Validation of a Noninvasive Approach for Cerebrospinal Compliance Monitoring

Intracranial pressure (ICP) monitoring is a cornerstone of neurointensive care. However, some limitations of invasive techniques for ICP monitoring to acknowledge are the risk for complications and the lack of robust evidence supporting individualized ICP safety thresholds. Cerebrospinal compliance (CSC) may serve as a more reliable indicator of brain health than ICP alone. Previously, intracranial compliance (Ci), was described as a mathematical model from invasive ICP to assess CSC, using ICP waveform amplitudes and cerebral arterial blood volume (CaBV) waveform amplitudes via transcranial Doppler (TCD). This study aimed to compare Ci with a surrogate parameter based on CaBV waveform amplitudes and pulsatile micrometric skull waveforms (Skw) amplitudes. This noninvasive parameter was named Bcomp.

Neurocritical patients undergoing ICP monitoring were evaluated using TCD and the skull micrometric deformation sensor (B4C). ICP waveform (from invasive ICP probes) and Skw (from noninvasive B4C) were analyzed to extract pulse amplitudes, whereas TCD provided cerebral blood velocities from the middle cerebral arteries for CaBV calculation. CSC was measured using the volume/pressure relationship, with CaBV amplitude serving as the volume surrogate, and ICP and B4C pulse amplitudes as surrogates for ICP values. Agreement and correlation analysis was calculated between Ci and Bcomp.

Data from 71 patients were analyzed, with 68% of the sample having suffered traumatic brain injury. Maximum CaBV was significantly delayed in patients with poor CSC (p < 0.001). Ci and Bcomp showed strong agreement and linear correlation (mean difference of - 0.28 and Spearman correlation of 0.88, p < 0.001).

Using CaBV, which reflects changes in arterial blood volume during the cardiac cycle and Skw pulse amplitudes, Bcomp demonstrated high agreement and correlation with Ci, defined as the product of CaBV and ICP pulse amplitude. The observed shift in CaBV among patients with poor CSC suggests that this vascular marker is influenced by intracranial resistance. These findings are promising for the real-time, noninvasive assessment of CSC in clinical settings and warrant further research.