Impedances of Cochlear Implant Electrodes

Objective: The current study investigates

whether, during a Cochlear Implant (CI) surgery, conditioning

(i.e. applying short bursts of electrical stimulation)

within a saline solution can have positive effects on subsequent

intra-operative measurements. We hypothesize that,

based on previous research, the impedance values will be

reduced, and that the reproducibility of Electrically Evoked

Compound Action Potentials (ECAPs) is improved as a

result of conditioning.

Methods: We conditioned half of the electrode contacts,

within a saline solution, before CI insertion, using 23 MEDEL

implants. Impedance was measured for both the conditioned

and non-conditioned groups at five time points.

Repeated ECAP recordings were measured and compared

between the conditioned and non-conditioned groups.

Results: Impedance of the electrode contacts were reduced

by 31% after conditioning in saline solution; however,

there were no clinically relevant differences after

the implantation of the electrode array. The hypothesis

that measurement reproducibility would be increased after

conditioning could not be confirmed with our data.

Within the saline solution, we observed that 44% of the

electrode contacts were covered with air bubbles, which

most disappeared after implantation. However, these air

bubbles limited the effectiveness of the conditioning within

the saline solution. Lastly, the effect of conditioning on the

reference electrode stimulation was approximately 16% of

the total reduction in impedance.

Conclusion: Our data does not suggest that intraoperative

conditioning is clinically required for cochlear implantation

with MED-EL implants. Additionally, an in-vivo ECAP

recording can be considered as a method of conditioning

the electrode contacts.

Significance: We confirm that the common clinical practice

does not need to be changed.