Electrode impedance in cochlear implantation: determinants, dynamics, and clinical implications.

PURPOSE: To review the factors influencing electrode impedance, including surgical, biological, and patient-specific factors; to analyze trends in impedance variation and their clinical implications; and to examine the use of impedance as a biomarker in cochlear implantation , along with recent advances aimed at reducing electrode impedance values. METHODS: A narrative review was conducted from 1990 to June 2025, encompassing clinical and experimental studies examining surgical, anatomical, biological, technical, and patient-related factors associated with electrode impedance. First, an automated search was conducted across the main databases to identify all available studies on electrode impedance. A manual search was then conducted to identify additional relevant papers and ensure comprehensive coverage. RESULTS: Screening of approximately 180 publications, followed by review of the relevant ones, revealed that factors such as surgical techniques, correct scala insertion, insertion trauma, patient-specific characteristics, and etiology influence electrode impedance. The observed post-insertion increase in impedance is attributable to tissue reactions, including fibrosis and new bone formation. After CI surgery, impedance typically increases, then declines and stabilizes, generally within 6 months, though this timeline varies with age and other patient-specific factors. Poorer speech outcomes, reduced hearing preservation, and issues such as electrode migration or tip fold-over are associated with abnormal impedance levels. Drug-eluting electrodes, advanced coatings, and early activation are among the new advances that show promise for reducing electrode impedance values. CONCLUSION: Electrode impedance reflects the interactions between the electrode array and the intra-cochlear environment. Understanding the determinants of impedance values and their clinical implications is critical for improving CI users' performance, guiding programming techniques, and reducing complications.