Department of Anaesthesiology, Helios Clinic Wuppertal, Witten/Herdecke University, 42283 Wuppertal, Germany.
Department of Anaesthesiology, Klinikum rechts der Isar, Technische Universität München, München, Germany.
Br J Anaesth. 2014 Jun;112(6):1067-74. doi: 10.1093/bja/aeu016. Epub 2014 Mar 20.
MAC (minimum alveolar concentration of an inhaled anaesthetic) and CP₅₀i (minimum plasma concentration of i.v. anaesthetics) are well-established measures to compare potencies of anaesthetics. The underlying clinical endpoint immobility reflects mainly effects of anaesthetics on the spinal cord, which limits the use of this measure for comparison of effects on the main target organ of general anaesthesia--the brain. The present study determines the median concentration of sevoflurane, isoflurane, and propofol that induce the onset of electroencephalogram (EEG) suppression ('silent second'): MACBS and CP₅₀BS.
Fifty-five unpremedicated patients (ASA physical status of I or II) undergoing elective surgery were randomly assigned to receive general anaesthesia with sevoflurane, isoflurane, or propofol. A two-channel EEG was continuously recorded to identify 'silent second'. Independent cross-over pairs were analysed using the 'Dixon's up-and-down' method, and MACBS/CP₅₀BS values were calculated by logistic regression.
CP₅₀BS was 4.9 µg ml(-1) for propofol. MACBS was 2.9 vol% for sevoflurane and 1.5 vol% for isoflurane. CP₅₀BS of propofol was less than one-third of CP₅₀i, whereas MACBS of sevoflurane was >1.4-fold of MAC; MACBS of isoflurane was 1.3-fold of MAC.
Immobility and cerebral effects reflect different entities of anaesthetic action. The median concentration of anaesthetic drug (volatile or i.v. agent) required to induce 'silent second' might be a more useful metric than the median concentration required to prevent movement in response to a surgical stimulus in order to compare relative potencies of anaesthetic agents on the brain. Advantage of the 'silent second' is an easy identification of this endpoint, while such a deep level is not required for clinical anaesthesia.
MAC（吸入麻醉药的最小肺泡浓度）和 CP₅₀i（静脉麻醉药的最小血浆浓度）是比较麻醉剂效力的成熟指标。作为主要的临床终点的运动不能反映麻醉剂对脊髓的主要作用，这限制了该指标在比较麻醉剂对全身麻醉主要靶器官——大脑的作用方面的应用。本研究确定了诱导脑电图（EEG）抑制（“无声秒”）的七氟醚、异氟醚和丙泊酚的中位数浓度：MACBS 和 CP₅₀BS。
55 例未接受术前用药的择期手术患者（ASA 身体状况 I 或 II 级）被随机分为接受七氟醚、异氟醚或丙泊酚全身麻醉。连续记录双通道 EEG 以识别“无声秒”。使用“Dixon 的上下”方法分析独立交叉对，并通过逻辑回归计算 MACBS/CP₅₀BS 值。
CP₅₀BS 为丙泊酚 4.9 µg ml(-1)。MACBS 为七氟醚 2.9 体积%，异氟醚 1.5 体积%。丙泊酚的 CP₅₀BS 不到 CP₅₀i 的三分之一，而七氟醚的 MACBS 是 MAC 的 1.4 倍以上；异氟醚的 MACBS 是 MAC 的 1.3 倍。
运动不能和大脑效应反映了麻醉作用的不同实体。与为了比较麻醉剂对大脑的相对效力而需要防止手术刺激引起的运动所需的麻醉药物（挥发性或静脉内药物）的中位数浓度相比，诱导“无声秒”所需的麻醉药物中位数浓度可能是一种更有用的指标。“无声秒”的优点是易于识别该终点，而临床麻醉不需要如此深的水平。
