New concepts in intracranial compliance: pathophysiology, monitoring and clinical implications

Purpose of review This review synthesizes recent advancements in understanding intracranial compliance (ICC) pathophysiology, explores novel monitoring techniques, and discusses their evolving clinical implications. We highlight how a shift from static intracranial pressure (ICP) thresholds to dynamic ICC assessment is transforming the management of acute brain injury. Recent findings ICC is the brain's ability to accommodate volume changes without significant ICP elevation, is a critical determinant of outcome in neurocritical care. The paradigm in ICC is evolving from a focus on absolute ICP values to a dynamic, continuous assessment of the brain's compensatory capacity. Emerging concepts extend the classical Monro-Kellie doctrine, incorporating the dynamic roles of cerebrospinal fluid circulation, including the glymphatic system, in maintaining intracranial homeostasis. Integrating new pathophysiological insights with advanced monitoring tools holds immense potential to refine clinical decision-making, enabling more proactive and personalized interventions, ultimately improving outcomes for patients with acute brain injury. Summary To achieve such goal, both invasive and noninvasive advanced monitoring techniques now provide real-time insights into ICC status. ICP waveform analysis offers granular information on compensatory reserve and cerebral autoregulation. Noninvasive methods, such as cranial micro-deformation sensors and transcranial Doppler-derived parameters offer accessible bedside assessment. These tools, alongside others such as optic nerve sheath ultrasound and pupillometry, facilitate earlier detection of decompensation, guide individualized therapy and improve prognostication.