Head injuries are a significant cause of injury and death, with approximately 50,000 cases of severe traumatic brain injury per year in the UK, the majority leading to death or severe disability. Cerebral damage sustained at the time of impact is referred to as primary injury and is irreversible and best treated by prevention (seatbelts, cycle helmets etc). Secondary brain injury occurs after the initial injury and is defined as damage arising from the body’s physiologic response to the primary injury. This may be as a result of bleeding or swelling of brain tissue. As the skull is a closed cavity containing water and other largely incompressible material, even minor swelling can cause significant increase in ICP. Initially, cerebrospinal fluid and venous blood are displaced (as described in the Munro-Kellie doctrine) but once these reservoirs are exhausted, small increases in pressure are transmitted directly to the brain tissue, compromising the arterial blood supply and reducing oxygen and glucose delivery to the brain tissue. This in turn results in further brain swelling which further compromises blood supply. Severe hypoxic brain injury can result, leading to irreversible brain damage. Various strategies exist to arrest or reverse this process so monitoring ICP is a vital tool in the management of severe head injuries.
This project is developing a new non-invasive system for continuous monitoring of intracranial pressure (ICP) via a forehead-mounted probe. Although the cranium is a closed rigid structure, interrogation using infrared light provides a potential ‘window’ for monitoring cerebral haemodynamics. The probe contains infrared light sources that can illuminate the deep brain tissue of the frontal lobe, while photodetectors in the probe detect the backscattered light, which is modulated by pulsation of the cerebral arteries. Changes in the pressure surrounding the cerebral arteries affect the morphology of the recorded optical pulse, so analysis of the acquired signal using an appropriate algorithm will enable calculation of non-invasive ICP (nICP) that can be displayed continuously to clinicians.
The “gold standard” technique for ICP monitoring is a catheter inserted into the frontal horn lateral ventricle via a right frontal burr hole, connected to a pressure transducer via a fluid-filled catheter. It has the advantage of allowing therapeutic drainage of CSF and administration of drugs however insertion may be difficult if the ventricles are small and even if performed in a sterile environment, infections and bleeding are significant potential risks.
The reported nICP could provide invaluable screening at the triage stage, indicating intracranial hypertension requiring imaging or intervention (such as CSF (Cerebrospinal Fluid) drainage). It could also provide effective guidance for head injury management, notably ICP-targeted treatment regimes. Ultimately this could lead to significant improvements in secondary injury-related mortality, length of hospital stay and reduced post-trauma disability. It could also find application in causes of non-trauma related intracranial hypertension including meningitis, hepatic encephalopathy, hydrocephalus and severe migraine.
The prototype currently in development takes the form of a stand-alone monitor connected to a notebook computer, which records the signals and calculates nICP in real time, and is has been shown to detect changes in pressure within an in vitro intracranial tissue model. The initial stages of the project will focus on further development of the probe geometry, instrumentation and calibration algorithms. Results from a laboratory evaluation will feed back to further design iterations and a clinical prototype will be manufactured at City University.
The project is still in development
The technology allows rapid assessment of the patient’s condition noninvasively and this reduces the significant risk of side effects whilst reducing the cost of monitoring. This makes the technology advantageous in situations where conventional assessment of intracranial pressure may not be considered because of the invasive nature of the procedure and therefore this approach could become a standard procedure in all situations where concussion has occurred.
The device, which will be suitable for use in the pre-hospital environment, emergency departments and intensive care units, will be evaluated in healthy volunteers to assess the performance, reliability and reproducibility of the acquired data. A medical device portfolio comprising design details along with evaluation data will be submitted to the MHRA for approval as a CE-marked medical device. Following this a pilot clinical trial in patients will take place comparing the recorded nICP values with reference data recorded from an intraventricular catheter. Data collected from in vitro, volunteer and clinical studies, will support further development in partnership with a medical device manufacturer to produce a commercially available nICP monitoring system.
In addition to monitoring Traumatic Brain Injuries in a conventional clinical setting this device could also facilitate research and clinical monitoring in non-head injury medicine, such as liver failure, migraine, diabetes, anaesthesia, intensive care, renal medicine etc.
Aside from trauma, management of other conditions associated with intracranial hypertension such as hydrocephalus, severe migraine and meningitis, could benefit from nICP monitoring. In many cases, especially borderline cases or those in early stages, the risk of invasive ICP monitoring is not justifiable; nevertheless intracranial monitoring could provide invaluable clinical information. A non-invasive ICP monitor would also be an invaluable research tool both for investigation of pathophysiology and for assessment of the effectiveness of treatments for intracranial hypertension. There may also be opportunities for research into ICP responses in high altitude or space medicine.