Maintenance of a remifentanil infusion during anesthetic emergence has been reported to decrease the incidence of coughing and thereby help to ensure a smooth emergence. It may, however, cause respiratory depression and possibly delay emergence. The purpose of this study was to investigate the effect of different dose of dexmedetomidine infusion on cough suppression during emergence from general anesthesia in patients undergoing thyroid surgery.

American Society of Anesthesiologists physical status I-II adults undergoing elective thyroidectomy under general anesthesia are recruited and randomly allocated to receive dexmedetomidine iv infusion of 0.2μg·kg-1·h-1 (Group D1, n = 100), 0.5μg·kg-1·h-1 (Group D2, n = 100), 0.7μg·kg-1·h-1 (Group D3, n = 100) or saline (Group C, n = 100). Primary outcome is the incidence of coughing during emergence. Second outcomes include severity of coughing, which is assessed using a four-point scale; Ramsay score, Bruggrmann comfort scale score, VAS pain score are recorded. The respiratory rate (RR), heart rate (HR), and mean arterial pressure are also recorded.

Inclusion Criteria:

1. 30Kg/m2 ≥ BMI > 18Kg/m2;
2. undergoing general anesthesia;
3. ASA physical status I and II
4. undergoing elective thyroid surgery.

Exclusion Criteria:

1. hyperthyroidism;
2. preoperative bradycardia;
3. liver function impairment;
4. renal function impairment;
5. heart function failure;
6. history of asthma or COPD;
7. history of diabetes;
8. cognition function impairment;
9. pregnant or lactating women