Differences in the impedance of cochlear implant devices within 24 hours of their implantation

Abstract

Cochlear implantation is a surgical procedure, which is performed on severely hearing-impaired patients. Impedance field telemetry is commonly used to determine the integrity of the cochlear implant device during and after surgery. At the Department of Otolaryngology, Cheng Hsin General Hospital (Taipei, Taiwan), the cochlear implant devices are switched on within 24 hours of their implantation. In the present study, the impedance changes of Advanced Bionics™ cochlear implant devices were compared with previous studies and other devices. The aim was to confirm previous hypotheses and to explore other potential associated factors that could influence impedance following cochlear implantation. The current study included 12 patients who underwent cochlear implantation at Cheng Hsin General Hospital with Advanced Bionics cochlear implant devices. The cochlear devices were all switched on within 24 hours of their implantation. The impedance was measured and compared across all contact channels of the electrode, both intra-operatively and post-operatively. The intra-operative impedance was compared with the switch-on impedance (within 24 hours of the cochlear implantation); the impedance was notably increased for all contact channels at switch-on. Of the 16 channels examined, 4 channels had a significant increase in impedance between the intra-operative measurement and the switch-on measurement. To the best of our knowledge, the impedance of a cochlear implant device can be affected by the diameter of the electrode, the position of the electrode arrays in the scala tympani, sheath formation and fibrosis surrounding the electrode after implantation and electrical stimulation during or after surgery. When the results of the current study were compared with previous studies, it was found that the impedance changes were opposite to that of Cochlear™ implant devices. This may be explained by the position of the electrode arrays, sheath formation, the blow-out effect and differences in electrical stimulation.

Evolution of impedance values in cochlear implant patients after early switch-on

“…The difference is not significant between the impedance measured within 24 hours after the implantation and that measured intra-operatively in the present study (Tables 1 and 2 ). This was different to one study of the same system by the authors [ 10 ]. Our previous study was focused on patients who received HiFocus TM 1-J electrode array implantations and the patients in the present study received HiFocus TM Mid-Scala implants.…”

“…The above two reasons could explain the stable impedance on day one. One might wonder that a 1-J array will have more space to develop fibrosis and sheath formation [ 11 , 12 ], which in turn could lead to the sheath formation effect [ 6 , 13 ] and thus a significant increase in impedance as observed in our previous study [ 10 ]. However, a complete sheath can’t be expected to form at day one despite cell cover begins within hours of implantation [ 5 , 7 ].…”

“…However, the impedance in every segment began to be relatively stable 4 weeks after surgery [ 9 ]. On the contrary, we found that the impedance of another manufacture’s device (Advanced Bionics TM , Westinghouse, Pl, USA) increased significantly within 24 hours after the surgery [ 10 ]. However, the long-term variation of impedance for the device remained unknown.…”

Intraoperative Impedance-Based Estimation of Cochlear Implant Electrode Array Insertion Depth

“…For such applications, it should be considered that cochlear implantation causes foreign body reaction, with increased number of macrophages and fibrous tissue build-up surrounding the electrode [42]. This affects the temporal progression of electrode impedances [43]. High impedance values can also be caused by air bubbles on the electrode contact, which generally dissipate within hours to days after the surgery [8], [10].…”

Effect of Initial Switch-On Within 24 Hours of Cochlear Implantation Using Slim Modiolar Electrodes: Potential Clinical Implications

“…Since the e cacy and safety of early switch-on within 24 h of surgery has previously been con rmed 17 , many CI centers, including ours, have changed the switch-on protocol over the past few years from the initial tting at 3-6 weeks post-surgery to the day after surgery. Previous studies investigating the evolution of electrode impedance after early switch-on have shown inconsistent results according to the type of electrode array [18][19][20] . To the best of our knowledge, this is the rst study to describe changes in the impedance of slim modiolar electrodes over time in CI recipients who were rehabilitated with the conventional and early switch-on protocols.…”