RESUMO
Objective To determine the optimum dose of dexmedetomidine administered locally through evaluating the effects of different doses of dexmedetomidine on the median effective concentration (EC50) of ropivacaine for brachial plexus block.Methods American Society of Anesthesiologists physical status Ⅰ or Ⅱ patients of both sexes, aged 19-50 yr, weighing 50-80 kg, scheduled for elective ulna and radius fracture open reduction and internal fixation, requiring ultrasound-guided axillary brachial plexus block, were randomly assigned into 4 groups using a random number table: control group (group C) and dexmedetomidine 0.4, 0.6 and 0.8 μg/kg groups (D1 , D2 and D3 groups).Axillary brachial plexus block was performed only with ropivacaine in group C.In D1-3 groups, axillary brachial plexus block was performed with the mixture of ropivacaine and dexmedetomidine 0.4, 0.6 and 0.8 μg/kg, respectively.The effective block was defined as complete loss of pain sensation in the areas innervated by the brachial plexus.The volume of local anesthetics was 40 ml.The concentration of ropivacaine was determined by up-and-down technique.The initial concentration was 0.4％ and the ratio between the two successive concentrations was 1.0.If the block was effective, the next patient received a lower dose of ropivacaine;or conversely if ineffective, a higher dose was given in the next patient.At least 7 independent crossover pairs were observed in each group.The EC50 of ropivacaine was the mean of the concentration of ropivacaine of each crossover pair.The occurrence of brachial plexus block-related adverse events, adverse cardiovascular events and over-sedation was recorded.Results In C, D1, D2 and D3 groups, 20, 22, 24 and 19 patientswere enrolled, respectively.Compared with group C, the EC50 of ropivacaine was significantly decreased in D2 and D3 groups, and no significant change in the EC50 of ropivacaine was found in group D1.No patients developed adverse events in group D1.The incidence of bradycardia was 17％, but it was transient in group D2.In group D3, the incidence of bradycardia and hypotension was 58％ and 32％, respectively, and they required special treatment, and the incidence of over-sedation was 10％.Conclusion The optimum dose of dexmedetomidine is 0.6 μg/kg when mixed with ropivacaine for brachial plexus block.
RESUMO
Objective To evaluate the role of MCP/DAF expression in the spinal cord in the development of neuropathic pain (NP) induced by chronic constrictive injury (CCI) of the sciatic nerve in rats.Methods Twenty-four Sprague-Dawley rats transfected with MCP/DAF,weighing 200-250 g,were randomly divided into 2 groups (n =12 each) using a random number table:sham operation of transfected rat group (Rsham group) and CCI of transfected rat group (RCCI group).Twenty-four healthy male Sprague-Dawley rats,weighing 200-250 g,were randomly divided into 2 groups (n =12 each) using a random number table:sham operation of normal rat group (Nsham group) and CCI of normal rat group (NCCI group).The right sciatic nerve was exposed and 4 loose ligatures wen placed on the sciatic nerve at 1 mm intervals with 4-0 catgut in RCCI and NCCI groups.The right sciatic nerve was only exposed in Rsham and Nsham groups.Paw withdrawal threshold to yon Frey filament stimulation (PWT) and paw withdrawal latency to nociceptive thermal stimulation (PWL) were measured at 1 day before operation (baseline) and 1,3 and 7 days after operation.The animals were sacrificed after measurement of pain threshold on 7 days after operation and the L4,5 segment of the spinal cord was removed for determination of the expression of OX-42 (by immuno-histochemistry) and MCP mRNA and DAF mRNA (by RT-PCR).Results Compared with Nsham group,the PWT and PWL were significantly decreased on 1,3 and 7 days after operation,the expression of OX-42 was up-regulated,and the expression of MCP mRNA and DAF mRNA was down-regulated in NCCI group (P ＜ 0.05),and no significant changes were found in the PWT and PWL on 1,3 and 7 days after operation and expression of OX-42(P ＞ 0.05),and the expression of MCP mRNA and DAF mRNA was up-regulated in Rsham and RCCI groups (P ＞ 0.05).Compared with NCCI group,the PWT and PWL were significantly increased on 1,3 and 7 days after operation,the expression of OX-42 was down-regulated,and the expression of MCP mRNA and DAF mRNA was up-regulated in RCCI group (P ＜ 0.05).Conclusion Up-regulation of MCP/ DAF expression in the spinal cord can inhibit the development of NP in rats and regulation of activation of microglias in the spinal cord is involved in the mechanism.