Long-term intracranial pressure monitoring

Continuous or intermittent measurement of intracranial pressure (ICP) is important in patients at risk for raised ICP. Indications exist for short- and long-term measurements. The various methods used for short-term monitoring are discussed with their relative advantages and disadvantages. For long-term measurements of ICP use of a completely implantable telemetric epidural pressure transducer is indicated. No such device is commercially available. We have developed an inexpensive passive telemetric transducer for this purpose. Results obtained up till now have demonstrated its reliability for measurements of two to three months duration. The life span of the device is limited by degrading of the epoxy utilized for sealing of the titanium pressure sensing part to the radiolucent ceramic cap of the transducer, causing leakage of water into the transducer and false low measurements. Because of these problems new hermetic sealing techniques were tested. Both active metal brazing and glass bonding yielded good results and hermetic sealing could be obtained. The metal to ceramic bonding presented is generally applicable within the design of implants. Besides the technical progress reported, the experience with clinical use in 12 patients is presented.