Group I), 40 (Group II), or 50 mg/kg (Group III) before induction of anesthesia, while patients in control group (Group IV) received a 1.5 mg/kg lidocaine bolus 90 seconds before intubation. Anesthesia was induced and maintained with a propofol infusion. Laryngoscopy and intubation were performed 4 minutes after administration of vecuronium. Measurements: Heart rate (HR) and BP were recorded before, during, and after endotracheal intubation for10 minutes. Measures to manage hemodynamic instability were recorded. Serum magnesium levels were also recorded. Main Results: The changes in HR were comparable among groups. Mean arterial pressure (MAP) was maintained within normal limits in Group I patients while Groups II and III patients showed a significant decrease in MAP (P = 0.01) compared with baseline. A total of 6 patients (30%) in Group II and 10 patients (50%) in Group III required interventions (P = 0.001). No patient in Group I and only one patient (5%) in Group IV required intervention. Conclusions: Magnesium 30 mg/kg is the optimum dose to control BP during intubation in hypertensive patients. A further increase in the dose of magnesium may cause significant hypotension. (C) 2013 Elsevier Inc. All rights reserved.