The patients were randomly assigned to three groups of 20 patients : group 1 , 0.5 mL saline added to 3 mL ( 15 mg ) hyperbaric bupivacaine ; and groups 2 and 3 , 2 g dexmedetomidine and 4 g dexmedetomidine added to 3 mL ( 15 mg ) hyperbaric bupivacaine , respectively .