Ten-year follow-up on the performance of a telemetric intracranial pressure sensor

A permanently implanted epidural sensor has permitted long term telemetric intracranial pressure monitoring in selected neurosurgical patients. The sensor, consisting only of an inductance and a pressure-sensitive capacitance, has been implanted in 127 patients. Of these 127 patients, 13 have continued to have the sensor in place for 4 to 9 years (average, 6.8 +/- 0.44 years). The remaining patients were lost to follow-up or the sensor was removed. The sensor has been evaluated from the standpoint of accuracy, longevity, safety, and stability. Longevity was proven by successful monitoring over periods of years (in 1 patient, at least 9 years). The sensor has been a safe tool; the only morbidity has been two asymptomatic perisensor blood clots in 2 patients. There have been no infections in any of the 127 cases. The stability of the sensor was evaluated by measuring base line drift over time. This rate was 1.0 +/- 0.2 mm H2O/day. Causes of the drift and possible solutions are discussed, and the sensor is compared to other epidural telemetric monitoring systems.