Compare and contrast the use of external ventricular drains with intraparenchymal fibreoptic pressure monitors to measure intracranial pressure.
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.
This question closely resembles multiple questions from the Fellowship exam. Here, the answer from Question 8 from the first paper of 2010 is reproduced with zero modification:
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EVD |
Codman Microsensor |
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Gold standard of ICP monitoring |
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Pressure is transmitted to a Wheatsone bridge transducer via fluid-filled non-compressible tubing |
Piesoelectric strain gauge pressure sensor is intracranial; connected to the monitor via fiberoptic cable |
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Requires a certain expertise to place correctly. |
Requires less expertise to place (however, this should still be done by somebody with neurosurgical experience) |
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More traumatic owing to depth of insertion and diameter of catheter |
Less traumatic, because the catheter placement is not as deep, and the catheter tip is finer. The Codmans typically sits about 2cm below the cerebral surface. |
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CSF can be drained though the EVD |
CSF cannot be drained or sampled |
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The catheter can become blocked by clots or debris |
The catheter cannot block |
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Measures intraventricular pressure, |
Measures local parenchymal pressure |
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Can be re-zeroed to atmorpsheric pressure |
Cannot be re-zeroed after insertion; |
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Insertion is impossible if the ventricles are collapsed |
Does not rely on venticular placement, and thus is the only option in a patient with small collapsed ventricles |
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Dangerous in coagulopathy. Even when non-coagulopathic, the risk of haemorrhagic complications is around 5-7% on average |
Coagulopathy is only a relative contraindication; hemorrhagic complications are infrequent. One study puts the rate of bleeding at 1.1%. |
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Places the patient at risk of ventriculitis after 5 days. Bacterial colonisation rates range up to 27%, but studies vary in their definition of what a clinically significant infection actually is. |
Less likely to become infected; highly unlikely to cause ventriculitis, as it does not communicate with the entricles. |
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Cheap |
Expensive |
Brean, A., P. K. Eide, and Audun Stubhaug. "Comparison of intracranial pressure measured simultaneously within the brain parenchyma and cerebral ventricles." Journal of clinical monitoring and computing 20.6 (2006): 411-414.
Raboel, P. H., et al. "Intracranial pressure monitoring: invasive versus non-invasive methods—a review." Critical care research and practice 2012 (2012).
Lozier, Alan P., et al. "Ventriculostomy-related infections: a critical review of the literature." Neurosurgery 51.1 (2002): 170-182.
Saladino, Andrea, et al. "Malplacement of ventricular catheters by neurosurgeons: a single institution experience." Neurocritical care 10.2 (2009): 248-252.
Bekar, A., et al. "Risk factors and complications of intracranial pressure monitoring with a fiberoptic device." Journal of Clinical Neuroscience 16.2 (2009): 236-240.
Khan, S. H., et al. "Comparison of percutaneous ventriculostomies and intraparenchymal monitor: a retrospective evaluation of 156 patients."Intracranial Pressure and Neuromonitoring in Brain Injury. Springer Vienna, 1998. 50-52.