Porkkala T, Kaukinen S, Häkkinen V, Jäntti V
International Graduate School in Neurosciences, University of Tampere, Finland.
Can J Anaesth. 1997 Sep;44(9):963-8. doi: 10.1007/BF03011968.
The effect of isoflurane on the subcortical P14 component of the median nerve somatosensory evoked potential (SEP) is poorly known. We studied whether the P14 wave from the upper brainstem, recorded with a nasopharyngeal electrode, was attenuated at the isoflurane-induced EEG burst-suppression level. We also compared the effect of isoflurane on the P14, cervical N13 and cortical N20, N35 and N6, components.
Seventeen elective patients were anaesthetized with isoflurane. Somatosensory evoked potentials were recorded prior to anaesthesia, at 0.5 MAC and 1 MAC end-tidal isoflurane as well as at the level when EEG was in burst-suppression (mean 1.9 vol% end-tidal isoflurane).
Isoflurane had varying effects on the subcortical components of median SEP. The amplitude of nasopharyngeal P14 was stable, but the mean latency increased from 14.4 +/- 1.2 msec at 0.5 MAC to 15.2 +/- 1.1 msec at burst-suppression level (P < 0.05). In contrast, the N13 neck response amplitude was attenuated from 3.3 +/- 0.6 microV to 2.6 +/- 0.5 microV (P < 0.005) without latency changes. The latency of the cortical N20 wave was increased from 19.7 +/- 1.1 msec at awake to 24.4 +/- 1.6 msec at burst-suppression level (P < 0.0001) and amplitude was reduced from 3.3 +/- 1.1 microV to 1.3 +/- 0.6 microV (P < 0.0001). The later cortical components were attenuated even during 0.5 MAC isoflurane and were not recordable during EEG burst-suppression.
We conclude that P14 can reliably be recorded with nasopharyngeal electrodes during isoflurane anaesthesia, even during EEG burst-suppression, when the N20 wave is attenuated. In contrast, the middle-latency SEP components are sensitive to isoflurane anaesthesia.
异氟烷对正中神经体感诱发电位（SEP）皮层下P14成分的影响尚不清楚。我们研究了使用鼻咽电极记录的来自脑桥上部的P14波在异氟烷诱导的脑电图爆发抑制水平时是否衰减。我们还比较了异氟烷对P14、颈部N13以及皮层N20、N35和N6成分的影响。
17例择期手术患者接受异氟烷麻醉。在麻醉前、呼气末异氟烷浓度为0.5MAC和1MAC时以及脑电图处于爆发抑制状态（呼气末异氟烷平均浓度1.9%）时记录体感诱发电位。
异氟烷对正中神经SEP的皮层下成分有不同影响。鼻咽部P14的波幅稳定，但平均潜伏期从0.5MAC时的14.4±1.2毫秒增加到爆发抑制水平时的15.2±1.1毫秒（P<0.05）。相比之下，N13颈部反应波幅从3.3±0.6微伏衰减到2.6±0.5微伏（P<0.005），潜伏期无变化。皮层N20波的潜伏期从清醒时的19.7±1.1毫秒增加到爆发抑制水平时的24.4±1.6毫秒（P<0.0001），波幅从3.3±1.1微伏降低到1.3±0.6微伏（P<0.0001）。甚至在呼气末异氟烷浓度为0.5MAC时，较晚的皮层成分就已衰减，在脑电图爆发抑制期间无法记录。
我们得出结论，在异氟烷麻醉期间，即使在脑电图爆发抑制、N20波衰减时，使用鼻咽电极也能可靠地记录P14。相比之下，中潜伏期SEP成分对异氟烷麻醉敏感。
