Long-term impedance dynamics of cochlear implant electrodes in children

Background. Nowadays in Ukraine, there are about 3 thousand cochlear implant users, and their number is constantly increasing. The internal part of the implant remains in the cochlea throughout the patient’s life, but current data on the state of the electrodes in the long-term period are contradictory. The purpose was to study the impedance dynamics of cochlear implant electrodes during 5 years after surgery in children. Materials and methods. A retrospective study of 58 children with deafness after cochlear implantation was conducted. The changes in the interelectrode impedance and the relationship between them in the different parts of the electrode were evaluated and analyzed 1, 2, 3, and 5 years after the start of electrical stimulation. Results. At 1 year after the connection of the speech processor, an increase in the impedance was recorded in the basal part of the electrode (9–12 channels) relative to the medial and apical part of the cochlea. Over the next year, according to the electric field telemetry data, a significant (p < 0.05) downward trend was noted in the resistance in the basal part of the implant (9–12 electrodes). Within 2–5 years, a gradual decrease in the impedance in the medial and apical parts of the electrode occurred without statistically significant differences. In 29.3 % of cases, there was a tendency to a gradual increase in the impedance on 11–12 electrodes within 3–5 years after surgery. In another 8 patients (13.8 %), a critical increase in the impedance (> 15 kilohm) was detected on one of the contacts in the basal part of the electrode, which required their disconnection or correcting the settings of the speech processor. Conclusions. Regular monitoring of electrode impedance and electrical stimulation levels is recommended, especially during the first 2 years of implant use. This is necessary to improve the performance of the implant, to determine the most comfortable levels and thresholds of volume more accurately, which will improve the sound perception in children after cochlear implantation.