Many studies have been conducted for the feasibility of using dexmedetomidine as premedication. However, bradycardia and hypotension frequently occurred following the premedication with dexmedetomidine, either via intramuscular or intravenous route. This is particularly true when using a high dose of dexmedetomidine: a intramuscular dose over 2 μg•kg-1 or a intravenous dose over 1 μg•kg-1 can elicit marked decreases in heart rate and mean arterial blood pressure. Subsequent studies using high-dose dexmedetomidine further revealed the potential impact of its detrimental haemodynamic profile on clinical outcomes. Most studies using high-dose dexmedetomidine were predominantly adopted with the dose-finding study performed by Aho and colleague, whom reported that 2.5 μg•kg-1 dose of intramuscular dexmedetomidine was comparably sedative and anxiolytic to 0.08 mg•kg-1 midazolam. However, few investigations have addressed the clinical effects of low-dose dexmedetomidine as premedication. Considering modern anaesthesia has advanced a long way towards eliminating the routine need for a deep preoperative sedation. It has, therefore, become desirable to asses dexmedetomidine as an effective premedication using a moderate sedative dose to minimize its undesired hemodynamic effects. We set a prospective study to compare the sedative, haemodynamic, adjuvant anaesthetic effects and patient's satisfaction of low-dose dexmedetomidine (1μg•kg-1) with midazolam (0.03 mg•kg-1), the most commonly used premedication, used as an intramuscular injective administration in patients undergoing suspension laryngoscopic surgery under general anaesthesia.

Inclusion Criteria:

• Adult patients aged 18-55 years old, American Society of Anaesthesiologists physical status I, scheduled for elective suspension laryngoscopic surgery of benign vocal fold lesions.

Exclusion Criteria:

• Patients with neurological deficits
• Pregnancy
• Imprisonment
• Morbid obesity (body mass index ≥ 30 kg•m-2)
• Preoperative heart rate <45 beats•min-1
• Second or third degree atrioventricular block
• Antihypertensive medication with α-methyldopa, clonidine or other α2-adrenergic agonist