| Objective: To study effects of tetracaine and ropivacaine upon the function and morphology of brachial plexus nerve trunks of rats. To evaluate the security of different concentrations tetracaine and ropivacaine on nerve blockade and provide a basis for clinical medicine.Methods: Forty-eight, active, adult, male SD rats weighing about 405～435g ,from Nanchang University School of Medicine Laboratory Animal Center, were randomly were randomly divided into 3 groups: group NS (normal saline as control),group tetracaine,group ropivacaine.Then the three groups were randomly divided into 8 groups (6 each): group NS,group D1,group D2,group D3,group R1,group R2,group R3,group R4 administered respectively 0.9%saline 1 ml,0.25%tetracaine 0.5 ml,0.5%tetracaine 0.5 ml,1%tetracaine0.5 ml,0.25%ropivacaine 1 ml,0.5%ropivacaine 1 ml,1%ropivacaine 1 ml ,2%ropivacaine 0.5 ml.One side of brachial plexus nerve was perfused drugs, the other side was as control consubstantiality.Five days later,compound action potential (AP)of the brachial plexus nerve trunks was made to observe the changes of maximum amplitude and conduction velocity(NCV), and in light microscopy and transmission electron microscope the morphological changes was to be observed.Results:1. The maximum amplitude of injection side in group D1～3 is 3.82±0.4 mv,2.56±0.60 mv,1.76±0.59 mv respectively,and conduction velocity 19.35±1.15 m/s,16.71±1.20 m/s,14.81±1.57 m/s respectively. Comparing with the control side and saline control group, there was no significant difference in group D1(P>0.05), but lowering of the maximum amplitude, slowing of NCV was distinct in group D2～3(P<0.05);In tetracaine groups:comparing with group D1, lowering of the maximum amplitude, slowing of NCV was obvious in group D2～3;Comparing with group D2, lowering of the maximum amplitude, slowing of NCV was obvious in group D3(P<0.05).2. The maximum amplitude of injection side in group R1～4 is 3.52±0.43 mv,3.44±0.55mv,3.09±0.68 mv,2.18±0.65mv respectively,and conduction velocity 19.31±1.13 m/s,18.67±1.17 m/s,18.00±1.22 m/s,15.71±1.64 m/s respectively. Comparing with the control side and saline control group, there was no significant difference in group R1～2(P>0.05), but lowering of the maximum amplitude, slowing of NCV was obvious in group R3～(4P<0.05);in ropivacaine groups:comparing with injection side of group R1～3, lowering of the maximum amplitude, slowing of NCV was obvious in group R4(P<0.05).3. Comparing equivalent dose group tetracaine with group ropivacaine,there was no significant difference in group D1(P>0.05), lowering of the maximum amplitude, slowing of NCV was obvious in group D2～3(P<0.05).4. In microscope,the structure of nerve fibers were normal in group D1,group R1～2;the phenomenon of perineurium edema was found in group R3;there were swelling of perineurium obviously and myelin sheath incrassation and axonal lessening relatively and dispersed nerve fiber as a result of edema in group D2～3,group R4. In transmission electron microscope,there were no obvious changes of the early ultrastructur of brachial plexus nerve trunks in group D1,group R1～2;the phenomenon of demyelination was found in group R3;the phenomenon of myelin lamellar separation, fracture, demyelinating , axonal atrophy and swelling of mitochondria within the axon was found in group D2～3,group R4.Conclusion: 1.Five days after injection, 0.5%,1% tetracaine and 1%,2%ropivacaine may be injurious to the function of brachial plexus nerve trunks;2. The extent of damage was in matter of the concentration of tetracaine and ropivacaine;3,The harm of equivalent dose tetracaine is more significant than that of ropivacaine.4. The mechanism about the harm of tetracaine and ropivacaine brachial plexus nerve function was relevant to the brachial plexus pathomorphology change of demyelination, axonal atrophy, mitochondrial swelling. |
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