What are the essential components in assessing death by neurological criteria?
The Academy of the Medical Royal Colleges UK (AoMRC) code for the diagnosis of death by neurological criteria outlines three essential components:
1. Evidence of irreversible brain damage of known aetiology
2. Exclusion of reversible causes of coma and apnoea
3. Formal demonstration of coma, apnoea, and the absence of brainstem reflex activity
Which physiological criteria would exclude a patient from brainstem death testing?
Factor
Lower Limit
Upper Limits
Comments
Temperature Disturbance
34°c
-
Impaired consciousness can occur below 34°c
Biochemistry Disturbance
-
-
Derangements clearly the result of brainstem death (e.g. hyponatraemia of DI) may not require correction prior to testing
Sodium
115 mmol/l
160 mmol/l
-
Potassium
2 mmol/l
-
-
Magnesium
0.5 mmol/l
3.0 mmol/l
-
Phosphate
0.5 mmol/l
3.0 mmol/l
-
Glucose
3 mmol/l
20 mmol/l
-
Endocrine Disturbance
-
-
If there is any clinical reason to expect endocrine disturbances, hormonal assays should be undertaken.
Respiratory and Haemodynamic Disturbance
-
-
Requirement for cardiorespiratory stability is an important new prerequisite
pH
7.35
7.45
-
pCO2
-
6.0 kPa
-
pO2
10 kPa
-
-
MAP
60 mmHg
-
How are tests for brainstem reflex activity performed and what does each test check?
Test
Procedure
Confirmatory Response in Brainstem Death
Pupillary Reflex
A bright light is shone into each eye in turn. Direct and consensual reflexes should be sought
Pupils are fixed and do not respond or constrict to light
Corneal Reflex
Cornea is brushed lightly with a swab with care taken to avoid damage to the cornea.
No blinking elicited by stimulation
Caloric (Oculo-vestibular) Reflex
At least 50ml of ice cold water is instilled into the external auditory meatus over one minute. Head should be at 30 degrees to the horizontal plane. Clear access to the tympanic membrane must be confirmed by direct visualisation with and otoscope before testing
No eye movement during or following injection
Painful Stimulation
Painful stimulus is applied to the supra-orbital ridge (pons), and also to the limbs and trunk
No motor response in cranial nerve distribution elicited by stimulation
Gag Reflex
Posterior pharynx is stimulated with a spatula
No gag elicited by stimulation
Cough Reflex
Bronchial stimulation is performed by passing a suction catheter down the trachea to the carina
No cough elicited by stimulation
Which cranial nerves and brainstem levels are involved in the brainstem reflexes?
Test
Sensory Nerve
(Afferent Pathway)
Motor Nerve
(Efferent Pathway)
Brainstem Level
Pupillary Reflex
Optic nerve (II)
Oculomotor nerve (III)
Midbrain, pretectal olivary and Erdinger-Westphall nuclei
Corneal Reflex
Ophthalmic branch of trigeminal nerve (V)
Facial nerve (VII)
Pons, trigeminal and facial nuclei
Caloric (Oculo-vestibular) Reflex
Vestibulocochlear nerve (VIII)
Oculomotor nerve (III) & abducens nerve (VI)
Pons, nucleus vestibularus, nucleus abducens
Painful Stimulation (Brow)
Ophthalmic branch of trigeminal nerve (V)
Facial nerve (VII)
Pons, trigeminal and facial nuclei
Painful Stimulation (Limb)
Lateral spinothalamic tract
Facial nerve (VII)
Pons, trigeminal and facial nuclei
Gag Reflex
Glossopharyngeal nerve (IX)
Vagus nerve (X)
Medulla, nucleus tractus solitarius
Cough Reflex
Vagus nerve (X)
Vagus nerve (X)
Phrenic & intercostal nerves
Phrenic & intercostal nerves
Medulla, nucleus tractus solitarius