The Limitation of Bloodless Surgery and Development of Fluid Therapy 邓硕曾 教授 Shuozeng Deng, MD 武汉亚洲心脏病医院麻醉科 武汉 430022 Department of Anesthesiology,Wuhan Asia Heart Hospital Wuhan 430022 ABSTRACT This review illustrated the compensatory mechanism and limitation of acute normovalemic anemia.Therefore,the blood transfusion trigger is an essential target value for bloodless surgery.The appropriate threshold of Hb may be 70g/L for most surgical patient,but the transfusion trigger of Hb for aged and high risk patients should be increased to 100g/L.The affected factors of hemodilution may result from advanced age, anesthetics, controlled hypotension, pulmonary dysfunction and critically ill patients. Arguments over the best choice of fluid (colloid vs crystalloid)for volume resuscitation have been debated for more than 30 years. Recent studies have focused on the differences between administering saline vs "balanced"electrolyte solutions. It was found that the perioperative use of balanced solutions was associated with lower incidence of hyperchloremic acidosis compared with 0.9% saline. Moreover,the quality of recovery may be superior when colloid/crystalloid combination was used compared with crystalloid alone in patient undergoing major surgery. It was demonstrated that"goal directed fluid administration",using fluid and inotropes to achieve the targeting specific values for Cl, DO2 and VO2, resulted in a reduction in mortality and morbidity and an outcome benefit for patients. It can be used as a measurement for fluid therapy. 手术避免同种输血一直是我们的理想,但“理想”的无血手术中心,围术期输血率仍占16%,无血手术仍有一定限度。因为无血手术的前提是维持组织足够氧供(DO2),满足代谢的需要[1]。 一、急性等容性贫血(acute normovolemic anemia) 急性等容贫血与急性等容血液稀释(ANH)有密切的关系,它取决于增加心排血量(CO),和氧的提取(EO2),而增加EO2有赖于微循环的活化,使组织提取更多的O2,降低静脉氧饱和度(SvO2)[2]。SvO2是DO2的间接指标。急性等容贫血的代偿见图1。 但急性等容贫血有一定限度,当Hb<60g/L,Hct<18%时就会失代偿,使DO2下降并发生细胞低氧。急性贫血同时会导致心肌收缩力下降使CO降低,还会造成凝血紊乱和低凝状态,增加出血和渗血。CO下降和凝血紊乱又会使DO2进一步下降。尽管我们可以靠增加血容量,提高吸入O2浓度(Fi O2)或应用血液代用品补充O2的载体,但提高Fi O2会增加肺内O2自由基造成组织损伤,而血液代用品尚处于试验阶段。 二、影响急性等容血液稀释的因素 影响急性等容血液稀释耐受的主要因素是:1)年龄,老年人对CaO2下降的代偿受限,因此不能耐受大容量的血液稀释;2)麻醉药,麻醉药会减弱CO对等容血液稀释的反应,使CO的增加受限;3)控制性降压,使用血管扩张药会干扰正常血流再分布,损害肾和内脏氧合;4)呼吸功能不全,血液稀释使低氧性肺血管收缩(HPV)的代偿下降,损害肺的气体交换,降低血液携氧能力;5)危重病人,因心功能不全或低O2血症使氧提取减少,又可因发热、疼痛、应激、呼吸作功增加使组织氧需增加。 尤其是冠心病人,因心肌O2提取减少,血液稀释后冠脉储备降低,如果术前应用了β阻滞药或抗心律失常药后,CO下降,因而需要较高的Hct(>30%),才能保证心肌氧供需平衡。 |