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准确地监测病人术中麻醉深度具有重要的临床意义,特别是现代复合麻醉技术的应用给医生判断麻醉深度带来了更大的困难。迄今为止,仍然没有一个客观、简便且准确的监测麻醉深度的方法。针对这一问题,本文通过分组动物实验,研究了芬太尼对猫中潜伏期听觉诱发电位(MLAEP)的影响,以探讨用诱发电位作为麻醉监测手段的可能性,并为临床提供有效、客观监测指标。将21只猫随机等分成三组:A组高浓度芬太尼组、B组空白对照组和C组低浓度芬太尼组。用苯巴比妥钠镇静之后,给肌松药并插管人工控制呼吸。芬太尼或等量生理盐水分三次由静脉注射,每次间隔20min,给总量的1/3。在给药前及每次给药后5min和15min时分别记录左右耳MLAEP,模拟信号频率范围10～250Hz,描记后经数字化送入计算机。记录电极置于头顶,左右耳后为参考。由波宽100μs的方波送入耳机产生短声刺激,刺激频率9.7次/s,刺激强度90dB听力级。MLAEP扫描时间50ms,迭加次数512次。数字信号采样率1.28kHz。A组动物在每次记录MLAEP的同时采动脉血样以测室血中芬太尼含量。随机选取9只动物做血气分析。实验过程中监测动物动脉血压及体温并维持恒定。首先,分析了芬太尼对猫MLAEP时域特性,即Na、Pa潜伏期和Pa幅值的影响。之后,用参数模型(11阶AR模型)方法做MIAEP信号的功率谱估计,研究了芬太尼对猫MLAEP信号谱峰位置的影响。进而,利用所建立的参数模型,提取5阶AR模型的系数、模型极点分布等特征量,寻找能准确反映麻醉深度的客观指标。经过组内分析和组间比较,得出:1.芬太尼对猫MLAEP的Na、Pa潜伏期及Pa幅值没有显著影响。2.芬太尼对猫MLAEP信号的功率谱谱峰位置没有显著影响。3.猫MLAEP信号的AR模型系数|A_1|和模型极点分布复平面上“小幅角”θ的大小随猫血中芬太尼浓度的增加明显减小。上述结果表明,本文所提出的MLAEP信号的AR模型特征量可以比其时域特性更敏感地反映芬太尼的作用,因此当芬太尼的用量与麻醉深度的关系建立以后,可以作为监测麻醉深度的客观指标。我们建议临床上利用MLAEP监测麻醉深度时,应同时考虑其时域和频域的多种参量,以确保判断结果的可靠性。
Accurately monitoring the depth of anesthesia in patients has important clinical significance, especially the application of modern composite anesthesia technology to the doctor to determine the depth of anesthesia brought greater difficulties. So far, there is still no objective, simple and accurate method of monitoring the depth of anesthesia. In response to this problem, we studied the effect of fentanyl on latent auditory evoked potentials (MLAEP) in cats by grouping animal experiments to explore the possibility of using evoked potential as a means of anesthesia monitoring and provide an effective and objective monitoring index. 21 cats were randomly divided into three groups: A group of high concentration fentanyl group, B group blank control group and C group of low concentration fentanyl group. After sedation with phenobarbital, muscle relaxants and cannulas are manually controlled for respiration. Fentanyl or an equal amount of normal saline three times by intravenous injection, each interval of 20min, to the total 1/3. The left and right ear MLAEP were recorded before administration and 5 min and 15 min after each administration, respectively. The simulated signal frequency range was 10 ~ 250 Hz. The data were digitized and sent to the computer. Recording electrode placed on the head, left and right ears for reference. By the wave width of 100μs square wave into the headset to produce short-sound stimulation, the stimulation frequency 9.7 times / s, stimulation intensity 90dB listening level. MLAEP scan time 50ms, the number of superposition 512 times. Digital signal sampling rate 1.28kHz. Animals in Group A received arterial blood samples simultaneously for MLAEP recording to measure fentanyl content in the blood samples. Nine animals were randomly selected for blood gas analysis. During the experiment, arterial blood pressure and body temperature were monitored and maintained constant. First, the effects of fentanyl on the temporal profile of cat MLAEP, namely the Na, Pa latency and Pa amplitude, were analyzed. After that, the parametric model (11th order AR model) was used to estimate the power spectrum of MIAEP signal, and the effect of fentanyl on the peak position of cat MLAEP signal was studied. Furthermore, the parameters of the fifth-order AR model are extracted, and the feature parameters of the model and the pole distribution are extracted to find the objective index that can accurately reflect the depth of anesthesia. After intra-group analysis and comparison between groups, we concluded that: 1. Fentanyl had no significant effect on the Na, Pa latency and Pa amplitude of MLAEP in cats. Fentanyl had no significant effect on the peak position of the power spectrum of MLAEP. 3. The AR model coefficient | A_1 | of the cat MLAEP signal and the “small angle” θ of the pole distribution on the complex plane of the model significantly decrease with the increase of fentanyl concentration in the feline blood. The above results show that the characteristics of the AR model proposed in this paper can reflect the effect of fentanyl more sensitively than the time-domain characteristics. Therefore, when the relationship between the dosage of fentanyl and the depth of anesthesia is established, it can be used as a monitoring anesthesia Objective indicators of depth. We suggest that the clinical use of MLAEP to monitor the depth of anesthesia, it should also consider the time and frequency domain of a variety of parameters to ensure the reliability of the judgment results.