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: