Abstract
BackgroundThe pulse waveform of intracranial pressure (ICP) is its distinctive feature almost always present in the clinical recordings. In most cases, it changes proportionally to rising ICP, and observation of these changes may be clinically useful. We introduce the higher harmonics centroid (HHC) which can be defined as the center of mass of harmonics of the ICP pulse waveform from the 2nd to 10th, where mass corresponds to amplitudes of these harmonics. We investigate the changes in HHC during ICP monitoring, including isolated episodes of ICP plateau waves.Material and methodsRecordings from 325 patients treated between 2002 and 2010 were reviewed. Twenty-six patients with ICP plateau waves were identified. In the first step, the correlation between HHC and ICP was examined for the entire monitoring period. In the second step, the above relation was calculated separately for periods of elevated ICP during plateau wave and the baseline.ResultsFor the values averaged over the whole monitoring period, ICP (22.3 ± 6.9 mm Hg) correlates significantly (R = 0.45, p = 0.022) with HHC (3.64 ± 0.46). During the ICP plateau waves (ICP increased from 20.9 ± 6.0 to 53.7 ± 9.7 mm Hg, p < 10−16), we found a significant decrease in HHC (from 3.65 ± 0.48 to 3.21 ± 0.33, p = 10−5).ConclusionsThe good correlation between HHC and ICP supports the clinical application of pressure waveform analysis in addition to the recording of ICP number only. Mean ICP may be distorted by a zero drift, but HHC remains immune to this error. Further research is required to test whether a decline in HHC with elevated ICP can be an early warning sign of intracranial hypertension, whether individual breakpoints of correlation between ICP and its centroid are of clinical importance.
Highlights
Intracranial compliance (ICC) describes the capacity of intracranial compartments to contain an additional volume with no significant change in intracranial pressure (ICP) [30]
It was shown that a decrease in higher frequency centroid (HFC) was associated with refractory intracranial hypertension [13]. This early observation has never been confirmed in the practice of neurosurgery and neurocritical care worldwide. We introduced another metric of the ICP pulse waveform which is the higher harmonics centroid (HHC) [5, 35]
We aim to investigate the correlations between HHC and ICP, arterial blood pressure (ABP), cerebral perfusion pressure (CPP), heart rate (HR), and PRx, the cerebral pressure reactivity index [14] for (1) the entire monitoring time performed in patients after traumatic brain injury and (2) during isolated ICP plateau waves and at their corresponding baseline episodes
Summary
Intracranial compliance (ICC) describes the capacity of intracranial compartments to contain an additional volume with no significant change in intracranial pressure (ICP) [30]. Works reported that changes in ICP pulse waveform indicate changes in ICC, which may be clinically useful above the traditionally considered ICP value itself [3, 25, 28, 29, 33, 34]. It was reported that “the spontaneous increase in intracranial pressure (ICP) is accompanied by a disproportionate elevation of the cerebrospinal fluid pulse wave components P2 and P3, resulting in changes of the shape of the pulse wave. It first becomes rounded and, at higher ICP values, it acquires a pyramidal shape” [8] (Fig. 1b). Further research is required to test whether a decline in HHC with elevated ICP can be an early warning sign of intracranial hypertension, whether individual breakpoints of correlation between ICP and its centroid are of clinical importance
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