Dexamethasone abolishes intra-day fluctuations of electrode impedance in cochlear implant users

Dexamethasone-eluting cochlear implant (CI) electrode arrays aim to reduce mean electrode impedance and enhance stability. However, longitudinal data on intra-day impedance dynamics are lacking. This study compared postoperative impedance profiles between users of dexamethasone-eluting FLEX28 (DEX) and conventional FLEX28 (NoDEX) electrodes, focusing on mean impedance levels and intra-day fluctuations.

Participants were assigned to DEX or NoDEX groups based on electrode type. Both groups measured impedance twice daily (morning and evening) for four months postoperatively via an app. Primary outcomes were mean impedance levels and intra-day fluctuations, represented by the morning-to-evening difference (MED). Analyses were conducted descriptively and by group comparisons using the start of electrical stimulation (t₀) as reference. Four postoperative phases were examined: early postoperative (days 1-10), late postoperative (day 11-t₀), intensive fitting (t₀-day 21), and regular hearing phase (day 22-4 months).

The DEX group exhibited consistently low and stable impedance values throughout, with no detectable effect of the start of electrical stimulation (t₀). Daily impedance was consistently lower in DEX than in NoDEX, but the differences reached high statistical significance from the late postoperative phase onward (p < 0.0001). Intra-day fluctuations were abolished in DEX (MED ≈ 0), whereas NoDEX showed measurable fluctuations during intensive fitting (DEX: 0.0 kΩ, n = 7 vs. NoDEX: 0.75 kΩ, n = 11; p < 0.001) and regular hearing phase (DEX: 0.0 kΩ, n = 8 vs. NoDEX: 0.56 kΩ, n = 11; p = 0.02).

Dexamethasone-eluting FLEX28 electrodes not only reduce mean impedance but also maintain stable values over time and effectively abolish intra-day fluctuations.