Liam B L, Plöchl W, Cook D J, Orszulak T A, Daly R C
Department of Anesthesiology, Mayo Clinic, Rochester, Minn 55905, USA.
J Thorac Cardiovasc Surg. 1998 May;115(5):1203-8. doi: 10.1016/S0022-5223(98)70422-2.
The purpose of this study was to determine the minimum hematocrit value that can support whole body oxygen consumption during normothermic cardiopulmonary bypass. The effect of hemodilution on peripheral resistance, whole body oxygen delivery, and oxygen consumption was determined over a range of hematocrit values.
Measurements were obtained during 38 degrees C cardiopulmonary bypass with progressive normovolemic hemodilution (hematocrit value 40% to 9%) in nine dogs. Dextran 70 (6%) was used as a diluent. Anesthesia consisted of high-dose fentanyl and midazolam. A mean arterial pressure of 60 mm Hg was maintained throughout cardiopulmonary bypass via increases in pump flow.
Progressive hemodilution was associated with a decreasing total peripheral resistance. During normothermic cardiopulmonary bypass with a whole blood prime, the whole body oxygen consumption approximated values previously reported in dogs under nonbypass conditions. Oxygen delivery and whole body oxygen uptake were maintained between a hematocrit value of 39% and 25%. Significant decreases for both were seen when the hematocrit value was reduced to 18% and below.
A hematocrit level greater than 18% was needed to maintain systemic oxygen delivery and consumption during warm cardiopulmonary bypass. The critical hematocrit value may be higher under bypass than nonbypass conditions because the flow increases that are practical during cardiopulmonary bypass do not approximate those seen in response to hemodilution of the intact circulation. Finally, the critical hematocrit value for the body may be higher than that required for the brain during warm cardiopulmonary bypass.
本研究旨在确定在常温体外循环期间能够维持全身氧耗的最低血细胞比容值。在一系列血细胞比容值范围内，测定血液稀释对外周阻力、全身氧输送和氧耗的影响。
在9只犬进行38℃体外循环并逐步进行正常血容量血液稀释（血细胞比容值从40%至9%）的过程中进行测量。使用6%的右旋糖酐70作为稀释剂。麻醉采用高剂量芬太尼和咪达唑仑。在整个体外循环过程中，通过增加泵流量维持平均动脉压60 mmHg。
逐步血液稀释与总外周阻力降低相关。在以全血预充的常温体外循环期间，全身氧耗接近先前报道的犬在非体外循环条件下的值。在血细胞比容值为39%至25%之间，氧输送和全身氧摄取得以维持。当血细胞比容值降至18%及以下时，两者均显著下降。
在温体外循环期间，需要血细胞比容水平高于18%才能维持全身氧输送和氧耗。由于体外循环期间实际的流量增加与完整循环血液稀释时的流量增加不同，因此体外循环下的临界血细胞比容值可能高于非体外循环条件下的。最后，在温体外循环期间，身体的临界血细胞比容值可能高于大脑所需的值。
