The investigators aimed to investigate the effects of pretreatment with different doses of dexmedetomidine on the cough caused by fentanyl during anesthetic induction.

Patients undergoing elective surgeries under general anesthesia will be randomly allocated to 4 groups (n = 60, each group). Dexmedetomidine 0, 0.03, 0.06, and 0.09 μg/kg/min will be pump-administered in 10 mins to groups I, II, III, and IV, respectively, followed by the induction of general anesthesia with intravenous fentanyl 4 μg/kg. The incidences and severity of cough that occurred within 2 min after the injection of fentanyl will be recorded, and the incidences of cardiovascular adverse events that occurred between the administration of the dexmedetomidine infusion and 2 min after tracheal intubation will be recorded.

Inclusion Criteria:

• Patients undergoing elective surgeries under general anesthesia.

Exclusion Criteria:

• Patients with contraindications of dexmedetomidine.
• Patients younger than 18 years old and older than 65 years old.