Caloric Testing

Anatomy and Physiology

The semilunar canals are structures in the inner ear that play a vital role in maintaining balance and spatial orientation. There are 3 semilunar canals—horizontal, superior, and posterior. Each canal contains a fluid called endolymph and is responsible for detecting angular or rotational movements of the head. The semilunar canals dilate into a fluid-filled sac called the ampulla, which contains the sensory component of the vestibular system.[1]

Indications

Vertigo

Caloric testing is a bedside procedure that isolates the peripheral vestibular system and can eliminate central etiologies of vertigo.

Bithermal caloric testing is typically performed when a peripheral lesion is suspected. However, in cases with a low pretest probability of a peripheral lesion, monothermic caloric testing may be appropriate. If the results are negative, the test can be discontinued. A negative test reveals symmetric responses and is most consistent with a central etiology of vertigo.

Caloric testing offers several advantages compared to other testing methods, such as vestibular evoked myogenic potential and video head impulse test. This test does not require head movement and renders better compliance in patients whose symptoms worsen with movement and those with limited cervical mobility.[1][4]

Brainstem Testing

Caloric testing is also indicated for assessing brainstem function in comatose patients. As mentioned previously, the vestibulo-ocular reflex arc requires an intact brainstem; therefore, the absence of nystagmus may suggest a brainstem lesion.[5]

Hearing Loss

Caloric testing can evaluate cochlear function in conditions such as chronic hearing loss and Meniere's disease.[6]

Contraindications

Drugs that inhibit vestibular functions should be withheld 48 hours before caloric testing.[1]

The following medications are known to affect the vestibular system and may alter the results of caloric testing: 

• Antihistamines can cause drowsiness and dizziness.
• Tricyclic antidepressants may lead to balance problems.
• Antipsychotics can cause tardive dyskinesia, affecting the vestibular system.
• Narcotics can cause dizziness and drowsiness.
• Diuretics may result in dehydration, leading to dizziness.

Equipment

A water caloric irrigation system consisting of 2 baths of 250 mL distilled water, heated to 44 °C and 30 °C, respectively.[1]

Additional equipment:

• Catch basin (capacity up to 250 mL)
• Emesis basin
• Stopwatch
• Dry towel
• Optional: electro-oculography or video-oculography

Personnel

The procedure typically requires the primary clinician or technician to perform the caloric test and 1 or 2 assistants to manage essential tasks such as holding the catch basin, operating the stopwatch, and handling the dry towel.[1]

Preparation

The clinician should examine the external auditory canals using an otoscope to ensure no obstruction, infection, or cerumen impaction is present. The patient’s head should be elevated to a 30° angle to position the horizontal semicircular canal vertically, optimizing its stimulation during the test. The catch basin should be placed beneath the ear being irrigated.

If electro- or video-oculography is used, the electrodes should be attached, or goggles should be placed over the eyes. The patient should be instructed to perform an alerting exercise when the irrigation begins; for example, counting serial sevens out loud, naming animals, or listing words that start with the same letter.[1]

Technique or Treatment

The irrigation system delivers 250 mL of warm water solution to the ear canal over 25 to 30 seconds. An open system allows the delivered water to drain freely from the external auditory canal and collect in the basin. The nystagmus beats begin approximately 30 seconds after the onset of the water delivery and build in intensity over the ensuing 30 to 45 seconds. The alerting exercise performed by the patient prevents suppression of nystagmus. After waiting 5 minutes, the process should be repeated on the other ear. The process should be repeated using cool water if indicated.[1]

If there is no response to either warm or cool irrigation, or if a bithermic irrigation system is unavailable, ice water irrigation can be considered. The patient should be instructed to lie in a semirecumbent position with the ear of concern facing upward. Approximately 2 mL of ice water is injected into the external auditory canal using a syringe. The patient should hold their position for 30 seconds and then turn their head to the midline. Nystagmus should be observed while the patient performs alerting tasks. This testing method has higher sensitivity and specificity than warm air or water, although it may not be as well tolerated.[7]

The acronym WARMCOLD helps healthcare providers remember the correct order of steps during caloric testing, ensuring accurate testing and reliable results that can aid in diagnosing vestibular disorders.

The steps for conducting caloric testing are as follows:

• W - Warm: Introducing warm air or water into the external auditory canal causes the endolymph in the semilunar canals to move, stimulating the hair cells and inducing reflexive nystagmus.

• A - Alternate: Alternating the stimulus to cold air or water in the external auditory canal causes the endolymph in the semilunar canals to move in the opposite direction, stimulating the hair cells and producing nystagmus.

• R - Return: Returning to a warm stimulus, either air or water, after the cold stimulus causes the endolymph in the semilunar canals to move in the same direction as the first warm stimulus, stimulating the hair cells and causing nystagmus.

• M - Measure: Measure the patient's eye movements and compare their results to typical values to evaluate the function of the inner ear and the vestibular system.

• C - Compare: Compare the eye movement after performing caloric testing in both ears to check for an asymmetrical response.

• O - Observe: Observe any spontaneous or positional nystagmus that may indicate a central lesion.

• L - Look: Look for any other symptoms, such as vertigo, dizziness, nausea, or tinnitus, that the patient may be experiencing.

• D - Document: Document all the observations and measurements made during the test and compare them with typical values to evaluate the function of the inner ear and the vestibular system.[2]

The mnemonic COWS (cold, opposite, warm, same) helps clinicians remember the pattern of nystagmus responses.

Complications

The adverse effects of caloric testing are generally mild and temporary. Some patients may experience a feeling of fullness or pressure in the ear and a slight increase in dizziness or vertigo. These symptoms typically subside within a few minutes of test completion. In rare cases, some patients experience more severe adverse effects such as vertigo, nausea, or vomiting. Long-term sequelae are not commonly associated with caloric testing.[1]

Clinical Significance

Caloric testing is a valuable diagnostic tool for differentiating between central and peripheral vestibular pathologies by assessing the function of the horizontal semicircular canals and the vestibulo-ocular reflex (VOR).

This test helps differentiate central and peripheral etiologies of dizziness. Ideally, a warm testing medium is used to assess vestibular function in patients with a low pretest probability of a peripheral process; monothermic testing reportedly has a wide range of sensitivity (0.54-1.00) for a unilateral vestibulopathy and, therefore, has limited use when the pretest probability is intermediate.[8] Thus, bithermic testing should be used for patients with a high pretest likelihood of a peripheral etiology.

Although warm water is a more commonly used testing medium, caloric testing with warm air has also been reported to be 87% sensitive with a negative predictive value of 90% when assessing for unilateral vestibular weakness when a cutoff of 25% inter-ear difference is used.[9] Despite this, a cold medium produces a more drastic response in the measured slow-phase nystagmus, making it easier for the practitioner to identify. Therefore, it is a more specific test for confirming a peripheral lesion.[10] For patients in whom air or water stimulation is contraindicated, such as those with chronic suppurative otitis media or tympanic membrane perforations, near-infrared radiation is an equally efficacious alternative method for caloric testing.[11]

Normal Results

Caloric stimulation (using warm or cold water or air) induces a predictable nystagmus response in individuals with normal vestibular function. The average slow-phase velocity (SPV) of caloric nystagmus in a normal vestibular system is approximately 17.4°/s.[12] The response should be symmetric between both ears, with minimal directional preponderance.

The Cold Opposite Warm Same (COWS) mnemonic helps clinicians remember the expected direction of nystagmus during caloric testing. Nystagmus is divided into the slow phase (pursuit) and the fast phase (saccade). When cold water or air is used to irrigate the ear, the fast phase should beat to the opposite side. Conversely, when warm water or air is used, the fast phase should beat to the same side.  

Peripheral pathology

In peripheral vestibular lesions, such as vestibular neuritis or Meniere's disease, the caloric response is typically diminished on the affected side. This results in a decreased slow-phase velocity (SPV) of nystagmus. For example, in Meniere's disease, caloric testing often shows unilateral weakness with a significant reduction in SPV on the affected side. The COWS mnemonic still applies, but the response may be weaker or absent on the affected side.[12]

Central pathology

Central vestibular dysfunctions, such as brainstem or cerebellar lesions, can present with atypical caloric responses. These may include increased SPV and spontaneous nystagmus, suggesting impaired central inhibitory mechanisms. Additionally, central lesions may result in abnormal fixation suppression, where the nystagmic response is not adequately suppressed by visual fixation, leading to a low fixation index. In some cases, central pathology can cause perverted nystagmus or premature reversal of nystagmus direction, which deviates from the expected COWS pattern.[12] 

In summary, the COWS mnemonic is a helpful guide for interpreting caloric test results, but clinicians must consider the context of peripheral versus central pathology. Peripheral lesions typically show reduced responses on the affected side, while central lesions may present with atypical or exaggerated responses.  

Limitations

Caloric testing, often considered the gold standard for detecting unilateral vestibular hypofunction, has limitations in acute settings. It only stimulates the horizontal semicircular canal, is time-consuming, and can be uncomfortable for patients. Recent data suggest that the video head impulse test (vHIT) is more accurate in distinguishing between stroke and vestibular neuritis and may offer a more feasible option for evaluating patients with acute dizziness. [13]

Enhancing Healthcare Team Outcomes

Caloric testing to assess vestibular dysfunction is typically performed by the practitioner as a bedside test, though additional assistance from nursing staff may be needed to ensure proper execution. In addition, if electro-oculography or video-oculography is used, expertise and specialized training in handling this equipment are essential, and input from a trained audiologist may be required.

Caloric testing with warm air is suitable for patients with chronic suppurative otitis media and perforations of the tympanic membrane. This method requires less preparation and fewer personnel, potentially reducing complications compared to testing with water.[4]