Caloric Reflex (COWS): How does it work?

The Caloric Reflex Test is used to test the Vestibulo–ocular reflex. It is one of the tests used to assess for brain stem death.

HOW IT WORKS:

Cold (= or >30C) or warm water (= or > 44C) is flushed into the external auditory canal via a clean syringe. The difference in temperature between the water and your body generates convection signals in the endolymph of the ear mimicking head rotation. 

Mnemonic= COWS

The most common way to remember the normal response is COWS (used to remember the fast beating nystagmus response) in awake, normal subjects.

Irrigated with COLD water: Eyes deviate to ipsilateral (same-sided) ear and the nystagmus beats away to the OPPOSITE ear.

Irrigated with WARM water: Eyes deviate to contralateral (opposing-sided) ear and the nystagmus beats towards to the SAME ear.

Cold

Opposite

Warm

Same

An Excellent video that demonstrates the effect of cold water irrigation on an awake/ normal individual.

NOTE: In comatose patients, the nystagmus phase will not be present, only the conjugate eye deviation.

With brain stem damage the eyes remain mid line and the vestibular responses are abolished (or altered, depending on the severity of the lesion) SEE BELOW.

REFERENCES

1. Webb C. COWS caloric test. Ann Emerg Med. 1985 Sep;14(9):938.
2. Oculocephalic and Cold Caloric Reflexes (CN III, IV, VI and VIII). Derangedphysiology.com
3. Purves, Dale et al. NEUROSCIENCE: Third Edition. Sunderland, MA: Sinauer Associates, Inc., 2004. Print.