Canonical Question

Neuro Measurement – ICP

Master answer

	EVD	Intraparenchymal fiberoptic
Description	• A flexible plastic catheter placed inside the lateral ventricles. • Can be either unilateral or bilateral placement • Gold standard for ICP monitoring	A think catheter inserted into parenchyma of the brain
Indication	• Hydrocephalus • Post surgical/trauma intracranial haemorrhage • Meningitis	same
Location of tip	Lateral ventricles	Below the dura – usually a few cms
Component	• Plastic catheter • Wheatstone bridge • Fluid filled non-compressible tubing • Pressurized fluid bag • Drainage bag • Monitor	• Microsensor – intracranial • Fiber Optic cable • Monitor
Principle	Pressure is transmitted to a Wheatstone bridge transducer via fluid filled non-compressible tubing	Changes in ICP move a displaceable mirror at the tip of the sensor to alter the intensity of light reflected back along the fiber optic cable
calibration	Able to be zero’d post insertion	Cannot be zero’d post insertion
Sources of error	• Migration of catheter • Blockage • Incorrect leveling to tragus • Damping and resonance	• “Drift” • Increased inaccuracy >72hrs • Only measures ICP locally
Advantage	• Has diagnostic values (CSF sampling, elevated ICP, new haemorrhage) as well as therapeutic values (drainage of excessive CSF, administration of medication) • Global measurement of ICP • Can be converted to cerebral shunt – long term treatment • Cheap	• Less expertise required for insertion • Less traumatic • Able to be placed in patients with small collapsed ventricles • Less infection risk • No risk of blockage
Disadvantage	• More skill required for insertion • More traumatic compared to bolt • Increased risk of ventriculitis • May be blocked • Complications: bleeding, malplacement, obstruction, migration, infection	• Only local ICP is measured • No therapeutic value: CSF cannot be drained • Less accurate due to drift and unable to be calibrated post insertion • Expensive

Guo 2021

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