continuation of remifentanil target controlled infusion (TCI) at effect-site concentration of 2 ng/ml during anesthetic recovery until extubation.

remifentanil TCI discontinuation and dexmedetomidine 0.5 mg/kg intravenous injection before 10 min of the end of surgery

Fifteen minutes before the end of surgery, the first practitioner replace the syringe of remifentanil as new one; new syringe contains remifentanil in remifentanil group (Group R), and normal saline in dexmedetomidine group (Group D), respectively. There are no drug labeling in the new syringe, so the second practitioner can't know which drug was contained in the new syringe. Simultaneously, the second practitioner remifentanil concentration on monitor of TCI pump will be adjusted to 2.0 ng•ml-1. Ten minutes before the end of surgery, 10 ml of dexmedetomidine 0.5 mcg•kg-1 mixed with normal saline will be given for 5 min in Group D; in Group R, 10 ml of normal saline will be given by the first practitioner.

Emergence cough was defined as the cough occurrence during peri-extubation period, from sevoflurane discontinuation to 5 min after extubation. The severity of cough was assessed and recorded by the following cough grading system: Grade 0, no cough; Grade 1, single cough with mild severity; Grade 2, cough persistence less than 5 s with moderate severity; Grade 3, severe, persistent cough for more than 5 s (bucking).