(a) Outline the situations  in which clinical tests cannot be used to confirm brain death.

(b) List 2 adjunctive tests used in Australia and New Zealand  for the confirmation of brain death when clinical tests are unable to be performed.

(c) List other adjunctive tests which may have a role in the diagnosis of brain death.

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College Answer

a) Clinical tests cannot be used to confirm brain death in a number of situations, including:
•    No clear cause of coma
•    Possible drug or metabolic effect on coma
•    Cranial nerves cannot be adequately tested
•    Cervical vertebra or cord injury present
•    Cardiorespiratory instability precludes apnoea testing
•    In term infants and up to 1 year of age, on the assumption that the younger brain has a greater potential for recovery, a confirmatory test is usually conducted

b) The two adjunctive tests recognized in the ANZICS guidelines are 3 or 4 vessel angiogram, and nuclear medicine study capable of imaging posterior fossa blood flow, e.g. use of nuclear study with SPECT.

c) Additional tests which may play a role (but have various limitations) are electrophysiological tests (ie. evoked potentials, EEG), transcranial doppler ultrasound, and simpler nuclear medical perfusion scans. The use of Xe-CT and specific MR sequences have been described, but seem to hold no particular advantages. In the future, CT angiogram, or CT perfusion may play a role. Neither has obvious current advantages, but if sufficiently reliable, may be more widely available. Seventeen out of twenty-six candidates passed this question.

Discussion

This question closely resembles the following questions:

a) "Outline the situations  in which clinical tests cannot be used to confirm brain death." - This is really a question about the preconditions for brain death testing. Thus, clinical brain death testing canot be carried out if there is no obvious cause of the coma, when the patient is desperately hypoxic and hemodynamically unstable, and when you have no intact eyes or ears to test, etc etc.

Pre-conditions for brain death testing are discussed in several other fellowship questions:

In order to simplify revision, the list of reasons for not being able to perform clinical brain death testing is replicated here:

  • There is no obvious intracranial explanation for the coma
  • The patient is not normothermic
  • The patient is hemodynamically unstable
  • The effect of sedating drugs cannot be excluded
  • The effect of metabolic abnormalities cannot be excluded (eg. uremia, hypoglycaemia)
  • Neuromuscular function is not intact
  • Brainstem reflexes cannot be tested (eg. eyes and ears are not intact)
  • Apnoea testing cannot be performed (eg. severe hypoxia or high spinal cord injury)

b) " List 2 adjunctive tests used in Australia and New Zealand  for the confirmation of brain death when clinical tests are unable to be performed." - This is really a question about imaging modalities to confirm brain death. Four-vessel DSA and Tc-99m HMPAO are the better two, followed by CT angiography.

  • Question 12.2 from the second paper of 2010 discusses imaging modalities to assess the intracranial blood flow.

Additonal tests to confirm brain death - which are not gold standard material, but which are mentioned by the ANZICS Statement on Death and Organ Donation - include the following:

  • EEG (typical finding in brain death is an isoelectric EEG)
  • SSEP (somatosensory evoked potentials)
  • MRI
  • CT brain
  • Transcranial doppler

As diagnostic tools for brain death these leave much to be desired (owing to poor sensitivity or specificity), but as predictors of poor neurological outcome they have merit. In this context, these diagnostic modalities are discussed at great length in Question 4 from the second paper of 2013, "Describe the clinical signs and investigations available to predict poor neurological outcome in comatose survivors of cardiac arrest".

References

References

ANZICS Death and Organ Donation Committee, THE ANZICS STATEMENT ON DEATH AND ORGAN DONATION Edition 3.2 2013