Objective To observe the effect of combined dexmedetomidine with ropivacaine on neurotransmitter of ultrasound-guided femoral nerve block. Methods Eighty patients undergoing unilateral total knee arthroplasty under general anesthesia were evenly randomized to dexmedetomidine combined with ropivacaine group(group D)and ropivacaine group(group R).Analgesic pump drug formula for postoperative analgesia in group D was 200mL(1.25g/L)of ropivacaine plus dexmedetomidine4μg/kg and that in group R was 200mL(1.25g/L)...