Scheufler Kai-Michael, Zentner Josef
Department of Neurosurgery, University of Freiburg, Freiburg, Germany.
Anesth Analg. 2002 Apr;94(4):907-12, table of contents. doi: 10.1097/00000539-200204000-00025.
We characterized the effects of various stimulation patterns on motor-evoked potentials (MEPs) elicited by repetitive transcranial magnetoelectric stimulation at different levels of cortical suppression by propofol. In 20 patients undergoing lumbar disk surgery, propofol target plasma concentrations (PTPCs) were increased incrementally by target plasma-level controlled infusion during the induction of anesthesia. MEPs were recorded from the muscles of the upper extremities after single, double, and quadruple magnetoelectric stimulation at 500, 200, and 100 Hz. The mean PTPC during loss of responsiveness to verbal instructions (CP50) was 3 microg/mL (CP(95), 5 microg/mL). At PTPCs <3 microg/mL, maximal MEP amplitudes were elicited by quadruple stimulation at 100 Hz. At PTPCs > or =3 microg/mL, four pulses at 200 Hz yielded peak MEP amplitudes. Therefore, quadruple magnetoelectric stimulation at 100 Hz yields peak myogenic responses in awake patients. With progressive cortical suppression resulting from PTPCs beyond 3 microg/mL, the most effective stimulation frequency shifts to 200 Hz. This may be explained by a differential dose-dependent action of propofol on GABAergic cortical interneurons, corresponding to the clinically observed state of vigilance. Recording of spinal cord evoked potentials will aid in further elucidation of the modulatory effects of general anesthesia on intracortical facilitation.
We investigated the effect of different transcranial magnetoelectric stimulation paradigms on motor-evoked potentials during different levels of cortical suppression by propofol. The most effective stimulation frequency seems to change from 100 to 200 Hz during progressive propofol dose escalation, possibly because of specific interaction with cortical interneurons.
我们研究了在丙泊酚诱导不同程度皮质抑制时，各种刺激模式对重复经颅磁电刺激诱发的运动诱发电位（MEP）的影响。在20例行腰椎间盘手术的患者中，麻醉诱导期间通过靶血浆浓度控制输注逐渐增加丙泊酚靶血浆浓度（PTPC）。在500、200和100Hz频率下进行单次、双次和四次磁电刺激后，记录上肢肌肉的MEP。对言语指令失去反应时的平均PTPC（CP50）为3μg/mL（CP95为5μg/mL）。在PTPC<3μg/mL时，100Hz的四次刺激可诱发最大MEP波幅。在PTPC≥3μg/mL时，200Hz的四个脉冲可产生峰值MEP波幅。因此，100Hz的四次磁电刺激在清醒患者中可产生峰值肌源性反应。随着PTPC超过3μg/mL导致皮质抑制逐渐加重，最有效的刺激频率转变为200Hz。这可能是由于丙泊酚对GABA能皮质中间神经元的剂量依赖性差异作用，这与临床观察到的警觉状态相对应。记录脊髓诱发电位将有助于进一步阐明全身麻醉对皮质内易化的调节作用。
我们研究了不同经颅磁电刺激模式在丙泊酚诱导不同程度皮质抑制时对运动诱发电位（MEP）产生影响。在丙泊酚剂量逐渐增加的过程中，最有效的刺激频率似乎从100Hz变为200Hz，这可能是由于与皮质中间神经元的特定相互作用所致。
