CEREBRAL BLOOD-FLOW AND OXYGEN-CONSUMPTION IN ACUTE BRAIN INJURY WITHACUTE 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: Prospe ctive, observational study. Setting: Neuroscience intensive care unit (ICU) of a university hospital. Patients: Adults (n = 62) with acute b rain trauma, undergoing serial xenon-133 studies of regional cerebral blood flow and global cerebral oxygen metabolism, along with other rou tine monitoring techniques. Measurements and Main Results: In 173 comb ined studies of blood flow and oxygen metabolism, in the presence of s pontaneous decreases in hemoglobin, cerebral metabolic rate of oxygen consumption and cerebral consumption of oxygen were comparatively eval uated in three groups with different hemoglobin levels. Cerebral metab olic rate of oxygen consumption was calculated as the product of avera ged regional cerebral blood flow and arterio-jugular oxygen content di fference, while cerebral consumption of oxygen was calculated as the p roduct of averaged regional cerebral blood flow and the arterio-jugula r oxyhemoglobin saturation difference, i.e., cerebral extraction of ox ygen. Results indicated that a decrease of hemoglobin content is paral leled by a decrease in cerebral metabolic rate of oxygen consumption, even though the level of consciousness (coma score) is essentially unc hanged across three hemoglobin groups. On the other hand, cerebral con sumption of oxygen does not follow the decrease in hemoglobin and cere bral metabolic rate of oxygen consumption, thus demonstrating better s tability to changing hemoglobin content. The low cerebral metabolic ra te of oxygen consumption is due to a decrease in arterio-jugular oxyge n content difference in anemia, while the cerebral extraction of oxyge n does not follow the trend of the arterio-jugular oxygen content diff erence. Conclusions: In acute brain trauma with acute anemia, calculat ed arterio-jugular oxygen content difference and cerebral metabolic ra te 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 c onsumption of oxygen, which, therefore, constitutes an alternative and independent measure of cerebral oxygen consumption under these limiti ng circumstances.