Continuous Measurement in Neurocritical Care of Cerebral Blood Flow (CBF) Calculated from ICP and Central Venous Pressure

<b>Background/Objectives:</b> In neurocritical care, usually, the only continuous measurement of brain pathophysiology is intracranial pressure (ICP). The objective of this study was to find the relationship between cerebral blood flow (CBF) and parameters usually measured in neurocritical care, mainly central venous pressure and ICP. <b>Methods:</b> If the venous outflow of the CBF is considered, the CBF is controlled only by two parameters, the <i>rICP</i> (the ICP minus the venous blood pressure in the venous sinus at its outflow) and the <i>Rv</i> (the flow resistance of the soft-walled veins). For the <i>rICP</i>, the sinus blood pressure can be calculated from the central venous pressure (measured at the same horizontal level as the ICP) and the cervical venous flow resistance. For the <i>Rv</i>, the systolic ICP increase indicates the systolic arterial inflow volume, which then flows out before the diastole. The mean ICP increase divided by the mean outflow of the increased blood volume gives the <i>Rv</i>. This method of calculating the CBF by dividing the <i>rICP</i> by the <i>Rv</i> was named <b>CBF(1)</b>. For validation of <b>CBF(1)</b>, data from nine subjects in an open study were used. The data were ICP and MR blood flow measurements of arterial inflow and jugular vein outflow. Since the <i>rICP, Rv</i>, and CBF were unknown, an iterative method was needed to calculate these parameters. <b>Results:</b> The observed <i>Rv</i> and <i>rICP</i> values showed a close correlation, which indicated that CBF was dependant on the <i>rICP</i> only. Consequently, the comparison between the data in the study of the nine subjects, and the calculated values from <b>CBF(1)</b>, boiled down to a comparison between the supine ICP values and the calculated rICP. The comparison showed that the rICP and supine ICP had highly significant similarity, and that the <b>CBF(1)</b> method was validated. <b>Conclusions:</b> A method for CBF measurement from ICP data in neurocritical care was found.