Laryngoscopy and endotracheal intubation may cause tachycardia and hypertension. Magnesium directly inhibits the release of catecholamine from the adrenal medulla, with has a vasodilating effect. Remifentanil indirectly decreases the release of catecholamine by increasing the depth of anesthetic. The effects of magnesium sulfate and remifentanil at attenuating the sympathetic responses were compared during laryngoscopy and endotracheal intubation.

Eighty ASA class 1 or 2 patients, scheduled for elective surgery under general anesthesia, and requiring endotracheal intubation, were divided into four groups. The patient received either normal saline, 50 mg/kg magnesium sulfate, 1.0 µg/kg remifentanil or 25 mg/kg magnesium sulfate and 0.5 µg/kg remifentanil Groups C, M, R and MR, respectively, according to their assigned group. The specific drugs for each group were administered over a 30 second period prior to the induction of anesthesia with 2 mg/kg propofol and 1.5 mg/kg succinylcholine. The Systolic blood pressure, diastolic blood pressure and heart rate were recorded prior to induction (T1), immediately prior to intubation (T2), immediately after intubation (T3), and 1 and 3 minutes after intubation (T4 and T5, respectively).

The percentage changes in the systolic blood pressure of groups M, R and MR were lower immediately after intubation than that of group C. The systolic blood pressures of groups M and MR increased from those at the baseline, but the systolic blood pressure of group R decreased from that at the baseline immediately after intubation. The heart rate of group M increased from that at the baseline, but the heart rate of group R decreased from that at the baseline immediately prior to intubation.

The blood pressure immediately after endotracheal intubation was increased by the administration of magnesium sulfate, but the induced change was less than that of group C. The blood pressure was decreased by the administration of remifentanil immediately after endotracheal intubation. Magnesium sulfate caused tachycardia, but remifentanil caused bradycardia.