This protocol was approved by the local Ethics Committee in accordance with the Helsinki Declaration (Ruhr-University Bochum: Reg.-No.: 21-7373; Medical University Innsbruck Reg.-No.: 1060/2021). Informed consent was obtained from all participants.
1. Preparation for the surgery
<ol>
	<li>Make sure to obtain audiological testing reports, including pure-tone audiometry, objective testing (e.g., brainstem evoked response audiometry, speech testing), and vestibular diagnostics ...

Real-Time Telemetric Impedance Measurements During Cochlear Implantation

<ol>
	<li>Dalbert, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hearing+preservation+after+cochlear+implantation+may+improve+long-term+word+perception+in+the+electric-only+condition.">Hearing preservation after cochlear implantation may improve long-term word perception in the electric-only condition.</a> Otology &amp; Neurotology. 37 (9), 1314-1319 (2016).</li><li>Thompson, N. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrode+array+type+and+its+impact+on+impedance+fluctuations+and+loss+of+residual+hearing+in+cochlear+implantation.">Electrode array type and its impact on impedance fluctuations and loss of residual hearing in cochlear implantation.</a> Otology &amp; Neurotology. 41 (2), 186-191 (2020).</li><li>Aebischer, P., Meyer, S., Caversaccio, M., Wimmer, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intraoperative+impedance-based+estimation+of+cochlear+implant+electrode+array+insertion+depth.">Intraoperative impedance-based estimation of cochlear implant electrode array insertion depth.</a> IEEE Transactions on Biomedical Engineering. 68 (2), 545-555 (2021).</li><li>Choi, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrode+impedance+fluctuations+as+a+biomarker+for+inner+ear+pathology+after+cochlear+implantation.">Electrode impedance fluctuations as a biomarker for inner ear pathology after cochlear implantation.</a> Otology &amp; Neurotology. 38 (10), 1433-1439 (2017).</li><li>Shaul, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+impedance+as+a+biomarker+for+inner+ear+pathology+following+lateral+wall+and+peri-modiolar+cochlear+implantation.">Electrical impedance as a biomarker for inner ear pathology following lateral wall and peri-modiolar cochlear implantation.</a> Otology &amp; Neurotology. 40 (5), e518-e526 (2019).</li><li>Bester, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Four-point+impedance+as+a+biomarker+for+bleeding+during+cochlear+implantation.">Four-point impedance as a biomarker for bleeding during cochlear implantation.</a> Scientific Reports. 10 (1), 2777 (2020).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> MED-EL. , (2023).</li><li>Lenarz, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cochlear+implant+-+state+of+the+art.">Cochlear implant - state of the art.</a> GMS Current Topics in Otorhinolaryngology, Head and Neck Surgery. 16, Doc04 (2018).</li><li>Gaw&#281;cki, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Robot-assisted+electrode+insertion+in+cochlear+implantation+controlled+by+intraoperative+electrocochleography-A+pilot+study.">Robot-assisted electrode insertion in cochlear implantation controlled by intraoperative electrocochleography-A pilot study.</a> Journal of Clinical Medicine. 11 (23), 7045 (2022).</li><li>Jia, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+and+cellular+mechanisms+of+loss+of+residual+hearing+after+cochlear+implantation.">Molecular and cellular mechanisms of loss of residual hearing after cochlear implantation.</a> Annals of Otology, Rhinology, and Laryngology. 122 (1), 33-39 (2013).</li><li>Eshraghi, A. A., Van de Water, T. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cochlear+implantation+trauma+and+noise-induced+hearing+loss:+Apoptosis+and+therapeutic+strategies.">Cochlear implantation trauma and noise-induced hearing loss: Apoptosis and therapeutic strategies.</a> The Anatomical Record. Part A, Discoveries in Molecular, Cellular, and Evolutionary Biology. 288 (4), 473-481 (2006).</li><li>Van De Water, T. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Caspases,+the+enemy+within,+and+their+role+in+oxidative+stress-induced+apoptosis+of+inner+ear+sensory+cells.">Caspases, the enemy within, and their role in oxidative stress-induced apoptosis of inner ear sensory cells.</a> Otology &amp; Neurotology. 25 (4), 627-632 (2004).</li><li>Roland, P. S., Wright, C. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surgical+aspects+of+cochlear+implantation:+mechanisms+of+insertional+trauma.">Surgical aspects of cochlear implantation: mechanisms of insertional trauma.</a> Advances in Oto-Rhino-Laryngology. 64, 11-30 (2006).</li><li>Tien, H. -. C., Linthicum, F. H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histopathologic+changes+in+the+vestibule+after+cochlear+implantation.">Histopathologic changes in the vestibule after cochlear implantation.</a> Otolaryngology-- Head and Neck Surgery. 127 (4), 260-264 (2002).</li><li>Lenarz, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Relationship+between+intraoperative+electrocochleography+and+hearing+preservation.">Relationship between intraoperative electrocochleography and hearing preservation.</a> Otology &amp; Neurotology. 43 (1), e72-e78 (2022).</li><li>Bester, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrocochleography+triggered+intervention+successfully+preserves+residual+hearing+during+cochlear+implantation:+Results+of+a+randomised+clinical+trial.">Electrocochleography triggered intervention successfully preserves residual hearing during cochlear implantation: Results of a randomised clinical trial.</a> Hearing Research. 426, 108353 (2022).</li><li>O'Leary, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intraoperative+observational+real-time+electrocochleography+as+a+predictor+of+hearing+loss+after+cochlear+implantation:+3+and+12+month+outcomes.">Intraoperative observational real-time electrocochleography as a predictor of hearing loss after cochlear implantation: 3 and 12 month outcomes.</a> Otology &amp; Neurotology. 41 (9), 1222-1229 (2020).</li><li>Dong, Y., Briaire, J. J., Siebrecht, M., Stronks, H. C., Frijns, J. H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+translocation+of+cochlear+implant+electrode+arrays+by+intracochlear+impedance+measurements.">Detection of translocation of cochlear implant electrode arrays by intracochlear impedance measurements.</a> Ear and Hearing. 42 (5), 1397-1404 (2021).</li><li>Giardina, C. K., Krause, E. S., Koka, K., Fitzpatrick, D. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Impedance+measures+during+in+vitro+cochlear+implantation+predict+array+positioning.">Impedance measures during in vitro cochlear implantation predict array positioning.</a> IEEE Transactions on Biomedical Engineering. 65 (2), 327-335 (2018).</li><li>Sijgers, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Predicting+cochlear+implant+electrode+placement+using+monopolar,+three-point+and+four-point+impedance+measurements.">Predicting cochlear implant electrode placement using monopolar, three-point and four-point impedance measurements.</a> IEEE Transactions on Biomedical Engineering. 69 (8), 2533-2544 (2022).</li><li>Salkim, E., Zamani, M., Jiang, D., Saeed, S. R., Demosthenous, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insertion+guidance+based+on+impedance+measurements+of+a+cochlear+electrode+array.">Insertion guidance based on impedance measurements of a cochlear electrode array.</a> Frontiers in Computational Neuroscience. 16, 862126 (2022).</li></ol>

Repeated impedance measurements are a promising approach to gain real-time feedback from the cochlea during the insertion process. They indicate which electrode contacts are positioned inside the perilymph or not. With the here presented novel method for flexible lateral wall electrodes (MED-EL, Innsbruck, Austria)7, impedances may be measured in real-time during cochlear implantation utilizing the inserting electrode array.&#160;However, for reliable measurements, a standardized procedure is cruc...

Preserving residual hearing is an increasing topic of interest in cochlear implantation (CI) surgery, and the indication has changed towards candidates with functional residual hearing. Thus, measurements that may objectify the position of the electrode array and the resulting potential intracochlear damage during surgery are becoming increasingly important. CI-users with successfully preserved hearing have been shown to have superior hearing performance with the implant after surgery, even when stimulated electrically-only1. Some of them may additionally benefit from acoustic stimulation (electro-acoustic stimulation; EAS). Perioperative hearing loss is assumed to result from traumatic insertion. To improve insights into these intraoperative changes and to establish monitoring algorithms, objective measures, and biomarkers are needed. In this context, impedance telemetry may be of interest2,3. Increased impedances have been shown to be associated with hearing loss or vertigo4,5. Further evidence associates blood inclusions during the insertion of the electrode array6. Nevertheless, further investigation is necessary to explore to what extent impedances may be associated with surgical trauma and postoperative performance. For this purpose, repeated intraoperative impedance measurements are a promising approach. On the other hand, impedances deliver additional information about the electrode&#39;s position. High impedances indicate poor conductivity and thus indicate a contact position outside the cochlea, whereas low impedances (impedance drops) may indicate already inserted contacts. Thus, impedances may be used as an objective feedback mechanism for the status of the electrode array insertion. In this video, we present our setup and first experiences with this novel approach of repeated impedance measurements using flexible lateral wall electrodes from the cochlear implant manufacturer MED-EL (Innsbruck, Austria)7.
A study software designed for research purposes is used to perform repeated impedance measurements. In this study, the software is verified according to the MED-EL internal procedures for research-use-only devices. During surgery, only the most recent impedance telemetry data is shown. Figure 1 shows the electronic measurement setup. The Insertion Monitoring (IM) software has buttons to mark the number of electrode contacts currently inserted (red/green highlighting). After starting, the software measures impedances repeatedly in cycles. The IM software shows a table of the measured impedance results and impedances across time in 12 plots. Furthermore, it shows warnings in case of connection problems. A video recording Software (Open Broadcaster Software [OBS]) is used to record (i) the video of electrode insertion (microscope attached, e.g., via HDMI), (ii) a video of the IM software user interface, including all user interactions and (iii) sound. An audio editor software (Audacity) is used to regularly play a sound during the insertion of the electrode array to facilitate a slow insertion.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Audacity</td>
			<td>Open source</td>
			<td>https://www.audacityteam.org/</td>
			<td>Audio editor software</td>
		</tr>
		<tr>
			<td>Coil cable</td>
			<td>Any appropriate brand</td>
			<td></td>
			<td>Implant interface</td>
		</tr>
		<tr>
			<td>Computer</td>
			<td>Any appropriate brand</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Electrode array</td>
			<td>MED-EL</td>
			<td>https://s3.medel.com/pdf/21617.pdf</td>
			<td>Standard, FlexSoft, Flex28</td>
		</tr>
		<tr>
			<td>IM Software</td>
			<td>MED-EL</td>
			<td>https://www.medel.com/</td>
			<td></td>
		</tr>
		<tr>
			<td>Maestro</td>
			<td>MED-EL</td>
			<td>https://www.medel.com/</td>
			<td></td>
		</tr>
		<tr>
			<td>MAX Interface USB</td>
			<td>Any appropriate brand</td>
			<td></td>
			<td>Interface connection</td>
		</tr>
		<tr>
			<td>Octenisept</td>
			<td>SCH&#220;LKE &#38; MAYR GmbH</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Open Broadcaster Software</td>
			<td>Open source</td>
			<td>https://obsproject.com/</td>
			<td>Video recording software</td>
		</tr>
		<tr>
			<td>Spongostan</td>
			<td>&#160;Ethicon</td>
			<td>N/A</td>
			<td>Resorbable sponge</td>
		</tr>
		<tr>
			<td>Ultracain 1%</td>
			<td>&#160;Suprarenin, Sanofi</td>
			<td>N/A</td>
			<td>Local anesthesia</td>
		</tr>
	</tbody>
</table>

performing repeated intraoperative impedance telemetry measurements during cochlear implantation

Impedance measurements are routinely performed during cochlear implantation (CI) after finalized electrode insertion. They may allow conclusions on the electrode's and implant's function. In the postoperative setting, the analysis of impedance changes enables the identification of scarring or inflammation processes around the electrode. Recent studies report associations between impedance telemetry and the site of stimulation. Consequently, repeated impedance measurements during cochlear implant electrode insertion may enable objective feedback on whether the electrode is positioned inside the perilymph or outside the inner ear. With the presented novel method, impedances can be measured in real-time during cochlear implantation. This protocol systematically explains how to perform repeated impedance recordings during CI surgery. These repeated measurements are challenging since they depend on multiple intraoperative methodological factors starting with the draping of the patient. Thus, for successful recordings, a standardized procedure is mandatory. In this article, we comprehensively illustrate the system setup and procedure of performing intraoperative measurements during CI surgery.

Author Spotlight: Advancements in Impedance Monitoring for Cochlear Implant Surgery

Performing Repeated Intraoperative Impedance Telemetry Measurements during Cochlear Implantation

We are working with impedances, since they provide an objective feedback on whether the cochlear implant electrode array is located outside the cochlea or inside the cochlea. High impedances indicate or suggest a poor conductivity, and thus, an electrode contact outside the cochlea. Whereas lower impedances suggest that the conductivity is better, and thus, the electrode contact already inserted.And this information may be used to reduce radiation exposure in the aftercare of cochlear implantation after care. Hearing preservation is an increasing topic of interest in the cochlear implantation field. And with these methods that objectify the position of the electrode array inside the cochlea, and with this, the potentially occurring intracochlear damage are increasingly becoming very important.The current methods for the intraoperative monitoring of the electrode array insertion and the hearing preservation are the electrocochleography and the hear present impedance telemetry. The major tasks to overcome are unexpected high impedances. These high impedances resolve with time and electrical stimulation.Nevertheless, they negatively influence the real-time measurements. We established a method to perform repeated and continuous impedance telemetry measurements, and they open up a whole new perspective on gaining data already during the insertion of a cochlear implant electrode array.

For repeated impedance measurements during cochlear implantation, a standardized procedure is mandatory to achieve the highest possible reproducibility. The major aspects that have been considered to play an important role are the video quality as well as the insertion angle. Both may impede the visualization of the electrode contacts entering the round window and thus, the interpretation of the video for future analyses. Further, the placement of the receiver coil is crucial to prevent interruptions during insertion and...

Watch this Scientific Journal Video about Performing Repeated Intraoperative Impedance Telemetry Measurements during Cochlear Implantation at JoVE.com

Here we present a protocol to conduct repeated impedance telemetry measurements during cochlear implantation (CI). They may allow conclusions on the electrode's and implant's function. Repeated impedance measurements enable objective feedback on whether the electrode is positioned inside the perilymph or outside the inner ear.

Impedance measurements are routinely performed during cochlear implantation (CI) after finalized electrode insertion. They may allow conclusions on the ...

performing-repeated-intraoperative-impedance-telemetry-measurements