Intracranial pressure monitoring

Intracranial pressure monitoring is exactly what the name says: measuring how much pressure there is inside the skull. Under normal conditions that pressure runs from seven to fifteen millimeters of mercury.

The reason to measure it comes from an old and simple idea, the Monro-Kellie doctrine. The skull is bone: it does not stretch and it does not compress. Since the container never changes size, if one of its contents grows, another has to give up space. The skull does not stretch: whatever one thing takes up, it takes from another. The main buffers are the cerebrospinal fluid, the fluid that surrounds the brain, and the blood: they provide room to maneuver.

To measure it, you have to go in. A hole is made in the bone and the sensor goes in through it: it can be a catheter inside the lateral ventricle, one of the cavities where cerebrospinal fluid circulates, or a sensor placed in the brain tissue itself, or a fiber-optic monitor.