Diagnosis of Brain Death

The diagnostic algorithm has 3 sequential but interdependent steps:
1. Preconditions
2. Exclusions
3. Clinical Tests

1. Preconditions
i. Apnoeic coma
ii. Structural brain damage that is consistent with diagnosis of brain stem death
iii. The underlying disorder must be established
-evidende of sufficient intracranial pathology or a known cause of coma e.g. traumatic brain injury, intracerebral haemorrhage, hypoxic-ischaemic encephalopathy.

Exclusions: reversible causes of coma must be excluded

i. Alcohol and drug overdose
ii. Effects of therapeutic depressant drugs: take liver and renal function into consideration
iii. Residual action of NMB agents: ask whether Train of four stimulation has been performed to exclude neuromuscular paralysis.
iv. Hypothermia (T<35c): The patient is normothermic (T more than 35C)
v. Normotension: as a guide SBP more than 90 mmHg, MAP more than 60 mmHg in an adult
vi. without severe metabolic, electrolyte or endocrine derangement
vii. ability to adequately examine the brain stem reflexes
viii. ability to perform apnoea testing

Clinidal Tests:
- Canial nerve examination
i. Pupillary reflex -tests II and III
ii. Corneal reflex: tests V and VII
iii.Painful stimulus at 3 areas of V-tests V and VII
iv. vestibulo-ocular reflex : III, VI and VIII --llook in both ears to check that the canals are not occluded and the tympanic membranes are intact. Ask an assistant to hold the eyeslids open for you and then inject 20ml of ice cold water into each ear canal in turn. Movement of the eyes towards the side of the stimulus is an intact vestibulo-ocular response.
v. Gag and cough reflexes: IX and X -check under direct laryngoscopic vision. Check cough reflex using a tracheal suction catheter.

Note:
1. Apnoea tests
-The apnoea test confirms the absence of spontaneous respiratory effort despite PaCO2 at level above the threshold for respiration.
- may be difficult in cardioresp instability, spinal cord
-ventilate with 100% oxygen. Passively oxygenate during the test either using a Mapleson C circuit attached to the endotracheal tube. If starting PaCO2 is normal, allow it to rise to 60mmHg (pH 7.3) or 20mmHg higher than the patient's baseline if this is elevated (e.g. COPD). The rate of PaCO2 during apnoea is approximately 3mmHg/min
When assess the GCS, check response to voice before touching the patient. Response to pain should be tested by pressing on the supraorbital ridges (V), the temporomandibular joint (V) and a nail bed on each limb.
2. The oculocephalic reflex (doll's eye) is not part of the Australian brain death testing requirements.

Supplementary diagnostic techniques:
recommended tests by ANZICS -
1. Four vessels angiography -no blood flow above the carotid siphon in the anterior circulation and no blood flow above the foramen magnum in the posterior circulation
2. Radionuclide imaging - Tcc-99 HMPAO scan demonstrating absent intracranial perfusion
3. CT angiography: absent enhancement bilaterally of peripheral intracranial arteries and central veins at 60 seconds. There is less experience with this technique.

e.g.

1. Cranial nerves cannot be adequately tested-it must be possible to examine a least one ear and one eye

2. High Cervical cord injury is present or suspected. (preclued apnoea test)
3. Cardiorespiratory instability that precludes testing for apnoea. (severe hypoxic respiratory failure)
4. Possible drugs or metaolic effect on coma that cannot be excluded.