Transcranial Doppler Systolic Flow Index and ICP-Derived Cerebrovascular Reactivity Indices in Traumatic Brain Injury.

Abstract

To explore relationships between transcranial Doppler (TCD) indices of cerebrovascular reactivity and those derived from intracranial pressure (ICP). Goals: A. Confirm previously described co-variance patterns of TCD/ICP indices, and B. Describe thresholds for Sx (correlation between systolic flow velocity (FVs) and cerebral perfusion pressure (CPP)) associated with outcome. Retrospective cohort of traumatic brain injury (TBI) patients: with TCD and ICP monitoring, we calculated various continuous indices of cerebrovascular reactivity: A. ICP (PRx – correlation between ICP and mean arterial pressure (MAP), PAx – correlation between pulse amplitude of ICP (AMP) and MAP, RAC – correlation between AMP and CPP), B. TCD (Mx – correlation between mean flow velocity (FVm) and CPP, Mx_a – correlation between FVm and MAP, Sx – correlation between FVs and CPP, Sx_a – correlation between FVs and MAP, Dx – correlation between diastolic flow velocity (FVd) and CPP, Dx_a – correlation between FVd and MAP). We assessed the relationships via various statistical techniques, including: principal component analysis , agglomerative hierarchal clustering and k-means cluster analysis. We performed sequential chi-square testing to define thresholds associated with outcome for Sx/Sx_a. Outcome was assessed at 6 months via dichotomized Glasgow Outcome Scores: A. Favourable (GOS 4 or 5) vs. Unfavourable (GOS 3 or less), B. Alive vs. Dead. We analyzed 410 recordings in 347 patients. All analysis confirmed our previously described co-variance of Sx/Sx_a with ICP derived indices. Sx displayed thresholds of -0.15 for unfavourable outcome (p<0.0001) and -0.20 for mortality (p<0.0001). Sx_a displayed thresholds of +0.05 (p=0.019) and -0.10 (p=0.0001) for alive/dead and favourable/unfavourable outcomes. TCD systolic indices are most closely associated with ICP indices. Sx and Sx_a likely provide better approximation of ICP indices, compared to Mx/Mx_a/Dx/Dx_a. Sx provides superior outcome prediction, versus Mx, with defined thresholds. Keywords: continuous autoregulation indices, cerebrovascular reactivity, co-variance, TCD, critical thresholds.