Monitoring of regional cerebral blood flow (CBF) in acute head injury by thermal diffusion.

During the last few years continuous measurements of CBF by means of a thermal diffusion blood flow probe have been proposed as a possible means for monitoring the patient's CBF in a clinical setting. Also, it has been suggested that continuous CBF data from head injured patients can be correlated with other continuously recorded clinical parameters, such as ICP and blood pressure, in order to clarify pathophysiological mechanisms such as "plateau-waves". We measured regional cortical blood flow continuously with a thermal diffusion flow probe in 13 comatose head injured patients after undergoing craniotomy for evacuation of a traumatic intracranial mass lesion in order to assess the reliability and usefulness of the method. In seven patients stable Xenon-CT CBF studies were performed with the flow probe in place, in order to compare the two methods. The continuous blood flow values did not correlate with regional or global stable Xenon-CT values. These results indicate that continuous monitoring of CBF with the thermal diffusion method as currently used cannot be used in the clinical management of the patient. Further research will have to be directed to the question as to whether changes in CBF are reliably measured with this method. If this is true, the thermal diffusion flow probe with its high temporal resolution may still be useful in investigating pathophysiological mechanisms such as interaction between CBF, ICP, mean arterial blood pressure (MABP), and end-expiratory CO2 (etCO2).