Researchers have developed a probe that contains infrared light sources that can illuminate the deep brain tissue of the frontal lobe. Photodetectors in the probe detect the backscattered light, which is modulated by pulsation of the cerebral arteries. Changes in the extramural arterial pressure affect the morphology of the recorded optical pulse, so analysis of the acquired signal using an appropriate algorithm could enable the calculation of the intracranial pressure noninvasively (nICP), which would be displayed to clinicians continuously.

This pilot study is the first evaluation of the device in patients in who the gold standard comparator of invasive ICP was available. The acquisition of pulsatile optical signals was performed for up to 48 hours in each of the 40 patients who were undergoing invasive ICP monitoring as part of their normal medical treatment.

Features of the optical signals would be analysed offline. A machine vector support algorithm would be implemented, with the aim of estimating ICP noninvasively and compared to the gold standard of synchronously acquired invasive ICP data.

Traumatic brain injury (TBI) is the most common cause of death and disability in the under 40 age group both in the United Kingdom and worldwide, and prevalence is increasing. The mainstay of severe TBI management is intracranial pressure (ICP) measurement. ICP is defined as the pressure within the skull and brain. TBI often causes a rise in ICP as the brain swells within the rigid skull and therapy is directed at keeping this pressure at an acceptable level with medications or surgery. Very high ICP may lead to further brain damage resulting in increased disability or death.

Existing techniques to measure ICP involve placing an electrical sensor into the brain tissue through a small hole drilled in the skull. This procedure risks infection and bleeding into the brain and can only be performed by a neurosurgeon. Therefore, there is a vital demand to develop non-invasive technologies that will allow measuring the ICP without inserting a sensor in the brain. This technology will decrease the risks, permit monitoring outside the hospital (eg in an ambulance) and reduce the costs. It will also increase the indication for ICP monitoring to include other conditions (e.g. stroke or brain tumours) which are not currently monitored.

The proposed non-invasive ICP (nICP) monitor works by shining a harmless light into the brain through the skull. The developed sensor was attached to the skin of the forehead and recorded optical signals (known as photoplethysmography (PPG)) from the brain, which are related to changes in the ICP. This pilot aims to build the first clinical database of nICP signals in intensive care patients. The acquisition of an extensive set of signals would allow the generation of advanced algorithms and Machine Learning (ML) models utilising optical signal feature extraction techniques. The resulting model will be implemented in translating the optical signals into absolute measurements of ICP.

Inclusion Criteria:

• Patient admitted to the Royal London Hospital who is having invasive ICP monitoring as part of their normal medical care
• Subject is able to understand the risks and potential benefits of participating in the study and is willing to provide written informed consent. If the patient is unconscious, and a consultee is not available then a professional consultee (a doctor looking after the patient who is not involved in the trial) will assent to inclusion in the trial and non-invasive ICP monitoring will be performed.

Exclusion Criteria:

• Patients with decompressive craniectomy

Only the final results of the nICP safety and accuracy would be published. Any individual participant data would be available to other researchers.