A nurse is assisting with caloric testing of the oculovestibular reflex of an unconscious client. Cold water is injected into the left auditory canal. The client exhibits eye conjugate movements toward the left followed by a rapid nystagmus toward the right. The nurse understands that this indicates the client has:
A. A cerebral lesion
B. A temporal lesion
C. An intact brainstem
D. Brain death
Correct Answer: C. An intact brainstem
Caloric testing provides information about differentiating between cerebellar and brainstem lesions. After determining patency of the ear canal, cold or warm water is injected in the auditory canal. A normal response that indicates intact function of cranial nerves III, IV, and VIII is conjugate eye movements toward the side being irrigated, followed by rapid nystagmus to the opposite side. Absent or disconjugate eye movements indicate brainstem damage.
Option A: Caloric testing is clinically useful as a bedside test to isolate the peripheral vestibular system and rule out central etiology of vertigo. When there is a high suspicion for a peripheral lesion, bi-thermal caloric testing is typically performed. However, in cases in which there is a low pretest probability, it can be appropriate only to utilize mono thermic caloric testing and stop when the test is negative or in other words, responses are symmetric (therefore likely indicating a central process).
Option B: The advantage caloric testing has over other studies, such as the vestibular evoked myogenic potential and video head impulse test, is that it does not require head movement to be conducted, rendering better patient compliance in those patients whose symptoms worsen with movement, as well as in patients with limited cervical mobility.
Option D: Another indication for the use of this test is for brain stem testing in comatose patients. As described above, the reflex arc requires an intact brain stem, and therefore lack of nystagmus could indicate a brainstem lesion.
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