吸入麻醉药对短潜伏期体感诱发电位和脑电双频指数监测的影响

目的在脑电双频指数（BIS）监护下,为术中短潜伏期体感诱发电位（SSEP）监护选择合适的吸入麻醉药物和浓度。方法60例神经外科择期手术患者随机分成安氟烷、异氟烷和地氟烷组,每组20例,按呼气末浓度为0．3、0．5、0．75、1．0和1．5最低肺泡有效浓度（MAC）时分别吸入不同浓度的麻醉药,记录皮层SSEP的N20波幅、潜伏期,并同时进行BIS监护,观察3种吸入麻醉药在不同吸入浓度下对SSEP和BIS的影响。结果随着吸入浓度的增加,所有3组SSEP的N20波幅逐渐下降,潜伏期逐渐延长。其中在呼气末浓度1．0MAC时,异氟烷和地氟烷组的N20波幅下降已经超过50％,安氟烷组有3例波形消失;而在1．5MAC时,异氟烷和地氟烷组分别有3例的N20波形消失,安氟烷组共有6例波形消失。BIS监测发现在1．0MAC时,各组的BIS值均在60以下,而在0．75MAC时,安氟烷组（BIS值：45～64）和地氟烷组（44～61）仍有部分患者的BIS值高于60,而异氟烷组BIS值均在60以下（39～58）。皮层SSEP波幅和潜伏期与BIS值之间没有良好的相关性。结论挥发性吸入麻醉药对BIS和皮层SSEP的影响成剂量相关性。在合适的麻醉深度下,选择0．75MAC的异氟烷更适合术中皮层SSEP监护。尽管挥发性吸入麻醉药对EEG和SSEP的影响分别与其作用于大脑皮层有关,但二者之间相关性较差。

Effects of volatile anesthetics on cortical somatosensory evoked potential and Bispectral index

OBJECTIVE: To improve the anesthetic environment in monitoring short-latency somatosensory evoked potentials (SSEP) during operation, we compared the effects of different anesthetics on SSEP and Bispectral index (BIS), which aim to select suitable anesthetics and their doses used intraoperatively. METHODS: 60 ASA I-II patients undergoing elective neurosurgery were randomly allocated into three groups: enflurane, isoflurane and desflurane group. The concentration of each volatile anesthetic was increased step by step from 0 to end-tidal 0.3, 0.5, 0.75, 1.0 and 1.5 MAC. The changes of cortical SSEP component N20 were recorded as well as Bispectral index (BIS) monitoring. The effects of three volatile anesthetics in various concentrations on short-latency SSEP and BIS were investigated. RESULTS: All three volatile anesthetics significantly decreased N20 amplitude and prolonged N20 latency. The N20 waveform disappeared in some patients when the end-tidal concentration of enflurane reached 1.0 MAC, it occurred when that of isoflurane or desflurane was at 1.5 MAC. BIS monitoring showed BIS values were all under 60 when at 1.0 MAC in three group. For some patients in enflurane group and desflurane group, BIS values were above 60 (45-64, 44-61, respectively) when at 0.75 MAC, while those in isoflurane group were still less than 60 (39-58). And the amplitude or latency of cortical SSEP correlated poorly with BIS. CONCLUSION: The effects of three volatile anesthetics on SSEP and BIS are significant in dose-dependent manner. Anesthetic regimen of 0.75 MAC isoflurane for intraoperative cortical SSEP monitoring may be optimal. It seemed that the correlation between BIS and short-latency SSEP was poor, although both are associated with the effects of anesthetics on cerebral cortex.