神经刺激电流阈值取决于组织电阻抗：有关超声引导下正中神经电刺激的研究

背景了解影响神经电刺激所需电流阈值差异的相关机制，有助于提高周围神经阻滞的成功率和安全性；神经周围组织的电阻可能影响该神经对电刺激的反应。本项志愿者研究旨在探讨电阻与BI起神经肌肉反应所需电流阈值的关系。方法29例志愿者，在肘窝和腋窝分别进行正中神经电刺激和电阻测量。经超声定位，电刺激针针尖分别置于距离神经5、2．5、0mm处。电刺激波宽为0．1、0．3毫秒。结果当电刺激探针针尖距离神经分别为5mm和2．5mm时，肘部神经周围组织的电阻值与电流阈值存在着显著的负相关性（P值分别为0．001和0．036）。腋窝神经周围组织的电阻值（平均21．1Ω，标准差9．7Ω）明显低于肘部（平均36．6Ω，标准差13．412，P〈0．001），而在腋窝处的神经刺激电流阈值显著高于肘部（P〈0．001，P〈0．001，P=0．024）。波宽0．1毫秒和0．3毫秒时电流阈值测定值比值的均数为1．82。结论本研究表明，电流阈值与电阻存在负相关，应根据不同组织类型调整电流设置，且研究结果的临床意义有待进一步研究。

BACKGROUND： Understanding the mechanisms causing variation in current thresholds for electrical nerve stimulation may improve the safety and success rate of peripheral nerve blocks. Electrical impedance of the tissue surrounding a nerve may affect the response to nerve stimulation. In this volunteer study, we investigated the relationship between impedance and current threshold needed to obtain a neuromuscular response. METHODS： Electrical nerve stimulation and impedance measurements were performed for the median nerve in the axiUa and at the elbow in 29 volunteers. The needletip was positioned at a distance of 5, 2.5, and 0 mm from the nerve as judged by ultrasound. Impulse widths of 0. 1 and 0. 3 ms were used for nerve stimulation. RESULTS： A significant inverse relationship between impedance and current threshold was found at the elbow, at nerve-to-needle distances of 5 and 2.5 mm （P = 0.001 and P = 0. 036）. Impedance values were significantly lower in the axilla （mean 21.1, sd 9.7 kohm） than at the elbow （mean 36.6, SD 13.4 kohm） （P 〈 0. 001 ）. Conversely, current thresholds for nerve stimulation were significantly higher in the axilla than at the elbow （P 〈 0.001, P 〈 0. 001, P = 0. 024）. A mean ratio of 1.82 was found for the measurements of current thresholds with 0. 1 versus 0.3 ms impulse duration. CONCLUSIONS： Our results demonstrate an inverse relationship between impedance measurements and current thresholds and suggest that current settings used for nerve stimulation may require adiustment based on the tissue type. Further studies should be performed to investigate the clinical impact of our findings.