Cook D J, Anderson R E, Michenfelder J D, Oliver W C, Orszulak T A, Daly R C, Bryce R D
Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota 55905.
Ann Thorac Surg. 1995 Mar;59(3):614-20. doi: 10.1016/0003-4975(94)00956-2.
This study simultaneously compared the standard Kety-Schmidt and the modified xenon-133 (133Xe) clearance techniques for measuring cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRO2) during cardiac operations. The validity of the CBF method is important because our management of the patient during cardiopulmonary bypass (CPB) is based, in part, on our understanding of the cerebral hemodynamics during CPB. In 20 patients undergoing coronary artery bypass grafting, CBF and CMRO2 were determined by both methods. Measurements were made before onset of CPB and once during CPB. Ten patients underwent CPB with systemic normothermia (37 degrees C) and 10 with systemic hypothermia (27 degrees C). Anesthesia consisted of fentanyl and midazolam. CPB pump flows were kept at 2.2 to 2.4 L.min-1.m-2 and alpha-stat pH management was used. Xenon-133 clearance significantly underestimated CBF and CMRO2 relative to the Kety-Schmidt technique before CPB and at both bypass temperatures. Values obtained by 133Xe clearance were approximately 50% of that measured by the Kety-Schmidt method. The modified 133Xe technique as typically used during cardiac operations does not appear to measure CBF accurately; this leads to corresponding errors in CMRO2 calculations. Determination of CMRO2 and cerebral autoregulatory function during cardiac operations appears to be more appropriate if based on the more direct Kety-Schmidt technique. Accordingly, our management of CPB with respect to cerebral perfusion as it has been determined by the modified 133Xe clearance method may require reassessment.
本研究同时比较了标准的凯蒂-施密特（Kety-Schmidt）技术和改良的氙-133（¹³³Xe）清除技术，用于在心脏手术期间测量脑血流量（CBF）和脑氧代谢率（CMRO₂）。CBF测量方法的有效性很重要，因为我们在体外循环（CPB）期间对患者的管理部分基于我们对CPB期间脑血流动力学的理解。在20例接受冠状动脉旁路移植术的患者中，通过两种方法测定了CBF和CMRO₂。在CPB开始前和CPB期间进行了一次测量。10例患者在全身正常体温（37摄氏度）下进行CPB，10例在全身低温（27摄氏度）下进行CPB。麻醉采用芬太尼和咪达唑仑。CPB泵流量保持在2.2至2.4L·min⁻¹·m⁻²，并采用α稳态pH管理。相对于CPB前和两种旁路温度下的凯蒂-施密特技术，氙-133清除率显著低估了CBF和CMRO₂。通过¹³³Xe清除率获得的值约为凯蒂-施密特方法测量值的50%。心脏手术中通常使用的改良¹³³Xe技术似乎不能准确测量CBF；这导致CMRO₂计算中出现相应误差。如果基于更直接的凯蒂-施密特技术，在心脏手术期间测定CMRO₂和脑自动调节功能似乎更合适。因此，我们基于改良的¹³³Xe清除方法确定的关于脑灌注的CPB管理可能需要重新评估。
