Abstract
BackgroundTwo transcranial Doppler (TCD) estimators of cerebral arterial blood volume (CaBV) coexist: continuous outflow of arterial blood outside the cranium through a low-pulsatile venous system (continuous flow forward, CFF) and pulsatile outflow through regulating arterioles (pulsatile flow forward, PFF). We calculated non-invasive equivalents of the pressure reactivity index (PRx) and the pulse amplitude index PAx with slow waves of mean CaBV and its pulse amplitude.MethodsAbout 273 individual TBI patients were retrospectively reviewed. PRx is the correlation coefficient between 30 samples of 10-second averages of ICP and mean ABP. PAx is the correlation coefficient between 30 samples of 10-second averages of the amplitude of ICP (AMP, derived from Fourier analysis of the raw full waveform ICP tracing) and mean ABP. nPRx is calculated with CaBV instead of ICP and nPAx with the pulse amplitude of CaBV instead of AMP (calculated using both the CFF and PFF models). All reactivity indices were additionally compared with Glasgow Outcome Score (GOS) to verify potential outcome-predictive strength.ResultsWhen correlated, slow waves of ICP demonstrated good coherence between slow waves in CaBV (>0.75); slow waves of AMP showed good coherence with slow waves of the pulse amplitude of CaBV (>0.67) in both the CFF and PFF models. nPRx was moderately correlated with PRx (R = 0.42 for CFF and R = 0.38 for PFF; p < 0.0001). nPAx correlated with PAx with slightly better strength (R = 0.56 for CFF and R = 0.41 for PFF; p < 0.0001). nPAx_CFF showed the strongest association with outcomes.ConclusionsNon-invasive estimators (nPRx and nPAx) are associated with their invasive counterparts and can provide meaningful associations with outcome after TBI. The CFF model is slightly superior to the PFF model.
Highlights
This article is part of the Topical Collection on Neurosurgical intensive careCambridge, Cambridge, U.K. 5 Section of Neurosurgery, Department of Surgery, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, CanadaThe pressure reactivity index (PRx) is a common descriptor of cerebrovascular reactivity (CVR) following traumatic brain injury (TBI)
Slow waves of intracranial pressure (ICP) and cerebral arterial blood volume (CaBV) in most cases appeared well-synchronized in time (Fig. 1A, top panel)
It must be noted that the outliers derived from the results shown in Fig. 2 are due to the varying blood pressures exhibited by patients in the TBI database
Summary
The pulse amplitude index (PAx) is another index of cerebrovascular reactivity, which theoretically can outperform PRx when the compliance of the cranial space is increased (i.e., after craniectomy, with CSF leakages, etc.). Acta Neurochir (2020) 162:337–344 the pulse amplitude of ICP (AMP) with changes in mean ABP (as the moving correlation coefficient of 30 samples of 10-second averages of AMP and mean ABP). Both PRx and PAx can be only calculated when ICP is monitored. All reactivity indices were compared with Glasgow Outcome Score (GOS) to verify potential outcome-predictive strength
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