Two intracranial pressure (ICP) measurement devices represent the current standard of treatment: the intraparenchymal pressure monitor (or 'bolt') and the external ventricular drain (or 'ventriculostomy'). Various noninvasive methods, including transcranial doppler ultrasonography and MR imaging-based techniques, remain under investigation. External ventricular drains are small-diameter silicone tubes that are introduced into the lateral ventricle through a small burr hole in the skull (see Chapter 15 for insertion details). Blind passage of the catheter using external landmarks is usually adequate to cannulate the ventricle. The external ventricular drain is then attached with connectors to a closed, fluid-filled, sterile drainage system. The fluid column pressure is transduced to measure the ICP, and cerebrospinal fluid (CSF) may be drained to treat raised intracranial pressure. External ventricular drains are subject to a higher rate of infection than other ICP monitors and must be carefully leveled to the head of the patient to give accurate measurements. Prophylactic antibiotics are sometimes used in hopes of preventing infection. CSF specimens are collected every one to two days for infection surveillance.
Intraparenchymal pressure monitors utilize fiberoptic, strain-gauge or other technology to transduce pressure around the monitor tip into a graded electrical signal that is transmitted to a display and recording system outside the patient. Because the pressure transducer is actually within the head, these systems are not influenced by changes in the position of the patient or bed. These monitors are purely diagnostic and cannot be used to treat elevated ICP with CSF drainage. Some manufacturers have adapted fiberoptic monitors to extend through a ventricular catheter to allow accurate ICP measurement and CSF drainage.
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