CBF in head injury.

In the last few years the possibility of measuring CBF by means of intravenous isotop injection technique and portable monitor has made the use of measuring CBF in the clinical setting of the brain injured patient of current interest. However, knowledge about the hemodynamics of the head trauma is inevitable for the interpretation of the CBF results. In this communication a short outline of the results obtained during the last decades studies about the hemodynamic of the damaged brain is given. The essence of these studies seems to be: The local level of CBF do not indicate the severity of the brain injury, as low as well as high flow may be seen initially in severely injured brain tissue. The oxygen uptake (CMRO2) is related to the severity of the brain trauma, as low CMRO2 correlate to poor clinical condition. In severely damaged brain tissue the autoregulation may appear normal (false autoregulation) whereas the autoregulation in moderately damaged tissue may appear impaired for weeks. The carbon dioxide response (CO2) is only impaired if the brain tissue is severely damaged. Thus, low CMRO2 and dissociation between apparently normal autoregulation and impaired CO2 response seem to predict poor outcome.