24A18: Exam Report
Compare and contrast the use of external ventricular drains with intraparenchymal fibreoptic pressure monitors to measure intracranial pressure.
38% of candidates passed this question.
This question required an accurate explanation of the mechanism of measurement for each device.
A head to head comparison of the differences and similarities in utility, accuracy, global versus regional measurements, calibration, drift and dampening should follow.
A comparison of potential complications was also expected.
20B07: Exam Report
Compare and contrast external ventricular drains and intraparenchymal fibreoptic pressure monitors.
22% of candidates passed this question.
This question is ideally suited to a tabular format, where candidates are expected to highlight the significant similarities and differences as well as why a certain monitor may be chosen in preference to another rather than compile two lists written next to each other. To score well in this question, a statement of what could be measured (ICP: global vs local), a description of the measurement principles, along with other measurement related information like calibration and sources of error was required. Also sought was information regarding anatomical placement (e.g., lateral ventricle for EVD) and method of placement.
Furthermore, a comparison with each other (e.g., higher infection/bleeding risk with EVD, greater risk of trauma due to size and insertion, expertise to insert, cost, therapeutic benefit, risk of blocking) was required for completion. Candidates who structured these elements into advantages and disadvantages were generally able to elucidate this information and score better.
K5i / 24A18 / 20B07: Compare and contrast external ventricular drains and intraparenchymal fibreoptic pressure monitors

EVD
Intraparenchymal Fiberoptic
Description
EVD
A flexible plastic catheter placed inside the lateral ventricles.
Can be either unilateral or bilateral placement
Gold standard for ICP monitoring
Intraparenchymal Fiberoptic
A think catheter inserted into parenchyma of the brain
Indication
EVD
Intraparenchymal Fiberoptic
Hydrocephalus
Post surgical/trauma intracranial haemorrhage
Meningitis
Location of Tip
EVD
Lateral ventricles
Intraparenchymal Fiberoptic
Below the dura – usually a few cms
Component
EVD
Plastic catheter
Wheatstone bridge
Fluid filled non compressible tubing
Pressurised fluid bag
Drainage bag
Monitor
Intraparenchymal Fiberoptic
Microsensor – intracranial
Fibre Optic cable
Monitor
Principle
EVD
Pressure is transmitted to a wheatstone bridge transducer via fluid filled non-compressible tubing
Intraparenchymal Fiberoptic
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
EVD
Able to be zero’d post insertion
Intraparenchymal Fiberoptic
Cannot be zero’d post insertion
Sources of Error
EVD
Migration of catheter
Blockage
Incorrect leveling to tragus
Damping and resonance
Intraparenchymal Fiberoptic
“Drift”
Increased inaccuracy >72hrs
Only measures ICP locally
Advantage
EVD
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
Intraparenchymal Fiberoptic
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
EVD
More skill required for insertion
More traumatic compared to bolt
Increased risk of ventriculitis
May be blocked
Complications: bleeding, malplacement, obstruction, migration, infection
Intraparenchymal Fiberoptic
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