Validity of Quantitative Pupillometry in Neurocritical Care and Correlation With Intracranial Pressure : an Observational, Uni-institutional Study

Traumatic brain injury (TBI) is a leading cause of death and disability in adults worldwide. Severe TBI, defined as a Glasgow Coma Score (GCS) 8, is associated with mortality as high as 30-40%. It is established that the major determinant of outcome following TBI and target of medical interventions is secondary brain injury, primarily cerebral ischaemia. It is due to a combination of intracranial hypertension (ICH), systemic hypotension, hypoxia, hyperpyrexia, hypercapnia and hypoglycaemia, all have been shown to independently worsen survival after TBI. ICH refers to rise in pressure inside the rigid skull (intracranial pressure (ICP)), which reduces blood flow and oxygen to the brain. ICP values over 20-25mmHg are indicative of ICH. Accordingly, treatment of these patients centres on controlling ICP, improving cerebral blood flow (CBF) and oxygenation.

Monitoring pupil size and its light reflex mechanism is an integral part of non-invasive clinical monitoring in patients with severe brain injury in NCCUs globally. Abnormalities in pupillary response or size asymmetry are associated with neurological deterioration and poor outcome. In addition, studies have shown a strong correlation with brainstem oxygenation and blood flow.

A study evaluating pupil response and ICP showed that changes in pupils were detected even in patients with normal ICP. Crucially, they suggested that abnormalities in posterior frontal and temporal regions of the brain may occur even when the ICP is normal. Given the indispensable role of these parameters, there is considerable impetus to ensure they are measured accurately.

The invetigator's study aims to compare the use of standard pen torch versus quantitative pupillometer for pupil assessment in severely brain injured patients in NCCU. This data could establish whether currently practised pen torch assessment is inadequate for clinical practice. The investigators also propose to study whether pupil response (NPi) changes with rising ICP. This group of patients have invasive monitoring in place as standard care and provides an important opportunity to study this relationship. This has the potential to allow early, non-invasive detection of neurological deterioration and as such, indication for timely intervention in the first instance. It also allows scope for development of this tool across emergency departments and even pre-hospital care settings.

The primary aims of this study are twofold. First, to compare the accuracy and reliability of the pupillometer device (NPi 200) versus the conventional pen-torch technique in measuring pupil response in patients with severe TBI in NCCU.