Exploring Cerebrospinal Compensatory Zones Using a Noninvasive Approach.

Background: Intracranial compliance (ICC) reflects the balance among intracranial volume components. Recent technological advances enable continuous, noninvasive assessment of ICC in neurocritical care settings. In this study, we aimed to correlate noninvasive ICC parameters derived from intracranial pressure (ICP) waveform morphology with the established amplitude-pressure index (RAP index), which is calculated using invasive ICP monitoring.

Methods: Patients with traumatic brain injury underwent ventricular ICP monitoring. Simultaneously, ICP values and waveform characteristics were recorded using an external skull microdynamics sensor (brain4care) that provides surrogate waveform parameters, including the P2/P1 ratio and time-to-peak (TTP). The RAP index was calculated using dedicated software based on ICP values and pulse amplitude and was used to categorize patients into three groups: (1) adequate ICC, (2) compromised ICC, and (3) exhausted ICC. Noninvasive parameters (P2/P1 ratio and TTP) were then analyzed in relation to RAP index groupings.

Results: A total of 61 patients were included. Group 1 (adequate ICC) had a median ICP of 12.3 ± 5.4 mm Hg, a P2/P1 ratio of 1.06 ± 0.3, and a TTP of 0.18 ± 0.09 s. Group 2 (compromised ICC) had a median ICP of 13 ± 6.4 mm Hg, a P2/P1 ratio of 1.15 ± 0.32, and a TTP of 0.23 ± 0.07 s. Group 3 (exhausted ICC) had a median ICP of 19.45 ± 5.9 mm Hg, a P2/P1 ratio of 1.31 ± 0.26, and a TTP of 0.25 ± 0.05 s. Regression analysis revealed a statistically significant association between the noninvasive parameters and RAP index-based ICC classification (p < 0.0001).

Conclusions: This study demonstrates a significant correlation between the RAP index and noninvasive ICP waveform-derived parameters, such as the P2/P1 ratio and TTP. These findings suggest that such noninvasive measures may serve as reliable indicators of ICC status. The critical ICP cut-off per RAP was 19.45 mmHg, below the current threshold for therapy escalation according to TBI guidelines. Although further prospective validation is required, this approach has the potential to facilitate earlier intervention before ICC deterioration and enable noninvasive monitoring, possibly improving outcomes in neurocritical care.

Trial registration: NCT03144219. Registered 15 June 2017, http://www.

Clinicaltrials: gov/NCT03144219 .

Clinical trial registration: ClinicalTrials.gov identifier: NCT03144219.