The primary disadvantage of the intraparenchymal monitor is that one can not drain fluid as with the ventriculostomy. In addition, there have been reports of drift in the baseline reading over a period of days. The transducer for these systems is at the tip of the wire and can be zeroed only prior to insertion. Kinking of the cable and dislocation of the screw have also been reported in several cases.
This type of monitor theoretically has less risk of hemorrhage than a ventriculostomy, as the ependymal lining of the ventricle is not disrupted. Also, it can continue to monitor pressure even when the ventricles are collapsed.
ICP monitoring when the ventricle can not be cannulated with a catheter or possibly when there is an increased risk of hemorrhage caused by coagulopathy.
The standard coronal twist drill hole is used and the dura is pierced with a #11 blade. A bolt, which has self-tapping threads, is then screwed into the skull until it is secure. A pediatric version can be used in smaller children. The fiberoptic cable is then coupled to the monitor and the system is zeroed while the tip is held in the air.
The wire is then passed through the bolt until it sticks into the brain parenchyma about 1 cm. The incision is closed securely around the bolt. If the ICP drifts or the fiberoptic system is damaged, then the entire system must be removed and changed.
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