Clinical evaluation of long-term epidural monitoring of intracranial pressure.

Forty-two epidural sensors for measuring intracranial pressure were implanted in 38 patients over the last four years. The sensor is a passive device consisting of an inductance and a pressure sensitive capacitance resonant at about 50 megahertz. The study involved 17 cases of hydrocephalus, nine of pseudotumor cerebri, and the remainder included cases of cranial trauma, brain tumors, and aneurysms. Four of the sensors failed in patients and were removed. Two of these had to be replaced to continue the pressure monitoring. The intracranial pressure is still being monitored in 22 patients, while 15 have been lost to follow-up for various reasons. Fourteen patients have been followed for about a year, and four for two years. The baseline drift rate in most sensors is between 1 and 2 mm H2O per day, with a few having greater rates of drift. Calibration errors were found in some of the sensors after implantation. These errors were corrected by direct measurement of the cerebral spinal fluid pressure via lumbar puncture. The sensors have proven to be a valuable adjunct in the management and diagnosis of neurosurgical patients by simplifying the intermittent and continuous recording of intracranial pressure. This was so despite the presence of calibration errors and a drift which necessitated an occasional lumbar puncture for making corrections.