Change in endocochlear potential during experimental insertion of a simulated cochlear implant electrode in the guinea pig.
OBJECTIVE
Preservation of residual hearing during cochlear implantation is important. This study investigated changes in endocochlear potential (EP) during simulated cochlear implant (CI) electrode insertion.


METHODS
Laboratory animal study.


METHODS
Academic hospital laboratory.


METHODS
Guinea pigs were divided into 4 groups: cochleostomy only (4 animals), suction after cochleostomy (5 animals), simulated CI electrode insertion parallel to the longitudinal axis of the scala tympani without suctioning (7 animals), and simulated CI electrode insertion toward the modiolus without suctioning (7 animals). The EP was measured from the second turn of the cochlea, and the values after 20 minutes were compared.


RESULTS
The EP showed little change at 20 minutes after cochleostomy with a nearly normal value of 84.83 ± 2.12 mV. Suctioning of the perilymph from the cochleostomy site caused a slight acute reduction in EP by about 6 mV, and the value at 20 minutes after cochleostomy was 78.64 ± 4.42 mV. Insertion of the simulated CI electrode parallel to the longitudinal axis of the scala tympani caused a slight decrease in EP to 78.91 ± 5.06 mV. Insertion toward the modiolus caused a marked decrease in EP to 54.13 ± 4.42 mV at 20 minutes after the treatment, significantly lower compared with the other 3 groups.


CONCLUSIONS
EP was well preserved during carefully performed surgical procedures of simulated CI electrode insertion, but it decreased significantly if the simulated CI electrode was inserted toward the modiolus. Careful attention is necessary to ensure the correct direction of CI electrode insertion to preserve residual hearing. Use of suction should be minimized if possible.
*Department of Otolaryngology-Head and Neck Surgery, Tohoku University School of Medicine; and †Division of Otorhinolaryngology, Sendai Municipal Hospital, Sendai, Japan.
Hidetoshi
H
Oshima
Ryoukichi
R
Ikeda
Kazuhiro
K
Nomura
Muneharu
M
Yamazaki
Hiroshi
H
Hidaka
Yukio
Y
Katori
Takeshi
T
Oshima
Tetsuaki
T
Kawase
Toshimitsu
T
Kobayashi
D000818:Animals; D003051:Cochlea / Q000502:physiology* / Q000601:surgery; D019929:Cochlear Implantation; D003054:Cochlear Implants; D006168:Guinea Pigs; D008297:Male; D008564:Membrane Potentials / Q000502:physiology*; D010498:Perilymph; D012533:Scala Tympani / Q000502:physiology* / Q000601:surgery