eABR with Eclipse
1 Introduction: eABR overview.
1.1 What is eABR?
An electrical Auditory Brainstem Response (eABR) is a measurement of the ABR using an electrical stimulus. Instead of a traditional acoustic stimulus the cochlear implant (CI) or auditory brainstem implant (ABI) provides the stimuli that evokes the eABR.
1.2 Why eABR?
eABR testing may be performed for the following reasons:
- To verify adequate placement of the cochlear implant or auditory brainstem implant electrodes during surgery.
- To estimate electrical thresholds in infants, young children or other patients who cannot be assessed using behavioral techniques.
- To assist in mapping the cochlear implant or auditory brainstem implant device.
- To assess interactions between electrode channels.
2 System setup
Stimulation system and acquisition system are required to complete the basic system setup to proceed with eABR test.
2.1 Cochlear device used for stimulation
For stimulation you need the following materials:
- CI Software.
- CI programming device USB interface
- Processor connected to the CI programming device.
2.2 Eclipse device used for recording
- Eclipse 1.1 (with EP15 or EP25 license), hereafter referred to as ‘Eclipse’.
- Eclipse EP software.
- USB interface.
- Trigger cable for Eclipse 1.1 (see Figure 1).
- Preamplifier (manufactured from June,2019 or above serial number # ID114077).
- EPA3 cable collector.
- Three electrode cables.
3 Hardware set-up
- Ensure all the hardware components are arranged as guided in Figure 2.
- Ensure recording electrode cables are twisted to reduce the artefact from the stimulator.
- Ensure the cables used for stimulation are well separated from the recording cables in order to reduce the artefact.
3.1 Setting up CI programming software:
- Ensure the ‘CI Software’ is installed on the computer and available for use.
- Open the CI software, create a new patient profile if needed or access the existing patient profile1.
- Connect the processor.
- Proceed an Impedance Measurement for CI and make sure all electrodes are connected before testing eABR.
- Proceed with eABR test.
3.2 Setting up Eclipse:
- Turn on the Eclipse and double-Click on OtoAccess icon.
- Create a new client profile/access the existing one2.
- Click on the EP icon and the acquisition window appears
- Choose the eABR protocol for integrity tests and/or eABR recordings see Figure 3 and footnote No. 2).
- Now the Eclipse is ready to proceed with the eABR test.
4 Patient Preaparation
Patient preparation is very important to achieve the best test results. Optimally, the patient should be lying down, asleep and in a quiet environment. Minimally, the patient should be relaxed with their eyes closed during testing (Note: Usually eABR is not affected by anesthesia but consult with local physician).
Clean the patient skin with the abrasive gel (e.g. Nuprep.) to reduce the impedance. Impedance values at or below 3kΩ will produce cleaner recordings. Arrange electrode cables away from the cochlear implant connections to minimize interference.
Check the impedance (at or below 3kΩms) on the preamplifier (Note: If the impedances are higher than 5 kΩ, remove the surface electrodes, clean the skin and place new surface electrodes. Refer additional information manual for the detailed procedure of preparation of skin and impedance check).
4.1 Eelctrode placement:
Three (3) electrodes are connected to pre-amplifier as shown in the Figure 4.
- Positive: indicated by white color.
- Negative: indicated by yellow color.
- Ground: indicate by black color.
4.2 For eABR test:
- Positive: High forehead.
- Negative: Chin.
- Ground: Place on the side close to the implant.
Note: this is the recommended electrode montage position for eABR test (Figure 5)
An alternative method (see Figure 6) of electrode position, recording from the contralateral side.
- Positive: High forehead.
- Negative: Contralateral side.
- Ground: Low forehead.
5 Test Procedure:
5.1 eABR test:
In general, for eABR testing, few CI-electrodes are tested, from where a general electrical threshold is set across remaining CI-electrodes.
- From Eclipse application select the CI side (right/left), click on the intensity level corresponding to the CI electrode number, e.g. if the CI electrode to test is 4, then choose intensity 4dB to match electrode number and the recording label.
- Click on ‘Start’ button (now the eclipse is waiting for the Ci software to send the trigger signal to initiate the eABR recordings).
- Come back to CI software and set the test parameters for ‘eABR’ testing. Please refer to the CI manufacturer manual see footnote 2.
Note: when conducting post operation eABR, test amplitude and impulse duration should be defined at the comfortable level of the patient.
Now Click on Stimulation button (CI software).
The recording has started on Eclipse.
Open EP application on Eclipse.
When sufficient data has been collected (e.g. when residual noise has reached a level of 50nV), press ‘STOP’ button.
Repeat the steps from 1 to 7 of section 5.1 with different electrode number (in CI software, e.g: 4, 8, 12, 16) to cover all the 4 measurements required to complete the eABR test. The example of the eABR, in this case, electrode No. 4 was selected for eABR test and tested to threshold, is shown in the Figure 7.
- Electrode to test: 4 (recommended are 4,8,12,16).
- Stimulation rate: 26 Hz.
- Stimulation starting current level: 80CL (steps of 103).
- No of Stimulations to average: 4000.
5.2 Troubleshooting: (in case of recording problems in eABR test)
In case of too many rejections, change the EEG rejection level.
- Check the electrodes impedances of both the Eclipse surface electrodes and the CI electrodes.
- Be sure that recording and stimulation cables are well separated to minimize cross talk.
6 Result interpretation
6.1 How to interpret the eABR results?
The eABR test is to measure the electrical threshold of the individual CI electrode band. In optimum, a stimulus with the current level of 80 CL is used as starting point, from where it is decided to increase or decrease the amplitude/duration based on the presence of the response. The steps are typically increased/decreased in steps of 10.
In the example, electrical threshold of electrode no.4 was measured and typical result is shown in Figure 8.
Labels to each waveform can be added. In the example, current level was labeled, see Figure 9.
When comparing eABR to ABR, the following differences can be noted:
- eABR latency is approx. 2ms seconds earlier than ABR, hence, eABR Wave V is found typically around the 4ms.
- A minimal latency shift is seen in eABR with decreased stimuli duration.
Note: For more information about the Eclipse, please refer to the Eclipse User Manual.
1 Refer to CI manufacturer Medical User Manual for further details.
2 Refer to Eclipse User Manual for further details.
3 The steps are typically increased if there is no eABR response and decreased if there is an eaBR response.