Mezrow C K, Sadeghi A M, Gandsas A, Dapunt O E, Shiang H H, Zappulla R A, Griepp R B
Department of Cardiothoracic Surgery, Mount Sinai Medical Center, New York, New York 10029.
Ann Thorac Surg. 1994 Mar;57(3):532-9; discussion 539. doi: 10.1016/0003-4975(94)90541-x.
Although both hypothermic circulatory arrest (HCA) and low-flow cardiopulmonary bypass (CPB) are accepted techniques for the operative management of complex cardiovascular pathology, the potential for neurologic sequelae is still a concern. To assess the relative safety of these techniques, we compared cerebral hemodynamics and clinical outcome in two groups of puppies. Sixteen puppies underwent 45 minutes of either HCA or low-flow CPB (25 mL.kg-1.min-1) after cooling to 13 degrees C. Methodology included radioactive microsphere determination of cerebral blood flow; calculation of cerebral oxygen extraction (arteriovenous oxygen content difference) and consumption; measurement of glucose consumption, and determination of cerebrovascular resistance. Measurements were obtained at baseline (37 degrees C), 13 degrees C, and 30 degrees C and at 2, 4, and 8 hours after HCA or low-flow CPB. No neurologic deficits were observed in any of the survivors (15/16). In both groups, cerebral metabolic rate of oxygen was maintained at baseline or greater levels postoperatively. Cerebrovascular resistance rose slightly in the low-flow CPB group postoperatively in contrast to a marked elevation in the HCA group. During the period of high cerebrovascular resistance after HCA, cerebral metabolic rate of oxygen was maintained by increased oxygen extraction. After low-flow CPB, oxygen extraction was not significantly different from baseline, presumably because of less severe changes in cerebrovascular resistance. Glucose metabolism followed the same trends as oxygen metabolism in both groups. These data suggest that after HCA there is a vulnerable interval, lasting as late as 8 hours postoperatively, in which cerebrovascular resistance remains high and cerebral metabolism is maintained primarily by high oxygen and glucose extraction. Any additional stress during this interval (a decrease in arterial oxygen content or perfusion pressure) could result in cerebral injury.
尽管低温循环停搏（HCA）和低流量体外循环（CPB）都是用于复杂心血管疾病手术管理的公认技术，但神经后遗症的可能性仍然是一个令人担忧的问题。为了评估这些技术的相对安全性，我们比较了两组幼犬的脑血流动力学和临床结果。16只幼犬在冷却至13摄氏度后接受了45分钟的HCA或低流量CPB（25 mL·kg-1·min-1）。方法包括用放射性微球测定脑血流量；计算脑氧摄取（动静脉氧含量差）和消耗量；测量葡萄糖消耗量，并测定脑血管阻力。在基线（37摄氏度）、13摄氏度和30摄氏度以及HCA或低流量CPB后2、4和8小时进行测量。所有存活者（15/16）均未观察到神经功能缺损。在两组中，术后脑氧代谢率均维持在基线水平或更高水平。与HCA组显著升高相比，低流量CPB组术后脑血管阻力略有上升。在HCA后脑血管阻力较高的时期，脑氧代谢率通过增加氧摄取得以维持。低流量CPB后，氧摄取与基线无显著差异，可能是因为脑血管阻力变化较轻。两组中葡萄糖代谢与氧代谢趋势相同。这些数据表明，HCA后存在一个脆弱期，持续至术后8小时，在此期间脑血管阻力仍然很高，脑代谢主要通过高氧和葡萄糖摄取来维持。在此期间的任何额外应激（动脉氧含量或灌注压降低）都可能导致脑损伤。
