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Caloric Irrigation

Written by Michelle Petrak, Ph.D.

 

Table of contents

  1. What is caloric irrigation?
  2. Pre-test medications
  3. Pre-test examinations
  4. Tips before performing caloric irrigation
  5. How to instruct your patient
  6. Normal caloric results
  7. Normative values for caloric response parameters
  8. Abnormal caloric results
 

What is caloric irrigation?

The purpose of caloric irrigation is to identify the degree to which the vestibular system is responsive and to determine how symmetric the responses are, between left and right. It is a test of the lateral semicircular canals alone; it does not assess vertical canal function or otolithic function.

By using caloric irrigation, you are stimulating each end organ independently of the other to determine whether one end organ is weaker than the other (asymmetry) or whether neither end organ is providing enough vestibular information to the brain.

 

Pre-test medications

There is conflicting literature on whether patients should be asked to drop central nervous system suppressant medications for 48 hours before the test.

Part of this debate is that patients often do not understand which medications are allowed and which are not allowed.

A general rule of thumb is that the patient should stop taking medications that are prescribed for ‘dizziness’.

The patient can continue to take other medications, such as heart medications, blood pressure medications, and so forth.

 

Pre-test examinations

A thorough examination of the external ear canal and tympanic membrane is necessary before irrigation. Without, it is impossible to know whether the achieved test results are an accurate assessment of the vestibular system.

The three most important factors to consider are:

  1. The presence of cerumen
  2. The presence of a tympanic membrane perforation
  3. The shape of the ear canal

 

1. Cerumen

If excessive cerumen is present, it might prevent the stimulus from reaching the inner-most part of the ear canal.

This could prohibit a reliable test result.

Removal of even the smallest amounts of cerumen is beneficial to the testing process.

 

2. Tympanic membrane perforation

In the presence of a tympanic membrane perforation, you cannot do caloric stimulation by water.

You can only do stimulation by air briefly to determine whether or a not a vestibular response is present.

Yet, you cannot calculate accurate unilateral weakness and directional preponderance measures.

 

3. Shape of the ear canal

Examination of the shape and curvature of the ear canal is essential to reliable test results for two reasons:

(1) Because the irrigator tip is straight and ear canals rarely are, it is not uncommon for the insertion of the irrigator tip to cause slight discomfort to the patient.

(2) It is important for the stream of air/water from the irrigator to be directed near, but not directly on, the tympanic membrane to avoid injury to the patient.

 

Tips before performing caloric irrigation

Please consider the following before proceeding with the test.

 

1. Vision denial

It is necessary to perform caloric irrigation with the patient in a vision-denied state to disallow fixation suppression of the nystagmus response.

 

2. Alerting tasks

Alerting tasks are also necessary to discourage the patient from suppressing the nystagmus.

The most effective alerting tasks require the patient to use recall memory – i.e. “name a state that begins with the letter ____” ,“name a color that begins with ___”, “name a city in the state of ________”, etc.

 

3. Begin with warm irrigations

You should begin with warm irrigations (which provide an excitatory response).

This is because if the patient cannot tolerate bi-thermal irrigation, then you at least have enough information to provide a score for the Monothermal Warm Screening Test (MWST).

MWST is a screening test used mainly for patients who cannot tolerate bi-thermal testing. It is a percentage of asymmetry derived from only the warm caloric irrigation responses.

The mathematical formula for MWST is:

Mathematical formula for MWST. Reads (Right Warm minus Left Warm), divided by (Right Warm plus Left Warm), times a 100.

 

4. Wait 3-5 minutes between irrigations

You should wait between 3 and 5 minutes between irrigations, as the nystagmus from the previous test must be completely resolved before you perform the next irrigation.

Look at the eyes during the rest periods to watch the nystagmus dissipate.

Removal of the mask cover during these rest periods can be helpful to allow the patient to suppress any residual response.

 

5. Fixation period

A ‘fixation period’ of 10 seconds is recommended as a diagnostic tool during the recording of the caloric response (at approximately 90 seconds after the onset of irrigation).

The inability to suppress nystagmus when a fixation target is provided is considered a pathological sign of central vestibular pathology.

 

How to instruct your patient

For the sake of convenience, I have provided a full script below for inspiration:

“I am going to put warm and cool air/water into each ear. I will begin by putting warm air in the right/left ear. The air/water will sound loud and will feel warm, but it should not be painful. If you experience pain, please tell me immediately. The air/water will be in your ear for approximately 60 seconds (30 for water). After 60 (30) seconds, I will take the air/water out of your ear and I will begin to ask you questions. I need two things from you: to keep your eyes open AT ALL TIMES – even if you are feeling ‘like you are in motion’ - and focus on the questions that I am asking you to answer. Do you have any questions before we begin?”

It is also helpful to reassure the patient that the sensation of motion is to be expected and will not last very long.

 

Normal caloric results

A fully functional peripheral vestibular end organ will begin to respond to stimulation approximately 15‑30 seconds into the irrigation procedure and will reach its peak approximately 60-90 seconds from the beginning of the irrigation process (air stimulus is used in the examples shown below).

A rule of thumb is that warm air/water will produce nystagmus that beats toward the test ear and cool air/water will produce nystagmus that beats away from the test ear.

This is often referred to as Cold Opposite, Warm Same (COWS).

The nystagmus beats are represented by the dots plotted on the graph for each condition (Figure 1).

Caloric test summary screen, showing normal responses in both ears, for both warm and cool irrigations.

Figure 1: Caloric test showing normal response.

The yellow bar represents the area of maximum performance.

Each condition is giving a maximum Slow Phase Velocity (SPV) value and a Fixation Index value (FI).

All four SPV values are added and a total SPV value is also displayed.

The SPV values are used to calculate the overall weakness and to determine if any directional preponderance is present.

 

Normative values for caloric response parameters

The table below provides an overview of threshold values for caloric testing [1].

PARAMETER:

LABELED AS:

COMMON NORM:

Unilateral Weakness

UW%

<25%

Directional Preponderance

DP%

<30%

Fixation Suppression

FI%

<50%

Bilateral Weakness

Each ear total
>11 deg/sec

 

Hyperactivity

Each ear total
>140 deg/sec

 


Table 1: Threshold values for caloric testing.

 

How to calculate Unilateral Weakness

Using Jongkees formula, the mathematical formula for Unilateral Weakness is:

Mathematical formula for Unilateral Weakness. Reads left eye speed minus right eye speed, divided by total eye speed, times a 100.

How to calculate Directional Preponderance

Using Jongkees formula, the mathematical formula for Directional Preponderance is:

Mathematical formula for Directional Preponderance. Reads (Left Cool + Right Warm) minus (Right Cool + Left Warm), divided by total eye speed, times a 100.

 

Abnormal caloric results

Abnormal caloric test results can present in several ways:

(1) As an asymmetry between ears (unilateral weakness) (Figure 2).

(2) As directional preponderance, which numerically expresses how the amount of right-beating nystagmus compares with the amount of left-beating nystagmus (Figure 3).

(3) As a display of symmetrical, but weak, responses from both ears (bilateral weakness) (Figure 4).

Caloric test summary screen, showing a left unilateral weakness.

Figure 2: Caloric test showing a unilateral weakness.

 Caloric test summary screen, showing a right unilateral weakness, a directional preponderance, and an abnormal fixation value for left 44 degrees, shaded in yellow.

Figure 3: Caloric test showing a unilateral weakness, a directional preponderance, and an abnormal fixation value for left 44 degrees.

Caloric test summary screen, showing a bilateral weakness.

Figure 4: Caloric test showing a bilateral weakness. Please note that UW and DP will not be calculated when results present as a bilateral weakness.

 

Conclusion

Caloric irrigation is the most valuable tool available to the healthcare field with which to assess vestibular function.

It is the only test that allows for evaluation of each peripheral vestibular end organ independently of the other.

Caloric irrigation gives the healthcare professional an assessment of whether the peripheral vestibular end organs are functioning symmetrically and/or whether the peripheral vestibular end organs are providing the brain with enough sensory information.

 

Disclaimer

This is intended only as a guide; official diagnosis should be deferred to the patient’s physician.

 

References

[1] Jacobson, GP, and Shepard, NT. Balance Functional Assessment and Management, 2nd Ed. San Diego; Plural Publishing, 2015.

 

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