Complexity of intracranial pressure correlates with outcome after traumatic brain injury

Abstract

This study applied multiscale entropy analysis to investigate the correlation between the complexity of intracranial pressure waveform and outcome after traumatic brain injury. Intracranial pressure and arterial blood pressure waveforms were low-pass filtered to remove the respiratory and pulse components and then processed using a multiscale entropy algorithm to produce a complexity index. We identified significant differences across groups classified by the Glasgow Outcome Scale in intracranial pressure, pressure-reactivity index and complexity index of intracranial pressure (P < 0.0001; P = 0.001; P < 0.0001, respectively). Outcome was dichotomized as survival/death and also as favourable/unfavourable. The complexity index of intracranial pressure achieved the strongest statistical significance (F = 28.7; P < 0.0001 and F = 17.21; P < 0.0001, respectively) and was identified as a significant independent predictor of mortality and favourable outcome in a multivariable logistic regression model (P < 0.0001). The results of this study suggest that complexity of intracranial pressure assessed by multiscale entropy was significantly associated with outcome in patients with brain injury.

Figure 1

The illustration of (A) the coarse graining procedure and (B) sample entropy. For length m = 2, two sequences (dotted circle) match the first two data points and one sequence (circle) matches the first three data points (length m + 1). This matching process is repeated for the next two data points and then all sequences to determine the total number of matches of length m and m + 1. Sample entropy is calculated as the negative natural logarithm of the ratio between the number of length m + 1 matches and the number of length m matches.

Figure 2

Time-related changes of intracranial pressure (ICP), arterial blood pressure (ABP), cerebral perfusion pressure (CPP) and pressure reactivity index (PRx) during (A) plateau wave and (B) refractory intracranial hypertension. Multiscale entropy (MSE) during baseline (arrow) and increased intracranial pressure (arrowhead) in (C) 10 episodes of plateau wave and (D) seven episodes of refractory intracranial hypertension. (E) Complexity index of intracranial pressure. Results are the mean ± SEM. SE = sample entropy.

Figure 3

Calculated parameters in different Glasgow Outcome Scale (GOS) groups. (A) Intracranial pressure (ICP), (B) arterial blood pressure (ABP), (C) cerebral perfusion pressure (CPP), (D) pressure reactivity index (PRx) and (E) complexity index of intracranial pressure (ICP-CI). Results represent the mean and 95% confidence intervals. Symbols express the difference between groups in one-way ANOVA followed by Bonferroni post hoc analysis with a confidence level of P < 0.05. *Group differed from three other groups. †Dead differed from good outcome and moderate disability.

Figure 4

Empirical regression plots for all patients. (A) Complexity index of intracranial pressure (ICP-CI) versus mean intracranial pressure (ICP). (B) Complexity index of intracranial pressure versus cerebral perfusion pressure (CPP). (C) Pressure-reactivity index (PRx) versus cerebral perfusion pressure. Results are mean ± SEM.