Schwender D, Daunderer M, Klasing S, Conzen P, Finsterer U, Peter K
Institut für Anästhesiologie, Ludwig-Maximilians-Universität München.
Anaesthesist. 1996 Feb;45 Suppl 1:S46-51.
Midlatency auditory evoked potentials (MLAEP) are suppressed dose-dependently during anaesthesia with a variety of general anaesthetics. Therefore, MLAEP have been proposed to measure depth of anaesthesia and to indicate intraoperative awareness. Several studies give evidence of a close relationship between MLAEP and motor signs of wakefulness, intraoperative awareness, and explicit and implicit memory functions during general anaesthesia. Summarising these data, one may conclude that there is a close hierarchical relation between cognitive function, memory and wakefulness during anaesthesia, and MLAEP latencies. A short Nb latency below 45 ms is consistent with conscious awareness and unimpaired memory function with explicit recall and adequate response to commands. When Nb latency increases to 45-50 ms, it may be associated with conscious awareness. Patients still respond to commands, but memory formation is impaired and explicit recall is lost. A further increase of Nb latencies seems to be consistent with unconscious awareness, characterised by implicit memory of intraoperative events; 60 ms seems to be the threshold value for motor signs of wakefulness during anaesthesia. With a further increase of MLAEP latency during anaesthesia, conscious awareness and memory formation, explicit and implicit recall, response to commands, and spontaneous purposeful movements during anaesthesia are blocked. The new volatile anaesthetic sevoflurane leads to a dose-dependent increase in MLAEP peak latencies and a decrease in MLAEP amplitudes. At about 1.5 vol.% end-expiratory sevoflurane concentration, MLAEP are significantly suppressed and Nb latency is in the range of 68-80 ms. Therefore, from the present data and those from the literature, one may expect that sevoflurane at concentrations greater than 1.5 vol.% for general anaesthesia would be able to suppress awareness phenomena such as purposeful movements, auditory perception, intraoperative wakefulness and awareness, memory formation, and explicit and implicit recall of intraoperative events.
在使用多种全身麻醉药进行麻醉期间，中潜伏期听觉诱发电位（MLAEP）会出现剂量依赖性抑制。因此，有人提出MLAEP可用于测量麻醉深度并提示术中知晓情况。多项研究证明，在全身麻醉期间，MLAEP与清醒的运动体征、术中知晓以及显性和隐性记忆功能之间存在密切关系。总结这些数据可以得出结论，麻醉期间认知功能、记忆和清醒状态与MLAEP潜伏期之间存在密切的层级关系。低于45毫秒的短Nb潜伏期与清醒意识、未受损的记忆功能、显性回忆以及对指令的充分反应相一致。当Nb潜伏期增加到45 - 50毫秒时，可能与清醒意识有关。患者仍能对指令做出反应，但记忆形成受损且显性回忆丧失。Nb潜伏期的进一步增加似乎与无意识状态相符，其特征为对术中事件的隐性记忆；60毫秒似乎是麻醉期间清醒运动体征的阈值。随着麻醉期间MLAEP潜伏期的进一步增加，清醒意识和记忆形成、显性和隐性回忆、对指令的反应以及麻醉期间的自发有目的运动均被阻断。新型挥发性麻醉药七氟醚会导致MLAEP峰潜伏期剂量依赖性增加以及MLAEP波幅降低。在呼气末七氟醚浓度约为1.5%体积分数时，MLAEP被显著抑制，且Nb潜伏期在68 - 80毫秒范围内。因此，根据目前的数据以及文献中的数据，可以预期，用于全身麻醉的七氟醚浓度大于1.5%体积分数时，将能够抑制诸如目的性运动、听觉感知、术中清醒和知晓、记忆形成以及对术中事件的显性和隐性回忆等知晓现象。
