Optical pupillometry in traumatic brain injury: neurological pupil index and its relationship with intracranial pressure through significant event analysis.

: Treatment paradigms for traumatic brain injury (TBI) rely on invasive monitoring of intracranial pressure (ICP) for planning intervention. Optical pupillometry is a non-invasive, objective monitoring method, measuring parameters of pupillary response and displaying a scalar value - a neurological pupil index (NPi). An impaired response on NPi has been tentatively correlated with ICP, through analysis of mean/peak NPi and ICP readings. We sought to evaluate this relationship more closely. : Prospective observational. : We obtained hourly pupillometry readings, alongside ICP values, from 40 patients with TBI requiring invasive ICP monitoring. Significant events were identified for analysis based on the significant aberration of ICP or NPi. : On average, individuals experienced a few significant events. There was a weak relationship between ICP events and a preceding NPi event. The results show that there is a weak but statistically insignificant relationship between NPi and ICP, where reduced pupil reactivity may indicate a raised ICP. The strength of this trend appears to diminish post-decompressive surgery. : Whilst pupillometry may not be a reliable surrogate marker for ICP, NPi may still prove to be a useful tool in a multimodal prognostic assessment of the patient with acute brain injury.