With respect to brain death and organ dbnation as specified in the ANZICS guidelines:
a) List the pre-conditions that would preclude the determination of brain death by clinical examination. (30% marks)
b) List the components of the clinical examination to determine brain death and where appropriate the cranial nerve(s) being tested. (40% marks)
c) If clinical testing has been precluded, what investigations can be used to demonstrate a lack of intracranial blood flow? (30% marks)
Conditions precluding clinical testing brain death
- Absence of diagnosis consistent with brain death
- Hypothermia (< 35 degrees)
- Hypotension (< 90 mmHg systolic or < 60 mmHg MAP in adult)
- Recent administration of sedative drugs
- Abnormalities of electrolyte, metabolic or endocrine function
- Recent administration of neuromuscular blocking agents or spinal cord injury
- Inability to adequately examine the brain stem reflexes (surgery to pupils/perforated ear drum)
- Inability to perform apnoea testing (acute lung injury)
- Minimum of 4 hour period of observation and mechanical ventilation during which patient has unresponsive coma
Clinical test Cranial Nerve
ii. Pupillary reflex II, III
iii. Corneal reflex V, VII
iv. Pain reflex in trigeminal nerve distribution V, VII
v. Vestibular ocular reflex III, IV, VI, VIII
vi. Gag reflex IX, X
vii. Cough reflex X
viii. Breathing effort with apnoea
- Four vessel intra-arterial angiography with digital substraction
- Radionucleotide imaging with Tc 99m HMPAO
- CT angiography – may be acceptable
Imaging techniques need to be done in association with exclusion of preconditions and assessment of those cranial nerves that can be assessed and results need to be reviewed by 2 appropriate clinicians excluding the clinician performing the test.
The below preconditions are taken directly from the ANZICS Statement.
- "Brain death cannot be determined without evidence of sufficient intracranial pathology". There must be an explanation for the coma which is consistent with the diagnosis of brain death.
- Minimum period of 4 hours in which the patient is observed to have unresponsive coma, unreactive pupils, absent cough/tracheal reflex and no spontaneous respiratory effort
- Exclusion of the effects of sedating drugs
- Absence of severe electrolyte, metabolic or endocrine disturbance
- Intact neuromuscular function
- Ability to adequately examine brainstem reflexes
- Ability to perform apnoea testing
Four hours of observation during which the patient remains in unresponsive coma
- GCS of 3
- Unresponsive pupils
- Absent cough reflex
- No spontaneous breathing efforts
Preconditions for apnoea testing
- Absence of concomitant high cervical cord injury
- Normoxia; satisfactory gas exchange
- Haemodynamic stability
- Absent brain stem reflexes
Testing for unresponsive coma
- Painful stimulus in cranial nerve distribution, eg. supraorbital nerve pressure
- Painful stimulus in all 4 limbs, eg. nailbed pressure
- There should be no response
Brain Stem Reflex Testing (these are tested in sequence; all reflexes must be absent)
- Pupil Light Reflex: CN II, III
- Corneal Reflex: CN V, VII
- Trigeminal Pain: CN V, VII
- Vestibulo-ocular reflex: CN II, IV, VI, VIII
- Gag reflex: CN IX, X
- Cough reflex: CN X
- Preoxygenate with 100% FiO2 for 5 minutes, and then turn off the ventilator.
- Continue supplying oxygen via T-piece or something similar. Watch for absent breaths.
- After 10 minutes, take an ABG to demonstrate that the CO2 is rising.
- To qualify for brain death, apnoea must persist despite adequate respiratory stimulus (PaCO2 60mmHg, or a rise by 20mmHg)
Investigations used to demonstrate a lack of intracranial blood flow are slightly different to those which might be used to demonstrate brain death, as the lattercategory may include such things as EEG (isoelectric EEG).
The imaging modalities are discussed in greater detail in the chapter on radiological testing for brain death.
In brief, the ANZICS-recommended modalities are:
- Tc-99 HMPAO SPECT scan
- DSA (Four-vessel Intra-Arterial Angiography)
Modalities which are not recommended as strongly include:
- CT angiography
- Transcranial doppler
The college says CT angio "may be acceptable", but in fact it is not. The argument againt CT angiography is the gated timing of the scan. Whereas DSA watches contrast wash in over time in a series of still images, the CT offers a momentary snapshot of that contrast in the vessels. One might argue that the CT was mis-timed, and the contrast did not yet have time to move into the brain (in this way, perfectly healthy people could be made to appear brain-dead by adjusting the timing of the scan). Obviously, when one is going to declare brain death, there needs to be no argument about the validity of the confirmatory test. The 2014 Cochrane review (Taylor et al) could not support the use of CTA.
Taylor, Tim, et al. "Computed tomography (CT) angiography for confirmation of the clinical diagnosis of brain death." The Cochrane Library (2014).