不同浓度七氟烷麻醉与不同刺激电压对脊髓手术中运动诱发电位波幅和潜伏期的影响

目的：评价七氟烷在不同呼气末浓度和不同刺激电压时对脊髓手术中运动诱发电位（motor evoked potentials，MEPs）监测的影响，为临床需要进行MEPs监测手术的麻醉用药提供选择依据。方法： 选择年龄18~65岁、ASA Ⅰ~Ⅱ级、需择期行胸腰段脊髓肿瘤切除手术的患者48例。常规全身麻醉（全麻）诱导后，在手术重要操作步骤开始前分别测定刺激电压为300 V、400 V、500 V、600 V时和七氟烷呼气末浓度分别为0.0%、0.5%、1.0%、1.5%时的MEPs波幅和潜伏期。全麻期间瑞芬太尼的输注速度维持在0.2 μg/（kg·min），适当调整丙泊酚泵注速度维持脑电双频谱指数（bispectral index，BIS）在30～50范围内。结果： 七氟烷呼气末浓度和电生理监测仪的刺激电压显著影响MEPs的波幅，在同一刺激电压下，随七氟烷呼气末浓度的提高，MEPs的波幅下降,呼气末浓度1.5%时MEPs波幅（左侧20.50 μV、70.71 μV、135.97 μV、190.00 μV，右侧14.29 μV、50.71 μV、73.10 μV、77.50 μV）明显低于呼气末浓度0.5%时MEPs波幅（左侧100.00 μV、362.57 μV、444.05 μV、435.00 μV ，右侧115.00 μV、207.15 μV、258.34 μV、358.50 μV）以及0.0%时MEPs波幅（左侧143.00 μV、388.10 μV、484.53 μV、500.00 μV，右侧176.00 μV、407.60 μV、384.35 μV、451.00 μV）， 差异有统计学意义（左侧χ2= 27.46, P< 0.01，右侧χ2=60.49, P< 0.01；左侧χ2= 20.73, P< 0.01，右侧 χ2=55.05,P< 0.01；左侧χ2= 34.25,P< 0.01，右侧χ2=33.58,P< 0.01； 左侧χ2= 28.61,P< 0.01，右侧 χ2= 49.04,P< 0.01）；MEPs的潜伏期也有延长，但结果差异无统计学意义（P=0.26）。同一呼气末浓度下，随刺激电压的增大，MEPs波幅增高，电压300 V时MEPs波幅（左侧 143.00 μV、100.00 μV、61.50 μV、20.50 μV，右侧176.00 μV、115.00 μV、41.07 μV、14.29 μV）明显低于400 V时MEPs波幅（左侧388.10 μV、362.57 μV、198.81 μV、70.71 μV，右侧407.60 μV、207.15 μV、89.00 μV、50.71 μV）、500 V时MEPs波幅（左侧484.53 μV、444.05 μV、216.24 μV、135.97 μV，右侧 384.35 μV、258.34 μV、187.50 μV、73.10 μV）与600 V时MEPs波幅（左侧500.00 μV、435.00 μV、344.00 μV、190.00 μV，右侧451.00 μV、385.50 μV、156.00 μV、77.50 μV）， 差异有统计学意义（左侧χ2= 45.55,P< 0.01，右侧χ2= 25.73,P< 0.01；左侧χ2= 46.67,P< 0.01，右侧χ2= 55.30,P< 0.01；左侧χ2= 47.36,P< 0.01， 右侧χ2= 47.82,P< 0.01；左侧χ2= 38.67,P< 0.01 ，右侧χ2= 45.87,P< 0.01）。同一呼气末浓度下，随刺激电压的增大，MEPs的潜伏期逐渐缩短，电压300 V时MEPs潜伏期与400 V、500 V、600 V MEPs潜伏期比较差异有统计学意义（左侧 F=7.50，P=0.01；右侧F=13.33，P<0.01），但是这种潜伏期的变化没有临床意义。同一刺激电压下，随七氟烷呼气末浓度的提高，MEPs的成功率下降，呼气末浓度1.5%时MEPs的成功率(左侧43.8%、70.8%、77.1%、81.3%，右侧37.5%、60.4%、75.0%、66.7%)明显低于呼气末浓度0.5%时MEPs的成功率（左侧72.9%、89.6%、95.8%、95.8%，右侧66.7%、89.6%、95.8%、97.9%）及0.0%时MEPs的成功率（左侧79.2%、87.5%、95.8%、93.8% ，右侧75.0%、95.8%、95.8%、95.8%）， 而同一呼气末浓度下，增大刺激电压可以提高MEPs的成功率，电压300 V时MEPs的成功率（左侧79.2%、72.9%、62.5%、43.8%，右侧75.0%、66.7%、60.4%、37.5%）明显低于400 V MEPs的成功率（左侧87.5%、89.6%、77.1%、70.8%，右侧95.8%、89.6%、79.2%、60.4%）、500 V MEPs的成功率（95.8%、95.8%、91.7%、77.1%，右侧95.8%、95.8%、81.3%、75.0%）以及600 V时MEPs的成功率（左侧93.8%、95.8%、89.6%、81.3%，右侧95.8%、97.9%、89.6%、66.7%），刺激电压600 V、七氟烷呼气末浓度为1.5%时MEPs的成功率与刺激电压300 V、七氟烷呼气末浓度为0.0%时MEPs的成功率差异无统计学意义（P=0.22）。结论： 七氟烷对术中MEPs监测具有剂量依赖性抑制作用，但通过增加刺激电压，可以增大MEPs的波幅，缩短MEPs的潜伏期，提高MEPs监测的成功率，扩大了七氟烷在脊髓功能监测手术中的适用范围。

Influence of sevoflurane concentration and stimulation voltage on motor evoked potentials in intraspinal tumor surgery

Objective:To evaluate the effects of increasing end-tidal concentrations of sevoflurane and increasing stimulation voltage on motor evoked potentials,so as to provide evidence in making anesthesia plan for intraspinal tumor surgery.Methods:In the study,48 patients scheduled to undergo intraspinal tumor surgery [American Society of Anesthesiology,(ASA)Ⅰ-Ⅱ,18-65 years old]were enrolled. After general anesthesia induction,the patients were assigned to receive sevoflurane anesthesia of increa-sing end-tidal concentration in the sequence of 0.0%,0.5%,1 .0% and 1 .5% respectively,under a background of propofol and remifentanil.All the observations were done before the important steps of sur-gery.Remifentanil infusion rate was 0.2 μg /(kg·min),while the propofol infusion rate was adjusted to maintain the bispectral index values within the range of 30-50.At each concentration,4 stimulation voltages of 300 V,400 V,500 V and 600 V were employed to elicit motor evoked potentials (MEPs). The amplitude and latency of each MEP were compared.The success ratio was also recorded.Results:The concentration of sevoflurane and the stimulation voltage had impacts on the amplitude and latency of MEPs.Under each stimulation voltage,the MEPs amplitude decreased following increasing end-tidal sevoflurane concentrations,and significant differences were found in comparing 1 .5% sevoflurane (left 20.50 μV,70.71 μV,135.97 μV,190.00μV ,right 14.29 μV,50.71 μV,73.10μV,77.50μV) with 0.0% sevoflurane (left 143.00 μV,388.10 μV,484.53 μV,500.00 μV,right 176.00 μV, 407.60 μV,384.35 μV,451.00 μV)and 0.5% sevoflurane (left 100.00 μV,362.57 μV,444.05μV,435.00 μV,right 115.00 μV,207.15 μV,258.34 μV,358.50 μV),left χ2 =27.46,P<0.01,right χ2 =60.49,P<0.01;left χ2 =20.73,P<0.01,right χ2 =55.05,P<0.01;left χ2 =34.25,P<0.01,right χ2 =33.58,P<0.01;left χ2 =28.61,P<0.01 ,right χ2 =49.04,P<0.01;while there were no statistical differences in the latency changes (P =0.26 ).Under each end-tidal sevoflurane concentration,the MEPs amplitude increased following increasing stimulation voltages,and significant differences were found in comparing 300 V (left 143.00 μV,100.00 μV,61.50 μV,20.50μV ,right 176.00 μV,115.00 μV,41.07 μV,14.29 μV)with 400 V (left 388.10 μV,362.57μV,198.81 μV,70.71 μV,right 407.60 μV,207.15 μV,89.00 μV,50.71 μV)and 500 V (left 484.53 μV,444.05 μV,216.24μV,135.97 μV,right 384.35 μV,258.34μV,187.50μV,73.10μV)and 600 V (left 500.00 μV,435.00 μV,344.00 μV,190.00 μV,right 451.00 μV,385.50μV,156.00μV,77.50μV),leftχ2 =45.55,P<0.01,rightχ2 =25.73,P<0.01;leftχ2 =46.67, P<0.01,right χ2 =55.30,P<0.01;left χ2 =47.36,P<0.01,right χ2 =47.82,P<0.01;left χ2 =38.67,P<0.01,right χ2 =45.87,P<0.01;while the latencies were decreased,and significant dif-ferences were found in comparing 300 V with 400 V and 500 V and 600V(left F=7.50,P=0.01 ,right F=13.33,P<0.01),but the differences had little clinical significance.The success ratio decreased by increasing end-tidal sevoflurane concentration,and significant differences were found in comparing 1 .5%sevoflurane (left 43.8%,70.8%,77.1%,81.3%,right 37.5%,60.4%,75.0%,66.7%)with 0.0%sevoflurane (left 79.2%,87.5%,95.8%,93.8%,right 75.0%,95.8%,95.8%,95.8%)and 0.5%sevoflurane (left 72.9%,89.6%,95.8%,95.8%,right 66.7%,89.6%,95.8%,97.9%);the suc-cess ratio increased by increasing stimulation voltage,and significant differences were found in comparing 300 V(left 79.2%,72.9%,62.5%,43.8%,right 75.0%,66.7%,60.4%,37.5%)with 400 V(left 87.5%,89.6%,77.1%,70.8% ,right 95.8%,89.6%,79.2%,60.4%)and 500 V(left 95.8%, 95 .8%,9 1 .7%,77 .1%,right 95 .8%,95 .8%,8 1 .3%,75 .0%)and 600 V (left 93 .8%,95 .8%, 89.6%,81.3%,right 95.8%,97.9%,89.6%,66.7%),but there were no statistical differences in the success ratio of MEPs between the group with stimulation voltage of 600 V ,end tidal sevoflurane concen-tration of 1 .5% and the group with stimulation voltage of 300 V,end tidal sevoflurane concentration of 0.0% (P=0.22).Conclusion:Sevoflurane inhibited MEPs in a dose-dependent manner.It can de-crease the amplitudes and prolong the latencies.But increasing stimulation voltage will facilitate MEPs monitoring and increase the success ratio.Sevoflurane can be used in larger parts of MEPs monitoring surgery by increasing the stimulation voltage.