Changes in Intraoperative and Postoperative Neural Response Telemetry in Cochlear Implant Users

Introduction: The cochlear implant directly stimulates the auditory nerve in deaf patients. Neural Response Telemetry (NRT) is used to record the response of the auditory nerve through thefeedback of the electrical signal. NRT does not need behavioral responses from very young
children for thresholds and comfort levels. The status of the cochlear nerve activation with
NRT was reviewed through intraoperative and postoperative neural responses.
Aim of the work: To detect any changes in intraoperative and postoperative neural response telemetry in cochlear implant users.
Patients and Methods:Thirty patients were implanted with a MED-EL device, Sonata II (Med-El, Innsbruck, Austria) at Sohag University hospital. Electrodes 2, 4, 6, 8, 9, 10, 11 and 12 were monitored intraoperatively. One month after surgery, the neural responses were investigated using the same electrodes as during the intraoperative procedures. The corresponding electrodes werethen checked again after another 3 months.Phase duration 30µs, begin by amplitude 200cu increasing in steps each 100cu till get response or reaching maximum level 1200cu (intraoperative) or reached the uncomfortable level of the child (postoperative). Threshold of the neuronal response is calculated using linear equation function.
Results:There is significant improvement in thresholdsof NRTresponse postoperatively which was high intraoperatively. NRT threshold increase in postoperative follow up in comparison with first postoperative measurement but this increase is not statistically significant.
Conclusion: Absence of NRT response in some electrodes intraoperative does not mean that electrode must be out of function or outside the cochlea.