OBJECTIVE:To study the relationship between the sensory-motor separation effect of ropivacaine brachial plexus block and the drug concentration of ropivacaine hydrochloride injection under the guidance of ultrasound and nerve stimulator

and explore the feasibility of prolonging the effect of sensory-motor separation.METHODS:Two hundred and eighty patients with normal upper limb nerve

muscle and joint function treated with hand surgery were divided into 10 groups（5 groups each of R1-R5 and RD1-RD5） via random number table

with28 cases in each group.All patients were treated with ultrasound and nerve stimulator to guide clavicle superior clavicle block.Patients in the R1-R5 group received 40 ml of ropivacaine hydrochloride injection with concentrations of 0.20

0.25

0.30

0.35 and 0.40 mg/ml

respectively.Patients in the RD1-RD5 group were given ropivacaine hydrochloride injection（with corresponding dose to the R1-R5 group） combined with dexamethasone 5 mg.The effect of drugs on the block of motion and sensation was evaluated among 10 groups

and the appropriate dose of sensorymotor separation was screened.RESULTS:There was no significant difference in surgery time among 10 groups（P >0.05）.The degree of motor and sensory block in 10 groups of patients deepened with increasing concentration

the onset time decreased

and the maintenance time was prolonged

with statistically significant differences（P < 0.05）.The onset time of the RD1-RD5 group was the same as that of the same dose R1-R5 group

with no statistically significant difference（P>0.05）

and the maintenance time was prolonged

the difference was statistically significant（P<0.05）.Different dose groups had different degrees of motor nerve block at same time points

with statistically significant differences（P < 0.05）.Compared with other groups

the incidence of intraoperative pain and additional anesthetics in the R1

RD1

R2 and RD2 group was statistically significant（P<0.05）.Patients in the R3 and RD3 group had good analgesia effect and maintained good muscle tension.CONCLUSIONS:The use of 40 ml ropivacaine hydrochloride injection（0.30 mg/ml） for the sensory motor separation of the ropivacaine brachial plexus block is effective.The addition of 5 mg of dexamethasone injection can not affect the onset of action or the degree of block

yet significantly prolong the duration of action of the anesthetic drug.