Question 27

Created on Tue, 05/12/2015 - 02:21
Last updated on Fri, 04/28/2017 - 17:23
Pass rate: 97%
Highest mark: 8.5

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A 59-year-old male is admitted to the ICU following a severe traumatic brain injury 
sedated, intubated and ventilated. 

a) List the arguments for and against intracranial pressure (ICP) monitoring in this 
patient. 

b) Explain the term "secondary brain injury" and list the steps to avoid this.

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College Answer

 

a) 
For: 
- This patient has about a 50 – 60% chance of developing raised ICP. 
- It is critical that CPP is maintained and to know the CPP need to know the ICP. 
- ICP is a strong predictor of outcome after severe TBI. 
- Several studies have shown substantial lowering of mortality after ICP monitoring and 
control was introduced. 
- Numerous studies have also shown that patients who respond to ICP-lowering therapies 
have a lower mortality compared to those who don't, allowing some prognostication. 
- Internationally accepted BTF Guidelines advise ICP monitoring in patients with severe 
TBI (GCS < 9) and an abnormal CT scan. 
- Doesn't lead to greater intensity of treatment or ICU LOS compared to no ICP 
- If EVD allows CSF drainage and analysis. 
- Early diagnosis of secondary surgically correctable lesion e.g.: delayed subdural 
haematoma.

Against: 
- Risks associated with brain injury associated coagulopathy. 
- Other risks – infection, false readings and risks of avoidable interventions (osmotherapy, 
falsely elevating CPP, deep sedation). 
- BEST TRIPPS study showing no difference in outcome. 
- May require transfer to OT for insertion. 

b) 
- Secondary injury occurs at any time after the primary injury, and thus should theoretically 
be preventable and is caused primarily by: 
o Hypoxia 
 Ensure a PaO2 > 80 and/or SpO2 > 92% 
o Hyper/hypocarbia 
 PaCO2 35 - 40mmHg 
o Hypotension 
 SBP > 90 mmHg and/MAP > 70 mmHg / CPP > 50 mmHg 
o Metabolic disturbance (Na, glucose, osmo) 
 Na+ of 140 – 150 mmol/L, glucose 6 – 10, Serum osmo 320 mOsm/L 
o Fever 
 Normothermia 
o Seizures 
 Phenytoin x 72hrs 
o Raised ICP 
 ICP lowering therapy (head up 30o, neck neutral alignment, sedation and 
paralysis, osmotherapy, drain CSF, surgical decompression) 
o Secondary surgical lesion (delayed subdural/parenchymal haemorhage) 
 Repeat CT, surgical therapy

 

Discussion

 

a) is a list of arguments for and against ICP monitoring. The debate about indications for intracranial pressure monitoring (strictly, whether there are any) is discussed in the Required Reading section.

To simplify revision, and because the author has succumbed to sloth, large greyish boxes have been lifted from that section and planted here with zero modification.

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

 

  • 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.

 

A precise definition of "secondary brain injury" is remarkably difficult to find, as occurs often with frequently used terminology of which everybody has some assumed intuitive understanding. Go on everyone, define "injury" in general. The college, in its model answer, does not define the term, but rather frames it in terms of problems and solutions.

Prevention of secondary brain injury - colloquially referred to as "neurprotective measures" - is discussed elsewhere, both as a brief summary and as a rambling dialogue. Salient points from the brief summary are lazily pasted below.

Goals of management, in summary:

Maintaining cerebral oxygen supply:

  • Normoxia: keep the PaO2 above 60 mmHg
  • Normotension: measure the MAP, and keep the systolic above 90mmHg
  • Intracranial Pressure monitoring: keep it under 20mmHg
  • Cerebral perfusion pressure: keep it 50-70mmHg
  • Cerebral oxygenation monitoring:keep the SjO2 >50%, and PbrO2 >55mmHg
  • Managing increased intracranial pressure for which there is a variety of strategies:
    • Draining the EVD ( about 20ml/hr, max)
    • Positioning the head straight
    • Removing the C-spine collar
    • Sedation :
      • Propofol sedation to decrease distress and thus decrease ICP
      • Barbiturate coma if other methods of lowering ICP have failed
      • Analgesia to prevent increased ICP in response to suctioning and routine care
    • Paralysis
    • Osmotherapy
    • Controversial measures
      • Decompressive craniectomy
      • Hypothermia
      • Dexamethasone

Decreasing cerebral oxygen demand:

  • Sedation
    • Propofol sedation to decrease distress and thus decrease ICP
    • Barbiturate coma if medical and surgical methods of lowering ICP have failed
  • Analgesia - opioid selection is irrelevant, but opiate boluses increase ICP
  • Seizure prophylaxis is infrequently indicated, and the course is 7 days only

Controversial measures:

  • Decompressive Craniectomy
  • Hypothermia
  •  

 

References

Our beloved Oh's Intensive Care manual has two excellent chapters to dedicate to this topic:

Chapter 43 (pp. 563) Cerebral protection by Victoria Heaviside and Michelle Hayes, and

Chapter 67 (pp. 765) Severe head injury by John A Myburgh.

However, the discerning reader will recognise this book as an antique, and look instead to the frequently updated Brain Trauma Organisation Guidelines for Management of 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).

Badri, Shide, et al. "Mortality and long-term functional outcome associated with intracranial pressure after traumatic brain injury." Intensive care medicine 38.11 (2012): 1800-1809.

Farahvar, Arash, et al. "Increased mortality in patients with severe traumatic brain injury treated without intracranial pressure monitoring: Clinical article."Journal of neurosurgery 117.4 (2012): 729-734.

Chesnut, Randall M., et al. "A trial of intracranial-pressure monitoring in traumatic brain injury." New England Journal of Medicine 367.26 (2012): 2471-2481.

Farahvar, Arash, et al. "Response to intracranial hypertension treatment as a predictor of death in patients with severe traumatic brain injury: Clinical article."Journal of neurosurgery 114.5 (2011): 1471-1478.

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.