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.