Intracranial Compliance Concepts and Assessment: A Scoping Review

Abstract

Background: Intracranial compliance (ICC) has been studied to complement the interpretation of intracranial pressure (ICP) in neurocritical care and help predict brain function deterioration. It has been reported that ICC is related to maintaining ICP stability despite changes in intracranial volume. However, this has not been properly translated to clinical practice. Therefore, the main objective of this scoping review was to map the key concepts of ICC in the literature. This review also aimed to characterize the relationship between ICC and ICP and systematically describe the outcomes used to assess ICC using both invasive and non-invasive measurement methods.Methods: This review included the following: (1) population: animal and humans, (2) concept of compliance or its inverse “elastance,” and (3) context: neurocritical care. Therefore, literature searches without a time frame were conducted on several databases using a combination of keywords and descriptors.Results and Discussion: 43,339 articles were identified, and 297 studies fulfilled the inclusion criteria after the selection process. One hundred and five studies defined ICC. The concept was organized into three main components: physiological definition, clinical interpretation, and localization of the phenomena. Most of the studies reported the concept of compliance related to variations in volume and pressure or its inverse (elastance), primarily in the intracranial compartment. In addition, terms like “accommodation,” “compensation,” “reserve capacity,” and “buffering ability” were used to describe the clinical interpretation. The second part of this review describes the techniques (invasive and non-invasive) and outcomes used to measure ICC. A total of 297 studies were included. The most common method used was invasive, representing 57–88% of the studies. The most commonly assessed variables were related to ICP, especially the absolute values or pulse amplitude. ICP waveforms should be better explored, along with the potential of non-invasive methods once the different aspects of ICC can be measured.Conclusion: ICC monitoring could be considered a complementary resource for ICP monitoring and clinical examination. The combination and validation of invasive/non-invasive or non-invasive measurement methods are required.

Intracranial compliance in type 2 diabetes mellitus and its relationship with the cardiovascular autonomic nervous control

“…As a response, pressure rises to adapt to volume variations. However, the ability to adapt is not linear, therefore in these cases, compliance decreases and assumes P2/P1 ratio values greater than 1 ( 14 ). This explains why both T2DM and healthy subjects presented an expected response of the intracranial compliance in the supine position.…”

“…These peaks determine the intracranial compliance through its relationship with cerebral blood volume. Intracranial compliance considers the ability of the brain and the cranial cavity to adapt to (or tolerate) variations in volume and pressure of the intracranial content ( 14 ). The response to the intracranial content cause micro-oscillations in the walls of the skullcap leading to cranial expansion.…”

“…Sympathovagal imbalance leads to dysregulation of cerebral circulation ( 5 , 12 ), although it is not entirely clear whether intracranial compliance is associated with cardiovascular autonomic control ( 13 ) in T2DM. Intracranial compliance can be analyzed through intracranial pressure waveform morphology, which is the relationship between variations in volume and pressure of the intracranial content ( 14 ). The clinical interpretation of intracranial compliance is related to the capacity of the intracranial compartment to accommodate to volume changes.…”

“…The clinical interpretation of intracranial compliance is related to the capacity of the intracranial compartment to accommodate to volume changes. In this sense, changes in intracranial pressure waveform morphology may indicate an impairment in intracranial compliance, which can help predict brain function deterioration ( 14 ).…”

Cerebrospinal fluid micro-volume changes inside the spinal space affect intracranial pressure in different body positions of animals and phantom

“…The ability of craniospinal space to adjust to the volume changes is usually described as spatial compensation (translocation of CSF from the cranial to the spinal space and increase of CSF absorption according to classical hypothesis) and craniospinal compliance (reflects acute volume–pressure relationship, Δ volume/Δ pressure) (Davson et al, 1987 ; Portella et al, 2005 ; Lawley et al, 2015 ; Ocamoto et al, 2021 ; Löfgren and Zwetnow, 1973 ). Craniospinal compliance and spatial capacity determine the slope of the volume–pressure curve.…”