The intraparenchymal catheter contains a membrane, distortion of which deflects a mirror and attenuates a fiberoptically transmitted beam of light. This attenuation, detected by a sensor, provides a measure of the pressure on the transducer membrane. The device can be placed into the parenchyma, ventricle or subdural space. Advantages include easy placement and less risk of ventriculitis. Disadvantages include drift in readings over time and inabilibty to recallibrate the device as well as inability to drain CSF throught the catheter.
All monitors have a risk of infection.
Infectious risk increases with duration of monitoring, particularly after the 5 th day. The site of monitoring is typically changed every 5-7 days. Intracranial waveforms resemble arterial waveforms. These appear to represent a tight brain and sudden increase in ICP, usually secondary to a fall in CPP and reflex increase in MAP until CPP is restored. An arterial line is indicated in all patients with an ICP monitor.