Noninvasive Intracranial Pressure (ICP) Monitor
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. As the skull is a closed cavity containing water and other largely incompressible material, even minor swelling can cause significant increases in ICP (intracranial pressure). Various strategies exist to arrest or reverse the pressure in the brain due to head trauma, so monitoring the ICP is a vital tool in the management of severe head injuries.
A new non-invasive system for continuous monitoring of ICP via a forehead-mounted probe has been developed. 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.