Clinical testing for brain death is a favourite topic of the examiners. It frequently comes up in the SAQs and vivas. The most "examinable" aspects are the preconditions to testing, the precise sequence of testing, which cranial nerves are involved, and the expected findings of the apnoea test. Again, the ANZIC statement on Brain Death and Organ Donation is my primary resource for this summary. At the time of writing, the recent edition is Version 4 (2019)
Previous SAQs on this subject include the following:
Definition of brain death
- Unresponsive coma
- Absence of brain stem reflexes
- Absence of respiratory centre functions
- Clinical setting which suggests that these findings are IRREVERSIBLE.
- The demonstrated absence of intracranial blood flow
Preconditions for clinical brain death testing
The below preconditions are taken directly from the 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.
- A 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:
- Glucose <3 or > 25 mmol/L
- Sodium <125 or >160 mmol/L
- phosphate <0.5 mmol/L
- magnesium <0.5 mmol/L
- urea > 40 mmol/L
- "untreated severe hypothyroidism or severe hypoadrenalism"
- 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
Timing of brain death testing
- The clinical testing takes place at least 24 hrs after a cardiac arrest.
- Or, 24 hours after therapeutic hypothermia has been ceased (i.e. after the patient has rewarmed)
- Prior to 24 hrs, an arrested patients’ brain death can be determined by demonstration of absent cerebral blood flow.
- After 30 days of age, the same rules apply to children and to adults. In early neonates, younger than 30 days, 48 hours is the minimal period of observation (not 24).
- In premature newborns (before 36 weeks) begin death testing cannot be performed with certainty.
The process of clinical brain death testing
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
- There may be spinal reflexes; these will only be triggered by painful stimulus in the 4 limbs.
- The spinal reflexes will NOT be triggered by painful stimulus in the cranial nerve distribution.
Brain Stem Reflex Testing:
These are tested in sequence. All reflexes must be absent.
- Pupil Light Reflex: CN II, III
- Pupil constricts in response to light. Cataract surgery is no contraindication
- Corneal Reflex: CN V, VII
- Eye blinks in response to the cornea being touched. The cornea, not the sclera.
- Trigeminal Pain: CN V, VII
- Painful stimulus over the supraorbital nerve. There shouldn’t be any grimacing.
- Vestibulo-ocular reflex: CN III, IV, VI, VIII
- Examine the ear: auditory canal must not be blocked.
- Put the head at 30 degrees.
- Put ice-cold water into the ear
- Watch the eyes for 60 seconds: in brain death, they will remain midline.
- The “dolls eye test” is a sub-maximal stimulus of the same reflex
- Gag reflex: CN IX, X
- Poke the posterior pharynx, both sides.
- Cough reflex: CN X
- Stimulate the trachea with a soft suction catheter…this wont work in people with a high spinal cord injury, as the efferent limb is severed
Apnoea testing must be carried out only after the brainstem reflexes have been tested, and if any of them were found to be positive any further brain death testing cannot continue.
- Preoxygenate with 100% FiO2 for 5 minutes, and then turn off the ventilator.
- Continue supplying oxygen via a manual resuscitator with connected PEEP valve (they used to recommend a T-piece). Watch for absent breaths.
- After 10 minutes, take an ABG to demonstrate that the CO2 is rising and pH is falling (PaCO2 rises by 3mmHg every minute of apnoea).
- To qualify for brain death, "apnoea must persist in the presence of an adequate stimulus to spontaneous ventilation, i.e. an arterial PaCO₂ >60 mmHg (8 kPa) and an arterial pH <7.30"
To get through this without making the patient desperately hypoxic, the college permit mild hypoventilation (to a CO2 of 45). If the patient does become hypoxic, a couple of mandatory breaths are permitted to restore oxygenation, before carrying on with the process.
The ANZICS statement reports that there has never been a documented case of anybody who fulfilled the above brain death criteria, and the preconditions for brain death, who has ever recovered any brain function.
Findings compatible and incompatible with brain death
Observations compatible with brain death:
- Spinal reflexes in response to noxious stimulus:
- Extension-pronation movements of the upper limbs
- Nonspecific flexion of the lower limbs
- Undulating toe reflex
- Lazarus sign
- Deep tendon reflexes
- Plantar responses (flexor or extensor)
- Head turning
- Normal blood pressure in absence of vasopressors
- Absence of diabetes insipidus
Observations incompatible with brain death:
- Extensor posturing (decorticate)
- Flexor posturing (decerebrate)
- True extensor or flexor responses to painful stimuli
- Attempt at breathing, defined as any respiratory muscle activity that results in abdominal or chest excursions or activity of accessory respiratory muscles
For a more comprehensive overview, a good (ancient) article from the Acta Neurochirurgica describes what the authors have quaintly termed "Spinal Man", a species of human bereft of higher cortical function, which is a creature reliant purely on spinal reflexes.
Additionally, a more recent article discusses the various physiological responses to apnoea testing, including all the various cardiovascular derangements which occur.
a) - a seizure - rules out brain death
b) - a positive caloric reflex - is a brainstem reflex which is still working, and it rules out brain death
c) - arm flexion to ipsilateral painful stimulus - could be a spinal reflex, and does not rule out brain death.
d) - a Lazarus sign - does not rule out brain death
e) - a hypercapnea-associated catecholamine surge - can occur with zero cerebral input, and does not rule out brain death.