Intracranial pressure monitoring

Even though ventricular fluid pressure is still regarded as the gold standard, most centres now use solid-state intraparenchymal monitors that are usually placed into the right (nondominant) frontal region through a small burrhole. While the ICP level is important (normal 10 mmHg, acceptable upper limit 25 mmHg), more significant is the CPP, calculated as the difference between mean arterial pressure and intracranial pressure, since CPP is the principal determinant of cerebral blood flow (CBF). The zero reference point for the ICP catheter and the arterial pressure transducer should be the same. There is a small risk of catheter displacement, haematoma, and drift of the zero baseline, but this has not been found to be clinically significant; if ICP readings are incompatible with other findings, however, it is worth considering removal and reinsertion of another catheter. Other methods of measurement include ventricular catheterisation - passing a catheter into the lateral ventricle through the non-dominant frontal lobe.58,60 There are small risks on insertion of such a catheter, and the risk of ventriculitis increases with time (particularly after 7 days), and with sampling CSF from the catheter. It can easily be checked against zero pressure, and can be used to withdraw CSF to reduce ICP. Future measurement of ICP may include a continuous estimate of intracranial compliance. Tissue perfusion is more likely to be related to compliance than pressure and critical volumetric compensatory exhaustion will be detected earlier with this measure, using, for example, the Spiegelberg device (Figure 2.2).

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Brain-Pressure Monitor

Figure 2.2 (a,b) Spiegelberg compliance monitoring device. Future measurement of ICP may include a continuous estimate of intracranial compliance. Tissue perfusion is more likely to be related to compliance than pressure, and critical volumetric compensatory exhaustion will be detected earlier with this measure. The Spiegelberg device is such a monitor and is currently available

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