Effects of cochlear implant surgical technique on post-operative electrode impedance

Intraoperative impedance and ECAP results in cochlear implant recipients with inner ear malformations and normal cochlear anatomy: a retrospective analysis

BACKGROUND

The intraoperative measurements are essential steps in cochlear implant (CI) surgery for confirming correct electrode placement.

OBJECTIVES

To examine the intraoperative impedance and electrically evoked action potential (ECAP) measurement results of cochlear implant (CI) users with normal cochlear anatomy (NCA) and to compare them with CI users with inner ear malformations (IEM).

MATERIAL AND METHODS

This retrospective study included intraoperative data of 300 ears from 258 individuals using Medel® and Cochlear (Nucleus®) CI devices.

RESULTS

Impedance values differed through all regions, and that differences in ECAPs results mainly stemmed from the basal region in Cochlear users, when comparing the impedance values and ECAPs recording prevalence between the NCA and IEM groups, it was observed that there was no significant difference in the impedance values across the intracochlear regions of the groups (apical; p = .26, middle; p = .12, basal; p = .99). However, it was found that the prevalence of measurable ECAPs in all intracochlear regions of the NCA group was higher than the IEM group (p = .000).

CONCLUSION AND SIGNIFICANCE

The robustness of cochlear structures is a crucial factor in the recording of ECAPs. Furthermore, findings in the IEM group demonstrated that proper placement of intracochlear electrodes did not guarantee effective auditory nerve stimulation.

[Neurophysiological parameters for speech recognition in patients with cochlear implants]

OBJECTIVES

 Cochlea Implants (CI) are the preferred treatment for deaf and highly hearing imparied people. While deaf people already profit enormously from any regained hearing perception, it is not as easy to predict a profitable outcome for people with a remaining sense of hearing. To provide patients the best possible outcome in speech understanding, a lot of parameters have to be identified and adjusted. The aim of this study is to show the influence of objective parameters on classified speech understanding using collected data.

MATERIAL AND METHODS

 A total of 52 patients and 65 ears aged between 18 and 80 years were included in this study. ECAP-thresholds from intraoperative measurements and impedance were used as objective parameters. T- and C/M-levels were defined as subjective parameters. To classify the performance the value of speech understanding was used.

RESULTS

 Differences between both groups (age, time after implantation) were not significant. The gained word scores at 500 Hz correlated significantly with the results of the speech perception threshold on two-digit numbers. The electrode impedances correlated on average with speech understanding with constant variability. The distributions of objective and subjective parameters showed partially significant differences. Many distributions showed significant differences to the normal distribution. Accordingly, the overlapping areas of the significance levels are very narrow.

CONCLUSION

 Higher impedances and incorrectly adjusted T-levels resulted in a worse speech understanding. Relation of C/M-levels to ECAP thresholds seem to be crucial for good speech understanding.

Lower initial electrode impedances in minimally invasive cochlear implantation

BACKGROUND

The round window approach and the cochleostomy approach are two widely practiced methods to insert cochlear implant electrode arrays. Yet, there is no consensus on which is more minimally invasive.

OBJECTIVE

To compare the initial electrode impedance (EI) values and the incidence of abnormal electrodes of the round window approach and the cochleostomy approach, and to evaluate the effects of surgical techniques on the intracochlear microenvironment.

MATERIAL AND METHODS

One hundred and seventy-one patients received a unilateral Nucleus cochlear implant. Eighty-two patients were implanted using the round window approach, and 89 patients were implanted using the cochleostomy approach. EI was measured immediately after closure of the incision.

RESULTS

The round window group had lower average initial EI values than the cochleostomy group. For the EI values at each position, statistically significant differences were found in the basal-middle region (Electrode 1-14), but not in the middle-apical region (Electrode 15-22) of the electrode arrays. A lower incidence of high-impedance electrodes was found in the round window group.

CONCLUSIONS

The round window approach leads to lower initial EI and less disturbance to the intracochlear microenvironment.

Electric compound action potentials (ECAPs) and impedances in an open and closed operative site during cochlear implantation

INTRODUCTION

In patients undergoing cochlear implantation, intraoperative measures of impedance and electrically evoked compound action potentials (ECAPs) are used to confirm device integrity and electrode array position. However, these electrophysiological parameters have been shown to decrease over time, with a small decrement observable as early as 24 h post implantation and becoming more apparent after 6 months. Whether the intraoperatively measured impedances and ECAPs recorded immediately after electrode insertion versus later in the operation or in an open versus closed operative site vary has not been documented. Such variation in measurement procedure may affect the ultimate operative outcome.

PATIENTS AND METHODS

Between February and October 2016, 38 patients received a cochlear implant (Cochlear^®), with half receiving a CI 522 device and the other half receiving a CI 512 device. These patients were distributed into three groups. In the first (group A; n = 21), the impedance and threshold neural response telemetry (tNRT) measures were taken before (M1) and after cutaneous suture (M2), whereas in the second group (group B; n = 11) they were taken twice in the open operative site, once at the time of electrode insertion (M1) and then again 10 min later (M2). The last group (group C; n = 6) was measured only once after a 10 min waiting time before closing the operative site.

RESULTS

tNRTs of both group A and B were significantly higher at M1 than measured at M2. The magnitude of change in tNRT did vary significantly by group (P = .027) with group A having a bigger decrease than group B. For impedances there was evidence for a significant difference in M2 between the three groups (P = .012), with group C having significantly higher values compared to group A and B.

CONCLUSION

Intraoperative tNRT measures change significantly over time, including within the first 10 min of implantation. One underlying etiology of this phenomenon for tNRTs seems to be the condition of the surgical site whereas changes of impedances can be best explained by the 'electrochemical cleaning' theory associated with the first stimulation of the electrode. However, for both impedances and tNRTs there also is an important impact of time as well as of acute perioperative changes in electrical conductivity.

Comparable Electrode Impedance and Speech Perception at 12 Months after Cochlear Implantation Using Round Window versus Cochleostomy: An Analysis of 40 Patients

OBJECTIVE

The objective of this study was to examine whether cochlear implantation using the round window (RW) route versus cochleostomy achieves comparable electrode impedance and hearing results.

METHODS

This retrospective analysis included 40 patients receiving a cochlear implant (REZ-1): 20 using the RW approach and the remaining 20 using cochleostomy. Electrode impedance and tone, vowel, consonant, disyllable and sentence perception were measured during and after the implantation.

RESULTS

Electrode impedance did not differ significantly between the 2 groups at any time points [F(1, 38) = 1.84; p = 0.184]: 1.87, 5.16, 6.47 and 6.70 kΩ in the RW group versus 2.86, 5.33, 6.92 and 8.16 kΩ in the cochleostomy group at 0, 1, 3 and 12 months, respectively. There was no significant difference between the RW and cochleostomy groups for tone (77.50 vs. 80.50%; p = 0.472), vowel (77.70 vs. 78.65%; p = 0.760), consonant (75.50 vs. 78.25%; p = 0.443), disyllable (78.60 vs. 81.50%; p = 0.317) and sentence (50.90 vs. 52.50%; p = 0.684) perception at 12 months.

CONCLUSION

The RW approach is comparable to cochleostomy in electrode placement as reflected by impedance and function as reflected by tone, vowel, consonant, disyllable and sentence perception.