What are the indications for intracranial pressure monitoring in traumatic brain injury? What are the limitations of intracranial pressure monitoring?
College Answer
All patients with severe head injury and moderate head injury whose progress can not be followed by serial neurological evaluation should be considered for ICP monitoring.
The Brain Trauma Foundation guidelines suggest ICP-monitoring should be considered in the following settings:
• Severe head injury (GCS 3-8) + abnormal CT scan
• Severe head injury (GCS 3-8) + normal CT scan if 2 of the following are presen):
o Age > 40
o BP < 90 mmHg
o Abnormal motor posturing
Individual intracranial pressure monitors have different limitations:
• Intraparenchymal monitors/subdural bolts: can not be calibrated, subject to “drift”, do not allow CSF drainage for control of ICP
• Require expertise and resource availability for placement
• Infection
No RCTs have demonstrated that ICP-guided therapy improves patient-centred outcomes.
Some observational studies have noted an association between ICP guided management and prolonged length of stay (Cramer, 2005) and worse outcome (Shafi, 2008).
Discussion
The indications listed in the college answer (including age, posturing etc) are from the old 3rd edition of the BTF guidelines. The enlightened 4th edition had reduced these recommendations to simply "anyone with an abnormal CT and GCS 3-8".
Limitations of intracranial pressure monitoring:
- No evidence that it impoves outcomes
- Monitors can become infected, inaccurate due to drift, or they can cause more intracranial bleeding.
- Neurosurgical expertise is required to insert these monitors
The college answer references papers by Cramer (2005) and Shafi (2008).
Presumably, they meant Olaf L. Cremer, who in 2005 was the first author of a retrospective cohort study which associated ICP-guided therapy with increased intensity of therapy and more prolonged mechanical ventilation, without a benefit to either survival or functional outcome. The examiners also mention Shahid Shafi's 2008 analysis of The National Trauma Data Bank (1994–2001) which found that ICP monitoring was associated with a 45% reduction in survival.
Greated detail is afforded by the summary of indications for intracranial pressure monitoring andmethods of intracranial pressure monitoring in the Required Reading section; to simplify revision the relevant grey boxes have been reproduced below.
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(Recommendations of The Brain Trauma Foundation, 4th edition)
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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 |
References
Chapter 43 (pp. 563) Cerebral protection by Victoria Heaviside and Michelle Hayes, and
Chapter 67 (pp. 765) Severe head injury by John A Myburgh.
Brain Trauma Organisation Guidelines for Management Traumatic Brain Injury.
Narayan, Raj K., et al. "Intracranial pressure: to monitor or not to monitor? A review of our experience with severe head injury." Journal of neurosurgery 56.5 (1982): 650-659.
Forsyth, Rob J., Susanne Wolny, and Beryl Rodrigues. "Routine intracranial pressure monitoring in acute coma." Cochrane Database Syst Rev 2 (2010).
Meythaler, Jay M., et al. "Current concepts: Diffuse axonal injury - associated traumatic brain injury." Archives of physical medicine and rehabilitation 82.10 (2001): 1461-1471.
Tasker, R. C., et al. "Monitoring in non-traumatic coma. Part I: Invasive intracranial measurements." Archives of disease in childhood 63.8 (1988): 888-894.
Cremer, Olaf L., et al. "Effect of intracranial pressure monitoring and targeted intensive care on functional outcome after severe head injury*." Critical care medicine 33.10 (2005): 2207-2213.
Shafi, Shahid, et al. "Intracranial pressure monitoring in brain-injured patients is associated with worsening of survival." Journal of Trauma and Acute Care Surgery 64.2 (2008): 335-340.
Lane, Peter L., et al. "Intracranial pressure monitoring and outcomes after traumatic brain injury." Canadian Journal of Surgery 43.6 (2000): 442.