Intraoperative Cochlear Implant Reinsertion Effects Evaluated by Electrode Impedance

Abstract

Objectives: To assess the effect on impedance levels of intraoperative reinsertion of a cochlear implant (CI) array compared with matched controls. Study Design: Retrospective patient review. Setting: Cochlear implant center. Patients: CI recipients in the Sydney Cochlear Implant Centre (SCIC) database who required intraoperative array reinsertion and matched controls. Exclusion criteria; known preceding meningitis or labyrinthitis ossificans; electrode array buckling; incomplete “final” insertion. Intervention: Cochlear implantation. Main Outcome Measures: Impedance values measured intraoperatively, at switch on, 3 months, 6 months, and 12 months postoperatively were analyzed. The Generalized Estimating Equation (GEE) Model was used to compare cases with controls for each device, at each time point, and for each channel. Results: Thirty-one reinsertion cases identified; six CI 422 arrays; 14 CI 24RE (ST) arrays, and 11 CI 512 arrays. No increase in impedance levels was found in the reinsertion cases when compared with their matched controls. The only statistical difference in impedance was seen in the CI 422 cohort at switch on with the reinsertion cases having lower impedances (p = 0.03). Conclusion: This is the first study to examine impedance values in patients who underwent intraoperative CI array reinsertion and to compare them with the impedances of matched controls. No significant increase found in impedances between our reinsertion cases and matched controls, suggesting the reinsertion did not result in any additional trauma or inflammation. This has implications for surgery both in routine cases such as a faulty electrode and also for future design of mechanisms for delivery of intracochlear therapies.

Impedance Change as an Indicator of Cochlear Implant Failure

“…Impedances are measured at each electrode contact along the array, and values may vary from one electrode to another. Factors affecting this variability include the constituent materials, shape, and size of the electrode contacts (9). After the initial activation of the CI, impedance values typically decrease over several weeks before stabilizing (10)(11)(12)(13).…”