Mild Hypothermia Protects Auditory Function During Cochlear Implant Surgery

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Abstract
Objective/Hypothesis: Loss of auditory function after cochlear implant (CI) electrode insertion occurs in two stages in the laboratory rat. An immediate loss is followed by a progressive loss over 7 days. Similar stages of acute and progressive neuronal loss occur after trauma in the central nervous system where hypothermia has been shown to have a protective effect. We hypothesize that hypothermia has a similar protective effect against loss of auditory function caused by CI electrode insertion trauma. Methods: Thirty rats underwent surgery in one cochlea; the contralateral ear was an unoperated control. In the normothermia group, CI electrode insertion trauma was generated with rectal temperature maintained at 37°C throughout the experiment. In the mild hypothermia group, electrode trauma was generated with rectal temperature lowered to 34°C. In the surgical control group, mock surgery was performed at 37°C. Multiple frequency auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) testing of all ears was performed before surgery, immediately afterward, and on postoperative days 3, 5, and 7. Results: Both ABR and DPOAE testing demonstrated partial loss of auditory function after electrode insertion trauma. However, the hypothermia group had significantly less functional loss in the immediate stage and no significant loss in the progressive stage. Conclusion: Mild hypothermia protects auditory function during CI electrode insertion.