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
Brainstem Level
Pupillary Reflex
Midbrain, pretectal olivary and Erdinger-Westphall nuclei
Corneal Reflex
Pons, trigeminal and facial nuclei
Caloric (Oculo-vestibular) Reflex
Pons, nucleus vestibularus, nucleus abducens
Painful Stimulation (Brow)
Pons, trigeminal and facial nuclei
Painful Stimulation (Limb)
Pons, trigeminal and facial nuclei
Gag Reflex
Medulla, nucleus tractus solitarius
Cough Reflex
Medulla, nucleus tractus solitarius