Effect Of Ropivacaine Combined With Dexmedetomidine On Compound Action Potential Of Rabbit Sciatic Nerve Trunk

Objective: To establish animal model of sciatic nerve block on New Zealand rabbit,and observe the latency and nerve conduction velocity of compound action potential of sciatic nerve trunk blocked by ropivacaine combined with dexmedetomidine,explore the possible mechanism of dexmedetomidine as adjuvant of local anesthetics enhancing the effect of peripheral nerve block.Methods: 20 New Zealand Rabbits were randomly divided into 4 groups which were ropivacaine group(R group,n=5),dexmedetomidine group(D group,n=5),ropivacaine combined with dexmedetomidine group(RD group,n=5),and normal saline group(N group,n=5).General anesthesia was administrated on all of the rabbits whose bilateral sciatic nerves were exposed,then the animal models were accomplished.The rabitts of R group were administrated 0.375% ropivacaine 2.5ml beside the left sciatic nerve.The rabitts of D group were administrated 1.5μg/kg dexmedetomidine 2.5ml beside the left sciatic nerve.The rabitts of RD group were administrated 0.375% ropivacaine containing 1.5μg/kg dexmedetomidine 2.5ml beside the left sciatic nerve.The rabitts of N group were administrated normal saline 2.5ml beside the left sciatic nerve.The latency and nerve conduction velocity(NCV)of compound action potential of all sciatic nerves were measured by RM6240 biological signal acquisition and processing system at 7 time points which were before injection(T0),and 10min(T1),20min(T2),30min(T3),40min(T4),50min(T5),60min(T6)after administration respectively.Results: 1.In R group,the latency of compound action potential of sciatic nerve trunk was prolonged gradually with time,especially at the time point of 30 and 40 min after administration,compared with the time point of before administration,P(27)0.05.The nerve conduction velocity on sciatic nerve trunk was slowed down gradually with time,espcially at the time point of 30,50,and60 min after administration,compared with the time point before administration,P(27)0.05.2.In D group,the latency of compound action potential of sciatic nerve trunk was prolonged gradually with time,espcially at the time point of 50 and 60 min after administration,compared with the time point before administration,P(27)0.05.The nerve conduction velocity on sciatic nerve trunk was slowed down gradually with time,espcially at the time point of 50 and 60 min after administration,compared with the time point before administration,P(27)0.05.3.In RD group,the latency of compound action potential of sciatic nerve trunk was prolonged gradually with time,espcially at the time point of 40,50 and 60 min after administration compared with the time point before administration and at the time point of 50 and 60 min compared with the time point of 10 min after administration,P(27)0.05.The nerve conduction velocity on sciatic nerve trunk was slowed down gradually with time,espcially at the time point of 20,40,50 and 60 min after administration compared with the time point before administration and at the time point 50 and 60 min compared with the time point of 10 min after administration,P(27)0.05.4.The latency of compound action potential of sciatic nerve trunk in the four groups(R group,D group,RD group,and N group)was significantly different after administration.At the time point of 30 min after administration,the latency in R group was significantly longer than that in N group,P value was 0.003.At the time point of 40 min after administration,the latency in RD group and R group was significantly longer than that in R,D,and N group,P values were 0.007,0.013 and 0.015 respectively,the latency in R group was significantly longer than that in N group,P value was 0.003.At the time point of 50 min after administration,the latency in RD group was significantly longer than that in D and N group,P values were 0.005 and 0.015 respectively.At the time point of60 min after administration,the latency in RD group was significantly longer than that in D and N group,P values were 0.013 and 0.011 respectively.5.The nerve conduction velocity of sciatic nerve trunk in the four groups(R group,D group,RD group,and N group)was significantly different after administration.At the time point of 10 min after administration,the nerve conduction velocity in RD group was significantly slower than that in D and N group,P values were 0.050 and 0.011 respectively.At the time point of 20 min after administration,the nerve conduction velocity in RD group was significantly slower than that in D and N group,P values were 0.020 and 0.037 respectively,the nerve conduction velocity in R group was significantly slower than that in N group,P value was 0.044.At the time point of 30 min after administration,the nerve conduction velocity in R group was significantly slower than that in N group,P value was 0.014.At the time point of 40 min after administration,the nerve conduction velocity in RD group was significantly slower than that in R,D,and N group,P values were 0.007,0.005 and 0.010 respectively,the nerve conduction velocity in R group was significantly slower than that in N group,P value was 0.001.At the time point of 50 min after administration,the nerve conduction velocity in RD group was significantly slower than that in R,D,and N group,P values were 0.037,0.000 and 0.008 respectively,the nerve conduction velocity in R group was significantly slower than that in N group,P value was 0.003.At the time point of 60 min after administration,the nerve conduction velocity in RD group was significantly slower than that in R,D and N group,P values were 0.048,0.000 and 0.005,the nerve conduction velocity in R group was significantly slower than that in N group,P value was 0.007.Conclusion: 1.Perineural administration of dexmedetomidine can prolong the latency of compound action potential,and slow down the nerve conduction velocity of sciatic nerve trunk.2.Compared with administration of ropivacaine alone,perineural administration of ropivacaine combined with dexmedetomidine can significantly prolong the latency of compound action potential and slow down the nerve conduction velocity of rabbit sciatic nerve trunk.3.The effect of dexmedetomidine on prolonging the latency of compound action potential and slowing down the nerve conduction velocity of peripheral nerve may be one of the mechanisms of enhancing the nerve block effect of local anesthetics.