兔深低温停循环高氧管理脑保护的实验研究

【作者】 王茜；

【导师】 龙村；

【作者基本信息】 北京协和医学院 ， 麻醉学， 2012， 博士

【摘要】 研究背景心血管外科一些急、危、重、复杂的手术常需在深低温停循环(deep hypothermic circulatory arrest, DHCA)下完成,但其重要脏器(尤其中枢神经系统)并发症及死亡率在总体心血管外科死亡及其它不良预后病例中占很大比例。因此,提高此类患者的疗效,将对心血管外科总体预后的改善做出巨大贡献。深低温停循环技术为复杂心脏病手术提供了安静无血的环境,同时也对包括颅脑在内的全身脏器提供低温保护,这项里程碑式的技术临床应用后,婴幼儿复杂性先天性心脏病、累及主动脉弓部的疾病如Stanford A型主动脉夹层等复杂心血管疾病的手术治疗得以安全顺利的进行和发展。但同时DHCA技术对机体影响较大,术后神经精神并发症较多。为改善疗效,经双侧颈总动脉顺行或经上腔静脉逆行脑灌注等脑保护方法曾相继被探索和应用,但前者操作复杂,后者不符合生理。经右腋动脉顺行选择性脑灌注(antegrade selective cerebral perfusion, ASCP)操作简单、符合生理,有效地降低了患者神经系统并发症的发生率,近年来,已发展成为深低温停循环中最经典的脑保护措施。虽然ASCP脑保护效果确切,但近期的研究指出在涉及主动脉弓部的手术中,院内死亡率有6-23%,永久性神经系统功能障碍发生率为2-6%,暂时性神经系统功能障碍发生率为5.6-37.9%,问题仍然不容忽视。研究者们一致认为单一方法难以在此类复杂病例中取得完美的脑保护效果,尤其在DebakeyⅢ型主动脉夹层侧开胸行降主动脉替换以及肺动脉血栓内膜剥脱术等丕能经右腋动脉插管进行ASCP的患者,仍然面临完全DHCA的局面。此外,少数Willis环不完整和／或脑血管病变的患者还可能被暴露于单侧脑灌注的潜在危险中。因此寻找新的,特别是在完全DHCA期间仍然能够提供脑保护的方法刻不容缓。为此,很多学者进行了大量的研究,在众多方面都取得了进展。体外循环中的给氧策略和血气管理也是其中的一个研究热点。正常人动脉血氧分压约为70-100mmHg,在体外循环中采用不同的给氧策略和血气管理方式,会使动脉血氧分压(arterial oxygen pressure,PaO2)有较大的波动(100-700mmHg)。在ASCP+DHCA时采用何种血气管理方法最为恰当目前尚未有定论。有研究表明,在常温或浅低温时PaO2过高可能引起脑血管痉挛、骨骼肌微循环障碍和肺损伤,加剧氧化应激造成器官组织氧中毒等不良反应[4]；但后来却有研究发现深低温时高氧会产生不同效果。Dexter等[5]研究发现,随着温度的降低,氧与血红蛋白不断增加的亲和力导致进行性氧解离障碍,这种解离障碍在27℃还很微弱,但到了17℃则变得很大。所以在深低温时脑组织主要利用溶解氧,而非血红蛋白携氧[6l。常规体外循环的血气管理有可能并不足以提供充足的溶解氧,而在深低温停循环期间一旦脑供氧不足,很容易造成脑缺氧,继而产生并发症。Nollert等[7]的研究也得到了类似的结果。根据这些研究基础,阜外医院的杨九光等提出了“深低温期间高氧血气管理”(简称“高氧管理”)的具体方法：即指在深低温停循环或深低温低、微流量手术中,常温、浅、中低温体外循环期间注意避免高氧(维持Pa02在100-200mmHg)；而在深低温时提高FiO2至60-100%,使Pa02达到300-700mmHg,从而提高深低温期间溶解氧的供给,增加脑氧储备,并在复温早期迅速有效地偿还氧债,减少/避免脑及其它器官缺氧并发症发生以达到保护效果的方法。“深低温期间高氧管理”操作简便,而且不增加患者治疗费用和外科医师的操作,其脑保护效如被成功验证而得以在临床推广,则有可能降患者低神经系统并发症的发生率,对心血管外科总体预后的改善做出贡献。目的众多脑保护措施应用于涉及主动脉弓部、婴幼儿复杂性先天性心脏病及其它复杂心脏手术中,以期降低接受这些复杂手术患者术后的死亡率和神经系统并发症的发生率,期望患者获得较好的预后。顺行选择性脑灌注联合深低温停循环是目前在涉及主动脉弓部及其它复杂心脏手术中应用最为广泛的一种脑保护方法。对涉及深低温的体外循环给氧策略仍有争议。本实验旨在通过对深低温期间高氧血气管理对深低温停循环兔血气指标、脑氧饱和度、脑组织生化指标、脑损伤标志物、脑组织形态学及脑组织含水量等的研究,探讨深低温期间高氧管理的脑保护作用,为深低温期间高氧管理在临床的应用提供实验经验和实验基础。方法建立兔深低温停循环(DHCA)+顺行选择性脑灌注(ASCP)动物模型,将32只11-13周龄雄性新西兰兔(体重2.6-3.4kg)用随机数字表法随机分为4组：DHCA组(D组),ASCP组(S组),DHCA十高氧管理组(DH组),ASCP+高氧管理组(SH组),每组8只。术中取血标本检测动脉血氧分压(Pa02)、动脉血氧饱和度(arterial oxygen saturation, SaO2)、颈静脉球血氧分压(jugular venous oxygen pressure, PjvO2)、颈静脉球血氧饱和度(jugular venous oxygen saturation, SjvO2)和血乳酸含量(lactic acid, Lac),连续监测兔脑氧饱和度值；术后检测脑组织超氧化物歧化酶(superoxide dismutase, SOD)活性、丙二醛(malondialdehyde,MDA)含量、糖原含量,乳酸含量,血中神经元特异性烯醇化酶和s100B蛋白含量及脑组织含水量；脑组织标本使用光镜电镜进行形态学检查。结果停循环前SH组和DH组的PaO2、PjvO2、SjvO2均高于其它两组,与停循环相关的复灌前和恢复灌注5分钟两个时点,SH组的PaO2、PjvO2和SjvO2均高于其余三组,差异具有统计学意义(p<0.05)。SH组在整个停循环过程中与其余三组相比有较高的脑氧饱和度值,差异具有统计学意义(p<0.05)。SH组有较高的脑组织超氧化物歧化酶活性,较低的MDA含量和乳酸含量,SH组有较低的s100B蛋白和神经元特异性烯醇化酶水平,SH组有较低的脑组织含水量。与其余三组相比,光镜及透射电镜观察到SH组保持了更好的神经细胞包括细胞膜、细胞器和细胞核的形态。结论深低温期间的高氧血气管理相比常氧管理能提供更良好的氧供,在深低温停循环联合顺行选择性脑灌注中使用高氧血气管理能够减低可能的脑损伤,并能够在复温阶段快速地偿还氧债,保持脑组织较好的氧供需平衡关系,具有脑保护作用。更多还原

【Abstract】 ObjectivesVarious brain protective techniques were used to decrease the mortality and the incidence of neurological complications during aortic arch surgery, complex neonatal congenital heart surgery and the other complex cardiovascular sugery, in order to achieve good clinical outcome. Combination of ASCP and DHCA was suggested as the most popularly used method of cerebral protection during the aortic arch surgery and the other complex cardiovascular sugery. However, the oxygen management for this combination strategy is still controversial. The aim of this study was to investigate the effects of hyperoxia management during deep hypothermia in circulatroy arrest rabbit on the blood gas indexes, regional cerebral oxygen saturation, biochemical indexes, cerebral injury markers, morphology of brain tissue and the ratio of water to brain, to determine the cerebral protective effects of hyperoxia management, to get the experimental experience and basics for clinical application of hyperoxia management.MethodsA deep hypothermic circulatory arrest (DHCA) and antegrade selective cerebral perfusion (ASCP) rabbit model was established. Thirty-two11-13week-old male New Zealand rabbits (weighing2.6to3.4kg) were assigned to four groups with a random number table:a deep hypothermic circulatory arrest group (D group), an antegrade selective cerebral perfusion group (S group), a DHCA+hyperoxia management group (DH group) and an ASCP+hyperoxia management group (SH group). There were eight rabbits in each group. We recorded the intraoperative values of arterial oxygen pressure (PaO2), arterial oxygen saturation (SaO2), jugular venous oxygen pressure (PjvO2), jugular venous oxygen saturation (SjvO2), blood lactate level and continous regional cerebral tissue oxygen saturation (rSO2). The levels of neuron-specific enolase (NSE) and s100B proteins of the blood, the brain superoxide dismutase activity, malondialdehyde levels, lactic acid levels, glycogen levels and ratio of water to brain were measured after the operation. Light microscope and electron microscope were used for morphological examination of brain tissue specimens.ResultsBefore initiating circulatory arrest, levels of PaO2, PjvO2, and SjvO2in the SH group and DH group were significantly higher than those of the D and S groups. Before initiating reperfusion and five minutes after reperfusion (the time points related to circulatory arrest), levels of PaO2, PjvO2, and SjvO2in the SH group were significantly higher than those of the other three groups (p<0.05). In the duration of CA, rSO2in the SH group was significantly higher than that in the other three groups (p<0.05). The brain tissue of the animal in the SH group was with higher SOD activity, lower MDA level and lower lactic acid level than in the other group. There were lower s100B level and NSE level in the SH group than those in the other groups. Compared with the other three groups, the brain tissue of the animal in the SH group kept a better cell morphology of neuron including cell membrane, cellular organelle, cell nucleus.ConclusionsHyperoxia management during deep hypothermia provided substantial dissolved oxygen and better oxygen supply over normoxia management. Hyperoxia management for the combination of ASCP and DHCA could reduce the risk of cerebral injury, repay the oxygen debt quickly during the rewarming period, keep a good oxygen supply and demand balance. This study confirms that hyperoxia management for the combination of ASCP and DHCA provides a better cerebral protection over normoxia management in a rabbit model.更多还原