Protocol of Aided Cortical Auditory Evoked Potentials

Protocol of Aided Cortical Auditory Evoked Potentials
Protocol of Aided Cortical Auditory Evoked Potentials testing
Contents
1. Equipment required .................................................................................................... 1
2. Procedure ................................................................................................................... 1
2.1 Start Up ............................................................................................................. 1
2.2 Free-Field Calibration ..................................................................................... 2
2.3 Open/Create a Client File..................................................................................... 4
(1) Add a new client ............................................................................................... 4
(2) Search for an existing client ............................................................................. 5
(3) Edit client’s details ........................................................................................... 5
2.4 Conducting the Assessment ................................................................................. 6
(1) Specifying assessment settings......................................................................... 6
(2) Placement of electrodes .................................................................................... 7
(3) Impedance Check ............................................................................................. 7
(4) CAEP Acquisition ............................................................................................ 8
(5) Remove electrodes ......................................................................................... 10
3. Accessing the results ................................................................................................ 10
4. Printing assessment reports ...................................................................................... 11
5. Database backup ...................................................................................................... 12
Appendix 1: Electrode Application ............................................................................. 14
1. Equipment required
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HearLab
Cotton buds
Clean wipes
Disposable electrodes
Elastic bandage/headband
Nu-prep abrasive gel
Conductive EEG paste
Quiet Toys, books and DVD to entertain the child during testing
Tissue
Comfortable chair covered with towel
2. Procedure
2.1
Start Up
•
Switch on the power of HEARLab equipment
•
Ensure connections on the Stimulus Controller are correct.
Connect the speaker here
Connect the electrode
processor here
•
Connect the computer
USB cable here
Connect the control
microphone here
Double click the ACA icon on desktop
1
2.2
Free-Field Calibration
(1) Ensure that the control microphone is located at the subject position.
Calibrated free field
microphone
Free field
loudspeaker
e.g. 1m
(2) To open the “Free Field Calibration Wizard”, press keyboard
shortcuts Shift+Ctrl+Alt+K and click the “Free Field” button.
(3) Follow the on-screen steps to complete free-field calibration
Step 1: loudspeaker position
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Step 2: Distance of Loudspeaker
Step 3: Automatic calibration method
This distance should be
the same as the
measured distance
between microphone and
the approximate location
where a client’s head is
likely to be situated.
Step 4&5: loudspeaker setup
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For automatic free field calibration, a series of warble tones (from 125 Hz to 8 kHz in onethird octaves) will be presented through the loudspeaker. The signal will be recorded and
measured by the microphone, and the HearLab system will make automatic level adjustments
to achieve a flat frequency response.
•
You may pause or abort the calibration process at any time by pressing Pause or Abort button.
Step 6: Calibration
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(4) View and Save Calibration Results
Click View Results… to
view current calibration
results in a dialog window
which shows the
frequency response
obtained before and after
the calibration.
Click Finish to save the
calibration results and exit, or
Cancel to discard the
calibration results and exit.
Room’s last calibration
results for selected
loudspeaker position
Click to save last
calibration results as
an ASCII text file
Click to print last
calibration results
Click to return to free
field calibration
2.3 Open/Create a Client File
(1) Add a new client
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In the client screen, click the Add New Client icon on the toolbar
•
Fill in client details then click “OK” to save new client details to database. Ensure that
you fill in the DOB so that the appropriate P1 range for normal hearing listeners will be
displayed.
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(2) Search for an existing client
•
To work with an existing client, you may choose to either:
• Search the client by their details, OR
•
Find the client by listing all the clients in the database
- Name search is case sensitive.
- Wildcard character “%” can be use
e.g. enter Smi% and it will search
all clients’ surname starting with
List all clients
Double click to select a client
•
The selected client record, along with a list of the client’s previous assessment
records, will be displayed on the Client Screen.
(3) Edit client’s details
• Once you have selected an existing client, you can click Modify to edit client’s details
or Delete to delete the client’s record.
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2.4 Conducting the Assessment
(1) Specifying assessment settings
•
Open the New Assessment screen by clicking the icon on the main toolbar
•
Recommended settings:
Click the
appropriate
box
•
Click OK and a “New Run” dialog window will appear.
Select presentation level
Select stimuli
(maximum of 3,
minimum of 1).
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Select one stimulus only if the child’s attention span and test time are very
restricted. Prioritise stimuli according to frequency regions of interest, viz, /m/ for
low frequencies, /g/ for mid frequencies, and /t/, /s/ for high frequencies.
(2) Placement of electrodes
•
Prepare the electrode sites before attaching the disposable ECG
electrodes (see Appendix 1 for details).
•
Positions for the electrodes:
Electrode
Active
Reference
Ground
•
Placement
Vertex (Cz) ∗
Mastoid (M1)
Forehead (Fz)
Colour
Yellow
Blue
Black
Ensure the cords are plugged into the correct sockets with matching colours.
(3) Impedance Check
•
A good electrode contact is crucial before acquiring any cortical response. The
electrode impedance is checked, and if necessary redo the skin preparation to achieve
a recommended impedance under 5 kΩ at the Ref and the Cz electrodes.
The colours shown in each bar
for the 2 electrodes represent
how good the electrode
impedance is.
Good
Marginal
Satisfactory
•
Poor
Once the Impedance screen is displayed, impedance measurements will be performed
continuously at 1 second interval until you exit the Impedance screen.
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Cz is the midway of two ears and midway of the bridge of nose and the nape of neck. For infants, the
placement should be just behind the fontanel.
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Monitor the impedance of the Ref and Cz during assessment by clicking the
Impedance Check icon on the Assessment toolbar.
•
After the impedance check, click the “Acquisition” icon on the main toolbar to go to
the Acquisition screen.
(4) CAEP Acquisition
•
Once in the Acquisition screen, acquisition of cortical responses can be started,
paused, resumed, or terminated at any time during a run.
Controls
Stimulus
type & level
Averaged cortical
responses
MANOVA results of
detection of stimuli
Epochs
Latest p
values
Most recent obtained
cortical response
Residual
noise level
Ongoing brain activity
(EEG)
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• To start a test, click the Start button
. A dialog box will appear and you need to
type the file name and save the file.
• During acquisition, statistical analysis for determining the detection and differentiation of the
responses will be performed online.
Note that many factors may affect test results:
• Background noise may mask the stimulus and create “noise” in the electrical traces.
• Mobile phone signals may create electrical noise. Switch Mobile Phones Off.
• Other electrical interference e.g. fluorescent lighting
• Some medications such as those used to prevent seizures may affect the EEG.
• High muscle tone or sudden muscle movements such as experienced by some
children with cerebral palsy may make the EEG noisy and hence mask the response
• Awake status of the child - responses diminish when the child is drowsy or asleep.
• Impedance of electrode
You can monitor the number of accepted/rejected Epochs and the residual noise levels
by moving the cursor over the Residual Noise Level box.
• If the number of rejected Epochs is high, pause or stop the test.
• If the impedance is high, remove and replace electrodes or redo preparation.
• If the child is drowsy, revive the child before proceeding with further testing.
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• Click the Pause button
to pause acquisition for the current run e.g if you need
to access the Impedance Screen. You may also access the Result Screen or save the
results at this point.
• Click the Stop button
to manually terminate acquisition for the current run.
You may then view or save the results.
• Acquisition is automatically terminated once 200 accepted epochs for all selected
stimuli have been reached.
• A clear response should be: (a) p value is lower than 0.05; (b) Residual noise is green.
• After a test is terminated, you may choose to start another test by clicking New Run
icon on toolbar or start another assessment by clicking New Assessment.
• By clicking New Run, the results will be displayed on the same screen when you
view/print the results.
(5) Remove electrodes
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Once all testing is completed, remove and dispose of the electrodes
-
Use clean wipes to help remove the conductive paste.
3. Accessing the results
•
Results of the current assessment can be viewed on the results screen by clicking
the “View Results” button.
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Results of the previous assessment can be accessed under the Client Screen. All
the saved assessments of the selected client are displayed in the list. Double
click the assessment you wish to view.
•
Result Screen:
P level <0.05 will be
shown by a tick showing a
significant response
Test
conditions,
stimuli and
transducers
used
Averaged
cortical
responses
Click to view p values
instead of ticks/dashes
Click to
Add notes/
comments
4. Printing assessment reports
You may choose to look at the print preview of the assessment report before printing it out, or
you may print it directly.
Print report without preview
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•
Report preview:
Click Print
5. Database backup
It is important to regularly backup the database to prevent the loss of clinical records in the
case of mishap.
• To initiate database backup, go to Tools →Database Administration →
Backup Database
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A Browse For Folder dialog will be displayed:
Select the folder or make a new
folder for storing the backup data.
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Appendix 1: Electrode Application
Preparation of electrode sites
• Attaching the electrodes is potentially the most challenging part of the test procedure.
Approach the preparation confidently but not too forcefully. Smile, and talk to the
child reassuringly.
• Try not to physically “stand over” the child while doing skin preparation. Working
from behind the child may be a good option.
• Start the preparation in a position where the child is comfortable and not overly
restrained. For example, try starting while an older infant is playing on the floor, or
while a toddler is watching the DVD.
• Electrode sites are generally prepared by abrading with a cotton bud
and a medical gel intended for the purpose e.g. “Nuprep”. Rub
firmly and vigorously enough to cause a slight redness on the skin
surface, but not so hard that the child becomes obviously distressed
by the sensation.
• Wipe away any excess gel before applying the electrodes.
• Wherever possible have a trained distractor (in addition to the
parent), to interact with the child during electrode placement, as well
as during testing. Toys that involve some fine motor manipulation (e.g. block
stacking, button pressing) can help keep hands away from the electrode sites, and at
this stage toys that make a noise are suitable.
Optimising and maintaining electrode contact
•
Use a pea sized amount of electrode paste (e.g. the conductive EEG paste) under the
Vertex (Cz) electrode, even if disposable electrode, that already contains conductive
gel, is used. Avoid applying to the adhesive surrounds.
• A headband is very helpful in keeping the electrodes in place, particularly at the
vertex, but some children are less accepting of wearing a headband than others.
Giving older children a choice of colours or designs can be important to the child, and
sometimes also to the parent. Use fabrics that are easy to wash and dry after use.
• Once the electrodes are attached, try to drape the leads behind the child, avoiding
contact with the child’s face or neck. Try to keep the leads from becoming tangled in
bibs or collars.
• Loosely taping the leads to the back of the child’s clothing (using micropore tape or
hair clip) may be helpful. Make sure the leads are not taped too tightly that they are
pulled off by any head movement.
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