CALORIC TESTING

CALORIC TESTING – Definition, Purpose, Procedure, Interpretation and Preparation

The oculovestibular reflex or caloric test is a diagnostic examination providing information about the function of the vestibular portion of the eighth cranial nerve. It aids in the differential diagnosis of cerebellum and brainstem lesions

DEFINITION

Caloric test is performed by introducing either cold or hot water into the external auditory canal. A current then flows through the end lymphatic fluid, nystagmus is monitored in the both eyes (nystagmus is voluntary, rapid eyeball movement)

PURPOSE

This test checks the function of your acoustic nerve. This nerve is involved in hearing and balance. It also evaluates the function of brain areas involved in balance

Caloric stimulation is used to evaluate:

• Hearing loss caused by antibiotic use
• Vertigo (dizziness)
• Certain forms of anemia
• Psychological causes of vertigo
• Brain damage in comatose individuals

PROCEDURE

Caloric stimulation is performed by inserting first cold and then warm water into the ear canals. This is done one ear at a time. The water stimulates the nerves of the inner ear

Caloric stimulation usually follows these steps:

• Electrodes hooked up to a computer are placed around the eyes. These are used to measure eye movement during the test
• A small amount of cold water is inserted into the ear canal. This changes the temperature of the inner ear and causes rapid, side-to-side eye movements called nystagmus. The cold water causes the eyes to move away from the direction of the cold water and then slowly move back
• Warm water is then inserted into the ear. This time, the eyes should move toward the warm water and then slowly move back
• Eye movements are detected by the electrodes and recorded by the computer. Sometimes the person conducting the test visually observes the eye movements

INTERPRETATION

• When the vestibular eight cranial nerve is normal, stimulation of the auditory canal with hot water produce a rotatory nystagmus away from the side of the irrigated ear
• When cold water is used, the normal response is rotatory nystagmus toward the irrigated ear
• If pathology exits, nystagmus does not occur
• Sometimes, unpleasant symptoms such as vertigo, dizziness, nausea and vomiting occur
• Warn the client of possibility of these symptoms and give supportive nursing intervention
• Caloric tests are contraindicated in clients with perforated eardrums or with acute labyrinthine disease

Risk of the test: The test may cause some minor discomfort, especially when cold water is inserted. The test may cause brief feelings of vertigo, which can lead to nausea in some people. Although rare, it is possible for excessive water pressure to injure an eardrum. This is more likely if the eardrum has been damaged in the past. Your doctor should check your eardrum before the procedure. This test should not be used if it is damaged

PREPARATION

Some food and medications can affect your test results. For 24 hours before your test, you should avoid the following:

• Large, heavy meals
• Alcohol
• Caffeine
• Sedatives
• Allergy medications

Abnormal results: if your eye movements are abnormal, it may be a sign of acoustic nerve damage

Causes of abnormal result include:

• Trauma
• Blood clots
• Atherosclerosis of the blood supply to the ear
• Some poisons
• Blood vessel disorders
• Hemorrhage
• Ear tumors
• Rubella
• Congenital disorders

Ear nerve damage can also be caused by certain medications, including:

• Diuretics
• Antibiotics
• Antimalarial medications
• Salicylates

Results from this test can also be used to rule out or confirm diagnoses, including:

• Labyrinthitis
• Meniere’s disease
• Acoustic neuroma
• Benign positional vertigo