Robins Kay, Lyons Gordon
Department of Anaesthesia, York Hospital, York, UK.
Anesth Analg. 2009 Sep;109(3):886-90. doi: 10.1213/ane.0b013e3181af83c1.
Intraoperative awareness is defined as the spontaneous recall of an event occurring during general anesthesia. A move away from rigid anesthetic protocols, which were designed to limit drug transmission across the placenta, has reduced the incidence of awareness during cesarean delivery to approximately 0.26%. Nevertheless, it remains an undesirable complication with potential for the development of posttraumatic stress disorder. Assessing depth of anesthesia remains a challenge for the anesthesia provider as clinical signs are unreliable and there is no sensitive and specific monitor. Bispectral Index monitoring with the goal of scores <60 has been recommended to prevent awareness. Induction drugs vary in their ability to produce amnesia and the period of hypnotic effect is affected by the rate at which they are redistributed. After initiation of anesthesia, volatile anesthetics should be administered to a target of 0.7 minimum alveolar anesthetic concentration, which has been shown to consistently achieve mean Bispectral Index scores <60. Because of its rapid uptake, nitrous oxide remains an important adjunct to reduce the risk of awareness during emergency cesarean delivery. In the absence of fetal compromise, there is no rationale for an inspired oxygen concentration above 0.33. Deeper levels of anesthesia reduce the incidence of awareness; current evidence does not suggest an increased risk of tocolysis or fetal morbidity.
术中知晓被定义为对全身麻醉期间发生事件的自发回忆。过去旨在限制药物透过胎盘传递的严格麻醉方案有所改变，这已将剖宫产术中知晓的发生率降至约0.26%。然而，它仍是一种不良并发症，有可能引发创伤后应激障碍。对麻醉医生来说，评估麻醉深度仍是一项挑战，因为临床体征不可靠，且没有敏感且特异的监测手段。建议采用脑电双频指数监测，目标是使分数<60，以预防术中知晓。诱导药物产生遗忘的能力各不相同，催眠效果的持续时间受其再分布速度的影响。麻醉开始后，挥发性麻醉药应给予至最低肺泡有效浓度为0.7的目标值，这已被证明能持续使脑电双频指数平均分数<60。由于氧化亚氮摄取迅速，它仍是紧急剖宫产术中降低术中知晓风险的重要辅助药物。在不存在胎儿窘迫的情况下，没有理由将吸入氧浓度设定在0.33以上。更深的麻醉水平可降低术中知晓的发生率；目前的证据并未表明有增加宫缩抑制或胎儿发病的风险。
