CEREBRAL BLOOD-FLOW AND OXYGEN-CONSUMPTION IN ACUTE BRAIN INJURY WITH ACUTE ANEMIA - AN ALTERNATIVE FOR THE CEREBRAL METABOLIC-RATE OF OXYGEN-CONSUMPTION

Objective: To comparatively evaluate cerebral metabolic rate of oxygen consumption and a modification of it, cerebral consumption of oxygen, in patients with acute brain injury with acute anemia. Design: Prospective, observational study. Setting: Neuroscience intensive care unit (ICU) of a university hospital. Patients: Adults (n = 62) with acute brain trauma, undergoing serial xenon-133 studies of regional cerebral blood flow and global cerebral oxygen metabolism, along with other routine monitoring techniques. Measurements and Main Results: In 173 combined studies of blood flow and oxygen metabolism, in the presence of spontaneous decreases in hemoglobin, cerebral metabolic rate of oxygen consumption and cerebral consumption of oxygen were comparatively evaluated in three groups with different hemoglobin levels. Cerebral metabolic rate of oxygen consumption was calculated as the product of averaged regional cerebral blood flow and arterio-jugular oxygen content difference, while cerebral consumption of oxygen was calculated as the product of averaged regional cerebral blood flow and the arterio-jugular oxyhemoglobin saturation difference, i.e., cerebral extraction of oxygen. Results indicated that a decrease of hemoglobin content is paralleled by a decrease in cerebral metabolic rate of oxygen consumption, even though the level of consciousness (coma score) is essentially unchanged across three hemoglobin groups. On the other hand, cerebral consumption of oxygen does not follow the decrease in hemoglobin and cerebral metabolic rate of oxygen consumption, thus demonstrating better stability to changing hemoglobin content. The low cerebral metabolic rate of oxygen consumption is due to a decrease in arterio-jugular oxygen content difference in anemia, while the cerebral extraction of oxygen does not follow the trend of the arterio-jugular oxygen content difference. Conclusions: In acute brain trauma with acute anemia, calculated arterio-jugular oxygen content difference and cerebral metabolic rate of oxygen consumption tend to be progressively lower, depending on the extent of anemia, which is in disagreement with coma scores. These changes in hemoglobin tend to have an inverse influence on cerebral consumption of oxygen, which, therefore, constitutes an alternative and independent measure of cerebral oxygen consumption under these limiting circumstances.