Overview of Monitoring of Cerebral Blood Flow and Metabolism after Severe Head Injury

     J. Paul Muizelaar and Marc L. Schröder

Abstract:   The relationships between cerebral blood flow (CBF), cerebral metabolism (cerebral metabolic rate of oxygen, CMRO₂) and cerebral oxygen extraction (arteriovenous difference of oxygen, AVDO₂) are discussed, using the formula CMRO₂ = CBF x AVDO₂. Metabolic autoregulation, pressure autoregulation and viscosity autoregulation can all be explained by the strong tendency of the brain to keep AVDO₂ constant. Monitoring of CBF, CMRO₂ or AVDO₂ very early after injury is impractical, but the available data indicate that cerebral ischemia plays a considerable role at this stage. It can best be avoided by not "treating" arterial hypertension and not using too much hyperventilation, while generous use of mannitol is probably beneficial. Once in the ICU, treatment can most practically be guided by monitoring of jugular bulb venous oxygen saturation. If saturation drops below 50%, the reason for this must be found (high intracranial pressure, blood pressure not high enough, too vigorous hyperventilation, arterial hypoxia, anemia) and must be treated accordingly.

Can. J. Neurol. Sci. 1994; 21: S6-S11