The investigators aimed to explore effects of dexmedetomidine on modulation of perioperative blood glucose and relevant hormone during the general anesthesia with surgery time ≥ 4 hours, and the effects on postoperative complications. 75 participants (American Society of Anesthesiologists grades I or II, of both sexes,aged 40-80 yr,with BMI of 18.5-27 kg/m2) scheduled for elective surgery under general anesthesia with surgery time ≥ 4 hours were enrolled in this study. The participants were divided into four groups: group C (control saline group, no dexmedetomidine use), group D1 (dexmedetomidine loading dose 1 mcg/kg, maintenance dose 0.25 mcg/kg/h), group D2 (dexmedetomidine loading dose 1 mcg/kg, maintenance dose 0.5 mcg/kg/h).10 minutes before anesthesia induction, all participants were administrated with dexmedetomidine 1 μg/kg/min.At the beginning of induction, dexmedetomidine was changed to corresponding maintenance dose in each group. Blood samples were taken at the beginning of dexmedetomidine (T0), the beginning of skin incision (T1), 1 h after skin incision (T2), the end of the surgery (T3) and 1 h after patient transfer to PACU (T4) for the value of blood glucose,lactate and relevant hormones. Also, investigators also record the total amount of propofol and sufentanil at the end of surgery,and the complications within 24 h after the surgery.

Inclusion Criteria:

- patients undergoing operations over 4 h under general anesthesia,ASA physical status I or II, irrespective of showing gender bias, aged between 50-75 years old, and having a body mass index (BMI) between 18.5-28 kg/m2.

Exclusion Criteria:

• the patients with bradycardia, hypoglycemia, heart disease, adrenal tumor,diabetes or showed ≥7.0 mmol/L, or HbA1c level ≥6.5%.