Assessment of the variation in cerebrovascular reactivity in head injured patients

Several indices have been reported which correlate with autoregulatory function [2, 3]. However, before critical thresholds for targeting therapy can be defined, a better understanding of the inherent variability of cerebrovascular reactivity as measured by these indices is required. In this study, patients had BP, ICP and bilateral MCA TCD velocity monitored before, during and after BP and CO2 challenges, applied in a random order, with measurements taken within 48 hours of injury. Four indices of reactivity were calculated: the PRx, the CORRx and the FVreact & ICPreact. At 48 hours post-injury inter-patient variation in cerebrovascular reactivity, as measured by these indices, is large and injury specific factors remain important determinants of the variance. Within patient analysis has identified instances where the combined monitoring of the PRx and the CORRx may provide information about the function of pressure autoregulation and further study of the combined use of these two indices of reactivity is warranted.