The effects of extreme hemodilutions on the autoregulation of cerebral blood flow, electroencephalogram and cerebral metabolic rate of oxygen in the dog

Abstract

The effects of profound (hematocrit value, Ht 20%) and extreme (Ht 5%)hemodilutions on the relationship bet ween the mean arterial pressure (MAP) and the cerebral blood flow (CBF) were studied in pentobarbital-anesthetized dogs. A regression line was found between the CBF and Ht values during normotensivehemodilution (MAP100torr): CBF(ml/100gmin) = −98.9 log Ht (%) + 195.5 (p< 0.001). The CBF was increased by hemodilution, but the range of its autoregulation was narrowed, suggesting a progressive susceptibility of CBF to blood pressure with hemodilution. The electroencephalogram (EEG) was not significantly changed by hemodilution within the range of the CBF autoregulation, below which it became slowed. In contrast, the cerebral metabolic rate of oxygen (CMRO2,) was decreased by hemodilution even within the range of the CBF autoregulation, while there were no significant differences in CMRO2values between MAPs of 100 and 40 torr. Thus, the brain function in terms of the EEG seemed to correlate more with the autoregulatory mechanism of the CBF than with theCMRO2, value in the hemodiluted states. © 1985 American Heart Association, Inc.