Szelényi Andrea, Kothbauer Karl F, Deletis Vedran
Department of Neurosurgery, Klinikum der Johann Wolfgang Goethe Universität, Frankfurt/Main, Germany.
Clin Neurophysiol. 2007 Jul;118(7):1586-95. doi: 10.1016/j.clinph.2007.04.008. Epub 2007 May 15.
To evaluate the efficacy of constant current transcranial electric stimulation (TES) parameters for eliciting muscle motor evoked potentials (MEPs) in the abductor pollicis brevis muscles (APB) and the tibialis anterior muscles (TA). The following parameters were tested intraoperatively: interstimulus interval (ISI), individual stimulation pulse duration within a train of five stimuli. Different montages of stimulating electrodes were assessed for effectiveness and focality. Further, reference values for APB and TA motor thresholds in neurosurgical patients with normal motor status under total intravenous anesthesia were determined.
Motor thresholds of contralateral muscle MEPs were determined at 0.1, 0.2, 0.4, and 0.5 ms pulse duration and ISIs of 2, 3, 4, and 5 ms using a train of five monophasic constant current pulses with C3/C4 (27 patients). The stimulating electrodes were positioned at C1, C2, C3, C4, Cz, and Cz+6 cm. Different montages were used to determine the most effective and the most focal stimulation montages for the APB and TA muscles (30 patients). Eighty-six patients with clinically normal motor function were studied for motor threshold reference values.
The prolongation of the pulse duration has the strongest effect to decrease the motor threshold, which proportionally increases the delivered charge. The lowest stimulation threshold to elicit muscle MEPs in the APB and TA muscles is achieved with a train of stimuli consisting of an individual stimulus pulse duration of 0.5 ms. An ISI of 4 ms gave the lowest motor thresholds, but did not reach statistical significance compared to 3 ms. The stimulating electrode montage C3/C4 (C4/C3) allows for the lowest stimulation thresholds, but the vigorous muscle contractions it has is a disadvantage. The most focal stimulating electrode montages for the contralateral APB muscles are C3/Cz and C4/Cz, respectively, and for the TA muscles Cz/Cz+6 cm.
In adult neurosurgical patients with a normal motor status under total intravenous anesthesia, an individual pulse duration of 0.5 ms and an ISI of 4 ms provide the lowest motor thresholds. Pragmatically, C1/C2, resp., C2/C1 montage provides monitorable responses in both APB and TA muscles at reasonable stimulation thresholds without inducing movements disturbing surgery and especially microdissection. If the most focal hemispheric stimulation for the distal upper extremity muscles is required, the use of C3 or C4 referenced to Cz is recommended.
The stimulation parameters within a train of five pulses with an individual pulse duration of 0.5 ms and an ISI of 4 ms provide the lowest motor threshold. These data confirm not only studies for D wave recovery but also provide optimal stimulation parameters for intraoperative near threshold stimulation.
评估恒流经颅电刺激（TES）参数在诱发拇短展肌（APB）和胫前肌（TA）肌肉运动诱发电位（MEP）方面的效果。术中测试了以下参数：刺激间隔（ISI）、五个刺激脉冲序列中的单个刺激脉冲持续时间。评估了不同刺激电极组合的有效性和聚焦性。此外，还确定了在全静脉麻醉下运动状态正常的神经外科患者中APB和TA运动阈值的参考值。
使用五个单相恒流脉冲序列，在脉冲持续时间为0.1、0.2、0.4和0.5毫秒以及ISI为2、3、4和 5毫秒的情况下，测定对侧肌肉MEP的运动阈值（27例患者）。刺激电极位于C1、C2、C3、C4、Cz和Cz + 6厘米处。使用不同的组合来确定对APB和TA肌肉最有效和最聚焦的刺激组合（30例患者）。对86例运动功能临床正常的患者进行了运动阈值参考值研究。
脉冲持续时间的延长对降低运动阈值的影响最强，这会按比例增加传递的电荷量。在APB和TA肌肉中诱发肌肉MEP的最低刺激阈值是通过单个刺激脉冲持续时间为0.5毫秒的刺激序列实现的。ISI为4毫秒时运动阈值最低，但与3毫秒相比未达到统计学显著性。刺激电极组合C3/C4（C4/C3）的刺激阈值最低，但其引发的强烈肌肉收缩是一个缺点。对侧APB肌肉最聚焦的刺激电极组合分别是C3/Cz和C4/Cz，TA肌肉是Cz/Cz + 6厘米。
在全静脉麻醉下运动状态正常的成年神经外科患者中，单个脉冲持续时间为0.5毫秒和ISI为4毫秒可提供最低的运动阈值。实际上，C1/C2或C2/C1组合在合理的刺激阈值下能在APB和TA肌肉中提供可监测的反应，而不会诱发干扰手术尤其是显微解剖的运动。如果需要对远端上肢肌肉进行最聚焦的半球刺激，建议使用以Cz为参考的C3或C4。
五个脉冲序列中单个脉冲持续时间为0. 5毫秒和ISI为4毫秒的刺激参数可提供最低的运动阈值。这些数据不仅证实了关于D波恢复的研究，还为术中近阈值刺激提供了最佳刺激参数。
