Question 4

Critically evaluate the risks versus benefits for the monitoring of Intra-Cranial Pressure in a patient with a closed head injury.

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College Answer

The benefits of monitoring ICP in closed head injury are still debated. Standard guidelines have been published but no prospective studies have demonstrated clear outcome benefits. The main purpose of monitoring the ICP is to allow the clinician to either guide therapy (add or remove) based on the ICP or CPP, or to alert the clinician to changes which may require further investigation. The lowest risk patients are least likely to benefit, so most criteria are based on a combination of patient characteristics and CT abnormalities.

Some risks (eg. haemorrhage) are related to insertion, and others (especially infection) are more likely with longer times in situ. Additional risks are associated with incorrect readings (abnormally high or low leading to the risk inappropriate/un-necessary interventions or investigations. Risks (and additional benefits) associated with ICP monitoring are largely dependent on the type of monitoring device.

Intraventricular catheters are more difficult to place, and are associated with a higher risk of haemorrhage during insertion, and subsequent infection (which increases in incidence with longer time in situ). These catheters have the additional advantage of being able to drain CSF (potentially therapeutic) and sample CSF (monitoring for infection and bleeding). Intraparenchymal devices (eg. fibreoptic Camino system) are easier to insert and are associated with a lower risk of haemorrhage and infection. Unfortunately, the transducer cannot be recalibrated, so reliability becomes a problem.

Less commonly used devices include: subarachnoid bolts which often clog with debris, and epidural catheters which are often inaccurate.

Discussion

The methods of ICP monitoring are discussed elsewhere.

Additionally, the chapter on the indications for ICP monitoring has a section outlining the risks of this practice.

In short:

Risks of ICP monitoring:

Risks of anaesthesia
Risks of craniotomy
Risks of haemorrhage
Risk of infection
Malposition and poor monitoring quality
Incorrect readings may stimulate incorrect management
EVDs may clog with debris; parenchymal monitors may "drift" from their zero calibration value
CPP-guided therapy may not improve outcomes

Benefit of ICP monitoring:

Prevention of secondary brain injury (however, may not improve outcomes)
Guide for hemodynamic therapy
Guide for timing of imaging and neurosurgical intervention
With EVD, the option to drain CSF contributes to ICP management
With EVD, sampling of the CSF is possible

In detail:

Advantages of Invasive Intracranial Pressure Monitoring
Prediction of outcome: average ICP in the first 48 hrs is a good independent predictor of both mortality and neuropsychological outcome There seems to be an improvement in mortality associated with the use of an ICP monitor in patients with severe traumatic brain injury, at least in some studies. Response to ICP-lowering therapies (or lack thereof) is a useful predictor of poor outcome. ICP monitoring did not appear to increase the length of stay or intensity of "brain-specific treatments" at least in one large 2012 study (Chestnut et al, NEJM) The BTF recommends ICP monitoring (i.e. the weight of international authority is behind this practice, whatever that means in court) An EVD is both a monitoring tool and a means of managing ICP. ICP monitoring is continuous, while clinical examination is intermittent; thus ICP monitoring can result in an earlier detection of new-onset intracranial hypertension from some new pathology, eg. a rebleed.

Disadvantages of Invasive Intracranial Pressure Monitoring
Routine ICP monitoring for all trauma patients may not influence mortality outcomes; or at least, there seems to be a lack of good evidence for a mortality-reducing role. Its role is therefore greatest in the management of severe TBI. Some studies suggest that it in fact does increase both length of stay and treatment intensitywithout any positive influence on outcome. The college, in their answer, quotes some sort of "BEST TRIPPS study". Presumably, that is the BEST:TRIP trial from 2012 ( Benchmark Evidence from South American Trials: Treatment of Intracranial Pressure). Indeed, it demonstrated an absence of mortality benefit. The exact conclusions were "for patients with severe traumatic brain injury, care focused on maintaining monitored intracranial pressure at 20 mm Hg or less was not shown to be superior to care based on imaging and clinical examination". ICP monitoring is associated with significant risk: Risks of anaesthesia Risks of craniotomy Risks of haemorrhage, especially in view of brain injury associated coagulopathy Risk of infection Malposition and poor monitoring quality Incorrect readings may stimulate incorrect management EVDs may clog with debris; parenchymal monitors may "drift" from their zero calibration value, leading to errors in decisinmaking.

References

Rosner, M. J., and D. P. Becker. "ICP monitoring: complications and associated factors." Clinical neurosurgery 23 (1975): 494-519.

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.

Smith, Martin. "Monitoring intracranial pressure in traumatic brain injury."Anesthesia & Analgesia 106.1 (2008): 240-248.

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