Otolaryngology - Theses
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ItemSystemic steroid protects residual hearing in a guinea pig model of cochlear implantation( 2011)Background: The protection of residual hearing is an important goal of cochlear implant surgery. Local application of steroids to the round window membrane (RWM) of the guinea pig prior to cochleostomy has been shown to protect hearing, but requires a period of pre-treatment for at least one hour. To determine whether this waiting period can be avoided, the efficacy of administering systemic steroids prior to cochlear implantation is investigated. Methods: Seventeen normal hearing guinea pigs were randomly assigned to receive a single preoperative intravenous injection of: 1) normal saline, 2) dexamethasone 0.2 mg/kg or 3) dexamethasone 2 mg/kg, 60 minutes before cochlear implantation. Implantation was completed with a silastic/platinum dummy electrode. Prior to surgery pure tone auditory brainstem response (ABR) thresholds were estimated from both ears separately in response to tone-pips from 2-32 kHz. This was again completed at 1 and 4 weeks postoperatively. The primary outcome measure was threshold shift at 1 and 4 weeks. Histology was examined for evidence of insertion trauma and foreign body reaction. Results: Preoperative injection of 2 mg/kg dexamethasone prevented an elevation in ABR thresholds at all frequencies compared with the control group (8 - 32 kHz) at 1 and 4 weeks post implantation. This protection was not seen with a lower dose (0.2mg/kg) of dexamethasone. There was a foreign body reaction observed in control and low-dose treated animals, however this was suppressed in all but one of the high-dose dexamethasone-treated animals. Conclusions: Intravenous high dose dexamethasone protects hearing during cochlear implantation and prevents the development of an inflammatory histological response. The prolonged intra-operative delay required for local delivery is avoided in this model. Furthermore, it may provide better protection of low frequency hearing than locally administered steroid.