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姚尚龙
华中科技大学同济医学院附属协和医院麻醉学教研室(430022)
分娩镇痛在诸多的方法中,椎管内阻滞仍然是最有效的方法[1,2]。理想的局麻药应该是产生可靠的感觉阻滞,无运动阻滞,毒性反应低。布比卡因是一种长效的局麻药,在产科镇痛中如果过量还会产生心脏毒性和神经后遗症。1979年Albright[3] 报告了产妇意外地接受布比卡因血管内注射,引起了心血管衰竭而致命,故美国FDA 禁止产妇硬膜外使用 0.75% 布比卡因。由于布比卡因的急性致命性的心血管毒性,因此迫切需要研制适合产科病人应用的新型长效局麻药。
4.局麻药与阿片类药联合用于分娩镇痛
4.长效局麻药分娩镇痛中的不良反应
4.1低血压 分娩镇痛采用硬膜外、蛛网膜下腔阻滞或硬膜外-蛛网膜下腔联合麻醉时,如收缩压降至<90mmHg,或比基础值降低20%~30%,称为低血压。其发生机制是下胸腰段脊神经阻滞后,腹肌松弛,妊娠子宫压迫下腔静脉导致静脉回流障碍,心排出量突然减少;此外,交感神经阻滞后外周血管扩张也是引起血压下降的原因之一。如低血压时间过长,可能导致胎盘血流灌注减少,胎儿低氧血症和酸血症,重者危及新生儿存活。因此,应密切监测血压、心率、呼吸及产妇其他变化,同时行胎儿心率监测,开放静脉输液,避免阻滞平面过广,及时变换产妇体位。当出现低血压时,将产妇置于左侧卧位,必要时静脉注射麻黄碱5~10mg。
4.2局麻药中毒 多发生在区域阻滞过程中,尤其是骶管阻滞者。其主要原因是局麻药误注入血管或因局麻药用量大,经局部血管吸收迅速引起。
4.3对子宫收缩和产程的影响 由于用药种类、药物浓度以及用药时间的不同,椎管内分娩镇痛对宫缩的影响各不相同。一般局麻药浓度越低、用药时间恰当,镇痛过程中辅以一定量的催产素,均可以减轻宫缩抑制作用。
4.4对胎心的影响 分娩镇痛时,可以出现胎心率加快或减慢。引起胎心率改变的可能因素很多,芬太尼等麻醉性镇痛药对心率的抑制作用是一个因素,芬太尼引起子宫收缩过度活跃影响胎盘血循环又是另一个因素。但是,大多数研究者认为硬膜外分娩镇痛不会引起胎心减慢[19]。一旦出现任何不能改善的胎盘血流下降、胎儿心率改变,应当机立断,终止自然分娩,以确保母婴安全。
总之,随着分娩镇痛技术日臻完善,药物不断改进,产科分娩镇痛的安全性和有效性将大大提高,分娩镇痛具有良好的发展前景。
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