In medicine, the caloric reflex test (sometimes termed 'vestibular caloric stimulation') is a test of the vestibulo-ocular reflex that involves irrigating cold or warm water or air into the external auditory canal.

[edit] Utility

It is commonly used by audiologists and other trained professionals to validate a diagnosis of asymmetric function in the peripheral vestibular system. Calorics are usually a subtest of the electronystagmography (ENG) battery of tests. It is one of several tests which can be used to test for brain stem death.

One novel use of this test has been to provide temporary pain relief from phantom limb pains in amputees ^[1] and paraplegics.^[2]

[edit] Technique and results

Cold or warm water or air is irrigated into the external auditory canal, usually using a syringe. In patients with an intact brainstem:

• If the water is cold, relative to body temperature (30°C or below), the eyes turn toward the ipsilateral ear, with horizontal nystagmus (quick horizontal eye movements) to the contralateral ear.^[3][4]
• If the water is warm (44°C or above) the eyes turn toward the contralateral ear, with horizontal nystagmus to the ipsilateral ear.
• Absent reactive eye movement suggests vestibular weakness of the horizontal semicircular canal of the side being stimulated.

In comatose patients with cerebral damage, the fast phase of nystagmus will be absent as this is controlled by the cerebrum. As a result, using cold water irrigation will result in deviation of the eyes toward the ear being irrigated. If both phases are absent, this suggests the patient's brainstem reflexes are also damaged and carries a very poor prognosis^[5]

[edit] Mnemonic

One mnemonic used to remember the FAST direction of nystagmus is COWS.^[6]

COWS: Cold Opposite, Warm Same. Cold water = FAST phase of nystagmus to the side Opposite from the cold water filled ear, Warm water = FAST phase of nystagmus to the Same side as the warm water filled ear. Contralateral when cold is applied and ipsilateral when warm is applied

[edit] References