To investigate the effects of dexmedetomidine on prolonged tourniquet inflation.Thirty-seven patients scheduled for elective orthopedic surgery were randomly assigned to receive intravenous dexmedetomidine (DEX,0.5 mcg/kg; n = 18) or normal saline (CON; n = 19) before tourniquet inflation of the lower limbs under gener alanesthesia in a double-blinded manner.Arterial blood pressure and heart rate,were recorded every 10 min until 60 min after the start of tourniquet inflation and again immediately after deflation.In the DEX group,arterial pressure was not significantly changed,but in the CON group arterial pressure was significantly increased 40,50,and 60 min after the start of tourniquet inflation.Development of more than a 30% increase in arterial pressure during tourniquet inflation was more frequent in the CON group than the DEX group.Preoperative intravenous dexmedetomidine at a dose of 0.5 mcg/kg,could significantly prevent tourniquet-induced systemic arterial pressure increase in patients under general anesthesia.