Cook D J, Oliver W C, Orszulak T A, Daly R C, Bryce R D
Department of Anesthesiology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
Ann Thorac Surg. 1995 Dec;60(6):1671-7. doi: 10.1016/0003-4975(95)00648-6.
The neurologic effects of warm heart operations is a subject of popular interest. The purpose of this study was to examine the adequacy of cerebral oxygenation during normothermic cardiopulmonary bypass and better define the relationship between hematocrit, temperature, and brain oxygen delivery.
Cerebral blood flow, metabolic rate, and oxygen delivery were measured in 60 patients randomized to normothermic (37 degrees C) or hypothermic (27 degrees C) cardiopulmonary bypass. The nitrous oxide saturation technique of Kety and Schmidt was used for cerebral blood flow determinations. Both temperature groups underwent moderate (31%) hemodilution.
During normothermic cardiopulmonary bypass, cerebral blood flow increased secondary to hemodilution and decreased cerebral vascular resistance; a normal matching of oxygen demand and delivery was maintained. During hypothermic bypass, hemodilution and hypothermia had essentially equal, opposing effects on cerebral vascular resistance and blood flow. With hypothermia, brain oxygen demand and delivery were both reduced but not closely coupled.
From the standpoint of global cerebral perfusion and oxygenation, our data support the practice of "warm" heart operations. It clarifies the marked influence of hematocrit on cerebral blood flow and delineates the interaction of temperature and hematocrit on cerebral oxygen delivery. It also suggests that additional investigation to better define "temperature-appropriate" hemodilution during cardiopulmonary bypass is indicated.
心脏温血手术的神经学效应是一个备受关注的课题。本研究的目的是检测常温体外循环期间脑氧合是否充足，并更好地明确血细胞比容、温度与脑氧输送之间的关系。
对60例随机接受常温（37℃）或低温（27℃）体外循环的患者测量脑血流量、代谢率和氧输送。采用凯蒂和施密特的氧化亚氮饱和技术测定脑血流量。两个温度组均进行了中度（31%）血液稀释。
在常温体外循环期间，脑血流量因血液稀释而增加，脑血管阻力降低；氧需求与输送保持正常匹配。在低温体外循环期间，血液稀释和低温对脑血管阻力和血流量的影响基本相等但方向相反。低温时，脑氧需求和输送均降低，但未紧密耦合。
从整体脑灌注和氧合的角度来看，我们的数据支持“温血”心脏手术的做法。它阐明了血细胞比容对脑血流量的显著影响，并描述了温度和血细胞比容对脑氧输送的相互作用。它还表明，需要进行更多研究以更好地明确体外循环期间“适合温度”的血液稀释。
