Noninvasive Monitoring of Intracranial Pressure

Increased intracranial pressure (ICP) is one of the major causes of secondary brain ischemia that accompanies a variety of pathological conditions, most notably, traumatic brain injury (TBI), stroke, and intracranial hemorrhages. However, aside from a few Level I trauma centers, ICP monitoring is rarely a part of the clinical management of patients with these conditions because of the invasiveness of the standard monitoring methods (which require insertion of a catheter into the cranium), additional risks they present for patients, high costs associated with the procedure, and the limited access to trained personnel, i.e., a neurosurgeon. Alternative methods have therefore been sought with which ICP can be measured noninvasively. This article reviews nearly 30 such methods patented over the past 25 years, which included ultrasound "time-of-flight" techniques, transcranial Doppler, methods based on acoustic properties of the cranial bones, EEG, MRI, tympanic membrane displacement, oto-acoustic emission, ophthalmodynamometry, and ultrasound measurements of optic nerve sheath diameter. At present, none of the methods is sufficiently accurate to allow for routine clinical use although several hold promise. Future developments should integrate further refinements of the existing methods, combined use of multiple sensors and/or technologies, and large clinical validation studies on relevant populations. Keywords: Intracranial pressure, ICP, noninvasive, non-invasive, monitoring, patents