Effects of round window dexamethasone on residual hearing in a Guinea pig model of cochlear implantation.
To study electric acoustic stimulation, we have developed a model of guinea pig cochlear implantation via a cochleostomy. Thirty minutes prior to implantation, a hyaluronic acid/carboxymethylcellulose bead, loaded with either dexamethasone or normal saline, was placed upon the round window membrane. Animals that did not receive beads acted as controls. Pure-tone auditory brainstem response thresholds were estimated before and after electrode insertion, and 1 and 4 weeks later. Selected cochlear histology was performed.


RESULTS
Dexamethasone could be detected in the cochlea for 24 h after cochlear implantation. Thresholds were elevated across frequencies in all animals immediately after surgery. These thresholds recovered completely at and below 2 kHz, and partially at higher frequencies by 1 week after implantation. At 32 kHz, but not the lower frequencies, the presence of dexamethasone had a significant protective effect upon hearing, which increased in magnitude over time. The protection was greatest in difficult implantations where an intractable resistance to electrode insertion was met. There was a persistent foreign body reaction at the site of implantation of saline-treated implanted ears but not in the dexamethasone-treated implanted ears.


CONCLUSIONS
Short-term preoperative delivery of dexamethasone through the round window can protect residual hearing during cochlear implantation, especially during technically difficult surgery.
Department of Otolaryngology, University of Melbourne, Parkville, Australia. soleary@bionicear.org
David P
DP
James
Hayden
H
Eastwood
Rachael T
RT
Richardson
Stephen J
SJ
O'Leary
D000305:Adrenal Cortex Hormones / Q000494:pharmacology*; D000818:Animals; D001301:Audiometry, Pure-Tone; D019929:Cochlear Implantation; D003907:Dexamethasone / Q000494:pharmacology*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D006168:Guinea Pigs; D006309:Hearing / Q000187:drug effects*; D011183:Postoperative Complications; D012405:Round Window, Ear / Q000187:drug effects*
D000305:Adrenal Cortex Hormones; D003907:Dexamethasone