Dexmedetomidine is a highly selective α2 adrenoreceptor agonist approved by the US FDA for short-term postoperative sedation and analgesia.It can also reduce the stress response without respiratory depression.

In this prospective, randomized, double-blind, placebo-controlled study，we gave dexmedetomidine or saline placebo 1h before operations were over and assessed the effects of dexmedetomidine on stress response and postoperative analgesia in patients undergoing thoracotomy during anesthesia recovery period.

Dexmedetomidine can significantly reduce the emergence agitation and postoperative pain in patients who received chest surgery

Inclusion Criteria:

• American Society of Anaesthesiologists Physical Status (ASA-PS) I or II
• undergoing selective thoracotomy
• weight between 45 and 75kg
• operation time 2-4 hours

Exclusion Criteria:

• history of neurologic disease
• history of chronic analgesics intake
• history of allergic reactions to the experimental durgs
• history of renal insufficiency
• history of hepatic dysfunction
• history of coagulation disorders
• women in lactation
• participating in other studies