CONTINUOUS ASSESSMENT OF THE CEREBRAL VASOMOTOR REACTIVITY IN HEAD-INJURY

OBJECTIVE: Cerebrovascular vasomotor reactivity reflects changes in sm ooth muscle tone in the arterial wall in response to changes in transm ural pressure or the concentration of carbon dioxide in blood. We inve stigated whether slow waves in arterial blood pressure (ABP) and intra cranial pressure (ICP) may be used to derive an index that reflects th e reactivity of vessels to changes in ABP. METHODS: A method for the c ontinuous monitoring of the association between slow spontaneous waves in ICP and arterial pressure was adopted in a group of 82 patients wi th head injuries. ABP, ICP, and transcranial doppler blood flow veloci ty in the middle cerebral artery was recorded daily (20- to 120-min ti me periods). A Pressure-Reactivity Index (PRx) was calculated as a mov ing correlation coefficient between 40 consecutive samples of values f or ICP and ABP averaged for a period of 5 seconds. A moving correlatio n coefficient (Mean Index) between spontaneous fluctuations of mean fl ow velocity and cerebral perfusion pressure, which was previously repo rted to describe cerebral blood flow autoregulation, was also calculat ed. RESULTS: A positive PRx correlated with high ICP (r = 0.366; P < 0 .001), low admission Glasgow Coma Scale score (r = 0.29; P < 0.01), an d poor outcome at 6 months after injury (r = 0.48; P < 0.00001). Durin g the first 2 days after injury, PRx was positive (P < 0.05), although only in patients with unfavorable outcomes. The correlation between P Rx and Mean Index (r = 0.63) was highly significant (P < 0.000001). CO NCLUSION: Computer analysis of slow waves in ABP and ICP is able to pr ovide a continuous index of cerebrovascular reactivity to changes in a rterial pressure, which is of prognostic significance.