Low-resolution pressure reactivity index and its derived optimal cerebral perfusion pressure in adult traumatic brain injury: a CENTER-TBI study

Abstract

Background: After traumatic brain injury (TBI), brain tissue can be further damaged when cerebral autoregulation is impaired. Managing cerebral perfusion pressure (CPP) according to computed "optimal CPP" values based on cerebrovascular reactivity indices might contribute to preventing such secondary injuries. In this study, we examined the discriminative value of a low-resolution long pressure reactivity index (LPRx) and its derived "optimal CPP" in comparison to the well-established high-resolution pressure reactivity index (PRx).

Methods: Using the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) study dataset, the association of LPRx (correlation between 1-min averages of intracranial pressure and arterial blood pressure over a moving time frame of 20 min) and PRx (correlation between 10-s averages of intracranial pressure and arterial blood pressure over a moving time frame of 5 min) to outcome was assessed and compared using univariate and multivariate regression analysis. "Optimal CPP" values were calculated using a multi-window algorithm that was based on either LPRx or PRx, and their discriminative ability was compared.

Results: LPRx and PRx were both significant predictors of mortality in univariate and multivariate regression analysis, but PRx displayed a higher discriminative ability. Similarly, deviations of actual CPP from "optimal CPP" values calculated from each index were significantly associated with outcome in univariate and multivariate analysis. "Optimal CPP" based on PRx, however, trended towards more precise predictions.

Conclusions: LPRx and its derived "optimal CPP" which are based on low-resolution data were significantly associated with outcome after TBI. However, they did not reach the discriminative ability of the high-resolution PRx and its derived "optimal CPP." Nevertheless, LPRx might still be an interesting tool to assess cerebrovascular reactivity in centers without high-resolution signal monitoring.

Trial registration: ClinicalTrials.gov Identifier: NCT02210221. First submitted July 29, 2014. First posted August 6, 2014.

Keywords: CPPopt; Cerebral autoregulation; Cerebral perfusion pressure; Cerebrovascular reactivity; Traumatic brain injury.

Conflict of interest statement

LR received a scholarship from the CENTER-TBI study to visit the Brain Physics Lab in Cambridge. MC and PS receive part of the licensing fee for the ICM+ software. MC is supported by the NIHR Biomedical Research Centre Cambridge. The remaining authors have nothing to disclose.

Figures

Fig. 1

a Spearman’s correlation between LPRx and PRx. b Bland-Altman plot for agreement between PRx and LPRx showing mean bias (solid line), zero difference (thin dashed line), and 95% lines of agreement (thick dashed lines)

Fig. 2

Histograms showing the absolute (a, b) and relative (c, d) proportion of patients with fatal outcome for different LPRx and PRx values

Fig. 3

AUCs for the prediction of mortality for different regression models. a LPRx and PRx. b IMPACT variables with the addition of LPRx and PRx. c ΔCPPoptLPRx and ΔCPPoptPRx. d IMPACT variables with the addition of ΔCPPoptLPRx and ΔCPPoptPRx

Fig. 4

AUCs for the prediction of mortality and unfavorable outcome over the early post-traumatic time course. a LPRx and PRx in regard to mortality. b LPRx and PRx in regard to unfavorable outcome. c ΔCPPoptLPRx and ΔCPPoptPRx in regard to mortality. d ΔCPPoptLPRx and ΔCPPoptPRx in regard to unfavorable outcome. The only significant difference was observed at day 6 between LPRx and PRx (*p = 0.007)

Fig. 5

Bar graphs showing the proportion of fatal outcome (a, b) and severe disability (c, d) in patients with a mean deviation of at least 5 mmHg below or above their CPPoptLPRx or CPPoptPRx