Magnesium had an inhibitory effect on neuromuscular transmission and caused a decrease in muscle fiber membrane excitability. It reduces the amount of acetylcholine that is released at the motor nerve terminal by decreasing the calcium conductance of presynaptic voltage-dependent calcium channels. After pre-treatment with magnesium, an increased speed of onset and a prolongation of the recovery period of neuromuscular blockade have been observed with other non-depolarizing neuromuscular blocking agent (NMBA) such as atracurium, vecuronium and rocuronium. Rocuronium is the currently preferred NMBA used as an alternative to succinylcholine for rapid tracheal intubation. As an alternative to succinylcholine, high doses of NMBA have been tested for rapid sequence intubation. This excessively high dose of rocuronium, however, prolongs the duration of the neuromuscular block and this may not be warranted in every surgical setting.

The reduction of onset time of rocuronium by magnesium pre-treatment can make intubation condition more rapid and much better clinically. It will thus be interesting to compare intubation conditions of a standard intubation dose of rocuronium after magnesium pre-treatment with high dose of rocuronium or standard dose of rocuronium.

Inclusion Criteria:

• patients undergoing operation under general anesthesia
• American Society of Anesthesiologist physical status I or II
• 20-65 year old male or female

Exclusion Criteria:

• hepatic or renal dysfunction
• respiratory or cardiovascular dysfunction
• neurologic disorder
• neuromuscular disease
• pregnancy
• body mass index (BMI) >30 kg/m2 or <16.5 kg/m2
• anticipated difficult airway
• higher magnesium level than normal range in preoperative evaluation
• chronic medication with calcium channel blocker or magnesium
• history of known allergy to magnesium sulphate or any other study drugs