Application of Intra-operative Neural Response Telemetry in Cochlear Implant

Oh, Soo Hee; Shin, Jung Eun; Lee, Kwang Sun

Abstract

BACKGROUND AND OBJECTIVES
Neural response telemetry (NRT) has been used as one of the most useful tools to measure neural responses ranging from spiral ganglion cells to electrical stimulation via the Nucleus 24 cochlear implant. The purpose of this study was to assess and analyze the result of NRT measured intraopertively and apply the result in postoperative mapping.
SUBJECTS AND METHOD
The NRT test was administered to 72 patients (49 children and 23 adults) with the Nucleus 24 cochlear implant. After inserting of the electrode array into the scala tympani, an impedance test was administered to check the integrity of each inserted electrode. In cases of partial insertion, the electrodes outside the cochlear were excluded along with those proven to be short circuited. The electrically evoked action potential (EAP) was recorded using version 3.0 of NRT software. One intra-cochlear electrode (electrode 2, 4, 6, 8, 10, 12, 14, 16) with MP1 as reference was chosen for the stimulating pair. The recording electrode was located 3 electrodes away apically from the stimulating intracochlear electrode and referenced to MP2. The amplifier gain and sampling delay were optimized for each subject using electrode 4 and these same parameters were used throughout the test.
RESULTS
Out of 72 implantees, 56 patients (78%) were observed to produce reliable responses: 16 (70%) of 23 adults and 40 (82%) of 49 children responded. The patients who failed to produce NRT response had higher T levels than patients who had NRT response.
CONCLUSION
Eighty percent of the implantees without any inner ear anomaly showed reliable response to intraopertive NRT measurement. The intra-operarative NRT data may be used to predict electrical stimulation levels in programming.