After thyroid surgery, the incidence and severity of coughing is important because it may cause serious complications, such as bleeding in the surgical field, laryngospasm, and cardiovascular disturbance. Several studies have shown that the single-dose of dexmedetomidine is effective for reducing cough and agitation during emergence from general anesthesia.

To test the hypothesis that single-dose of dexmedetomidine combined with a low-dose remifentanil infusion during emergence from general anaesthesia could reduce coughing as good as high-dose remifentanil infusion, we will evaluate the efficacy on cough suppression and reduction of side effect of remifentanil using non-inferiority trial.

Inclusion Criteria:

• Thyroid disease undergoing thyroidectomy
• age 20-65
• Amerian society of anesthesgiologist class 1 or 2

Exclusion Criteria:

• chronic cough
• difficult intubation
• liver disease
• uncontrolled hypertension