| Objective: the study was disigned to use ethology and cellular pathology to assess the effectiveness and safety of dexmedetomidine added to ropivacaine for the continuous femoral nerve block.Methods: 30 healthy New Zealand rabbits,weight: about 2~3kg,male and female was unlimited.The animals will be divided into 5 groups by a computer-generated random number sequence(n=6).the control group A is received normal saline,group B received 0.25% ropivacaine;group C received0.25% ropivacaine+1?g/ml dexmedetomidine;group D received 0.25%ropivacaine +2?g/ml dexmedetomidine;group E received 0.25% ropivacaine+3?g/ml dexmedetomidine;Animal model :Place the epidural catheter next to the lower limb femoral nerve.the Concentration of 5% formalin 0.5ml was injected to the subcutaneous of the patella in knee joint.The continuous analgesia pump was connected to the catheter after the completion of the animal experimental model.Parameter setting: the background dose is 1ml drug,continue dose :0.5ml/h;A single additional injection of 1 ml drug every 6 hours.Observe indicators:1.animal behavioral score(zero: The injected leg was able to load,and there is no significant difference when compared with the injected legand normal leg.1 score: the injected legs almost can not load,a clear limp can be seen in the movement.2 scores : the injected leg was raised,and can not load.3 scores: Scratching,licking bite or shaking into the leg.2.analgesic onset time: immediately after the pain caused to resume normal rabbit walking time.3.quantitative analysis of myelin area of femoral nerve.4.observation of nerve cell structure by transmission electron microscopy.Observing animals behavior performance and scored,T0(after the formalin was injected to the subcutaneous of the patella in knee joint)T1(background dose injection for 2hours),T2(a single additional injection for the first time)and T3(a single additional injection for the fourth time),formalin was injected to the subscutaneous of the patella in knee joint in front of the assessment.48 hours after administration of drugs,rabbits were sacrificed and the femoral nerve were removed for pathological investigation.We make a quantitative analysis to the area of myelin sheath by using image analyzer system.Observing the epineurium,the bunch of membrane and inner membrance by using light microscope.In addition,we use the transmission electron microscope(TEM)to observe the change of myelin sheath and other superfine cellular structure.Results :there were significant differences in the behavioral score when compared with group A and group B,group C,group D and group E at time T1 and time T2(P<0.05).There was no apparent differences between group B and group C at time T1 and T2(P>0.05),while the differences were considered to be significant at P<0.05 when compared group D with group E.There were significant differences in the comparison of bebavioral score when compared with group A and group B,group C,group D,group E at time T1 and T2.(p<0.05).there was no apparent differences between group B and group C at time T1 and T2(P>0.05),while the differences were considered to besignificant at p<0.05 when compared group D with group E.There were significant differences when compared with group C and group D,group E(P<0.05).The recovery time takes longer when compared with group A and group B,group C,group D and group E(p<0.05).There was no apparent differences between group B and group C(P>0.05),The time needed to restore the walk takes longer when compared with group C and group D,group E(P<0.05).However,there was no apparent differences between group D and group E(P>0.05).The quantitative analysis of myelin sheath area under light microscope announce that there was no apparent differences among all the groups and the myelin sheath and other ultra structural electron microscope results also showed that there was no apparent differences among all the groups.Conclusion: There were significant differences when compared with group C and group D,group E(p<0.05).The quantitative analysis of myelin sheath area under light microscope announce that there was no apparent differences among all the groups.Myelin sheath and other ultra-structural electron microscopy announce that there was no demyelinating change in the groups A,groups B,groups C and groups D.However we can see there was demyelinating change in the groups E.Conclusion: Dexmedetomidine can strengthen the effect of analgesia and shorten the work time when added to ropivacaine applied in the continuous femoral nerve block.However,high concentrations of dexmedetomidine(3?g/L)combined with ropivacaine applied in the continuous femoral nerve block may cause never damage. |
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