In a prospective randomized clinical trial involving adult patients undergoing elective surgery under general anesthesia, the investigators will enroll 216 patients, and evaluate 3 doses of prophylactic dexmedetomidine as a means to reduce postoperative shivering and quality of emergence from anesthesia versus placebo.

Patients undergoing surgery under general anesthesia may experience several complications during the postoperative period. Shivering has been reported to occur in up to 65% of patients recovering from general anesthesia, and has been shown to cause detrimental effects to the patient. Previous studies have shown that dexmedetomidine 1µg/kg at the end of surgery significantly reduces the incidence of postoperative shivering and improves quality of emergence from anesthesia. However, this beneficial effect of dexmedetomidine is at the expense of prolonged time to extubation and awakening. The aim of this study is to find the optimal dose of dexmedetomidine that would be beneficial without delaying recovery from general anesthesia.

Inclusion Criteria:

• 18-80 year-old
• ASA class I, II, and III
• patients undergoing elective surgery under general anesthesia with an estimated time of 1-3 h

Exclusion Criteria:

• duration of surgery less than 1h or more than 3 h
• allergy to dexmedetomidine
• vasoactive antidepressant or analgesics
• obesity (BMI>30)
• fever
• pregnancy