挥发性吸入麻醉药对短潜伏期体感诱发电位的影响

Effects of volatile anesthetics on short-latency somatosensory evoked potentials

目的 选择合适的吸入麻醉药及其浓度,为术中体感诱发电位（SSEP）监测提供参考。方法60例择期行神经外科手术的患者随机分成三组:安氟醚组、异氟醚组和地氟醚组。每个患者在清醒和挥发性麻醉药呼气末浓度分别为0.3、0.5、0.75、1.0和1.5MAC时记录正中神经体感诱发电位N13（颈髓）及N20（大脑皮层）。观察皮层电位N20、颈髓电位N13的潜伏期、波幅和中枢传导时间（CCT）的变化。结果 三种吸入麻醉药不改变皮层下电位N13的潜伏期和波幅（P>0.05）。而皮层电位N20的潜伏期和中枢传导时间（CCT）随安氟醚、异氟醚和地氟醚呼气末浓度的增加,逐渐延长,波幅则下降（P<0.05）。其中吸入安氟醚在呼出末浓度1.0MAC时有3例患者波形消失,在1.5MAC时共有6例患者波形消失,而异氟醚和地氟醚呼吸末浓度只在 1.5MAC时有3个患者波形消失。结论（1）挥发性吸入麻醉药对SSEP的皮层成分N20波潜伏期和波幅的影响呈浓度依赖性,对皮层下成分N13波影响轻微;（2）在三种吸入麻醉药中,安氟醚对皮层SSEP影响比异氟醚及地氟醚更大,而后两者作用相似。术中SSEP监测时,安氟醚在呼气末浓度不大于0.75MAC时是合适的;异氟醚、地氟醚在呼气末浓度不大于1.0MAC时是合适的。

ve In order to improve the reliability of somatosensory evoked potentials (SSEP) monitoring during anesthesia, we compared the effects of three commonly used volatile anesthetics on SSEP to choose suitable volatile anesthetic and determine the appropriate end-expiratory concentrations which have least effects on SSEP monitoring. Methods Sixty ASA I - II patients undergoing elective intracranial surgery were randomly divided into three groups: group A received enflurane; group B isoflurane and group C desflurane. The demographic data including age, body weight, height and sex were not significantly different between the three groups. In addition to SSEP, ECG, BP, SpO2, PET CO2 and end-tidal concentration of inhalation anesthetic were monitored. The SSEP electrodes were placed on N13 on the neck and N20 on the scalp. Before experiment the patient was asked to lie quietly for 10 min, then the patient started breathing 100% O2 and fresh-gas-flow (FGF) was set at 5 L/min. Median nerve on one side was stimulated and SSEP waves from cortex and cervical spinal cord were recorded as baseline tracing before anesthesia. The concentration of inhalation anesthetic was gradually increased from 0 to 0.3, 0.5, 0.75, 1.0 and 1.5 MAC. Each concentration was maintained for 15 min and SSEP waves were recorded. During experiment if the patient developed respiratory depression, oral airway was inserted and assisted ventilation was performed to maintain PETCO2 at 35-45minHg. If the patient developed hypotension, fluid was infused at an increased rate and vasopressor was given if necessary to maintain normal BP (baseline ± 20 % ) . Results The three volatile anesthetics did not change N13 latency and amplitude. Increasing concentrations of enflurane, isoflurane and desflurane were associated with graded reduction in N20 amplitude and increase in N20 latency and N13-N20 interpeak latency. Conclusions The results suggest (1) cortical SSEPs are moresensitive to the volatile anesthetics than subcortical SSEPs, (2) end-tidal concentration of enflurane less than 0.75 MAC is compatible with effective SSEP monitoring, whereas the end-tidal concentration of isoflurane or desflurane compatible with effective SSEP monitoring was less than 1.0 MAC. Enflurane has greater effect on SSEP than isoflurane and desflurane.