Relationship between cerebral near-infrared spectroscopy signals and intracranial pressure: a systematic scoping review of the human and animal literature

<i>Objective.</i>Monitoring of intracranial pressure (ICP) in a clinical environment is critically important to the stability of patients with various acute neurological illnesses and injury including ischemic stroke, hemorrhagic stroke, brain tumor, and traumatic brain injury. This is because changes in ICP can cause significant stress on the brain and surrounding tissue through complications such as cerebral ischemia or hemorrhage in the surrounding area. Most ICP measurement techniques are invasive, expensive, and have poor spatial resolution. There has been some preliminary evidence to suggest that regional oxygen saturation (rSO₂) measured non-invasively by near-infrared spectroscopy (NIRS) has a statistical link to invasively obtained ICP. Given the limited exploration of this potential link, this scoping review (ScR) aims to investigate the current body of literature exploring the association between cerebral NIRS measurements and ICP.<i>Approach.</i>A comprehensive investigation was conducted across six major databases, with accordance to the preferred reporting items for systematic reviews and meta-analyzes guidelines, in order to evaluate the primary question of: What is the relationship between NIRS-derived cerebral signals and ICP?.<i>Main results</i>. The search process identified 3791 distinct articles. After screening based on the predefined criteria, 10 studies were deemed eligible for inclusion. An additional two studies were identified by screening the citation lists of the included studies. Overall, the collection of articles selected for this systematic ScR indicates a potential positive correlation between some cerebral NIRS variables and ICP; however, significant discrepancies and significant limitations exist in the literature.<i>Significance.</i>This review identifies a significant knowledge gap in the current understanding of how non-invasive NIRS metrics relate to ICP and highlights the importance of conducting additional experimentation in the field.