Factors influencing the efficacy of round window dexamethasone protection of residual hearing post-cochlear implant surgery.
OBJECTIVE
To protect hearing in an experimental model of cochlear implantation by the application of dexamethasone to the round window prior to surgery. The present study examined the dosage and timing relationships required to optimise the hearing protection.


METHODS
Dexamethasone or saline (control) was absorbed into a pledget of the carboxymethylcellulose and hyaluronic acid and applied to the round window of the guinea pig prior to cochlear implantation. The treatment groups were 2% w/v dexamethasone for 30, 60 and 120min; 20% dexamethasone applied for 30min. Auditory sensitivity was determined pre-operatively, and at 1 week after surgery, with pure-tone auditory brainstem response audiometry (2-32kHz). Cochlear implantation was performed via a cochleostomy drilled into the basal turn of the cochlea, into which a miniature cochlear implant dummy electrode was inserted using soft-surgery techniques.


RESULTS
ABR thresholds were elevated after cochlear implantation, maximally at 32kHz and to a lesser extent at lower frequencies. Thresholds were less elevated after dexamethasone treatment, and the hearing protection improved when 2% dexamethasone was applied to the round window for longer periods of time prior to implantation. The time that dexamethasone need be applied to achieve hearing protection could be reduced by increasing the concentration of steroid, with a 20% application for 30min achieving similar levels of protection to a 60min application of 2% dexamethasone.


CONCLUSIONS
Hearing protection is improved by increasing the time that dexamethasone is applied to the round window prior to cochlear implantation, and the waiting time can be reduced by increasing the steroid concentration. These results suggest that the diffusion dexamethasone through the cochlea is the prime determinant of the extent of hearing protection.
Chang
Andrew
A
University of Melbourne, Department of Otolaryngology, Royal Victorian Eye and Ear Hospital, Victoria, Australia.
Eastwood
Hayden
H
Sly
David
D
James
David
D
Richardson
Rachael
R
O'Leary
Stephen
S
D000818:Animals; D019929:Cochlear Implantation / Q000009:adverse effects*; D003054:Cochlear Implants; D003907:Dexamethasone / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D016057:Evoked Potentials, Auditory, Brain Stem; D006168:Guinea Pigs; D034381:Hearing Loss / Q000517:prevention & control* / Q000628:therapy; D012405:Round Window, Ear / Q000187:drug effects* / Q000293:injuries / Q000601:surgery
D003907:Dexamethasone