Optimizing Intraoperative Hearing Monitoring in Middle Ear Surgeries: A Preliminary Study of the Modified Auditory Steady-State Responses Measurement Method With Different Electrode Placement and Masking

Objective: To optimize the procedure of auditory steady-state responses (ASSR) for monitoring hearing function during middle ear surgery. Study design: A prospective study. Setting: Tertiary hospital. Patients: A total of 80 patients with conductive hearing loss who underwent middle ear surgeries were included in the study to analyze the effectiveness of the modified ASSR. Another 6 patients with unilateral sudden deafness and contralateral normal hearing were included to evaluate the interaural attenuation value of the sound field speaker. Interventions: Changing the placement of reference electrode to avoid disrupting the surgical process, and applying contralateral masking to improve ASSR threshold accuracy. Main outcome measure(s): Preoperative pure-tone audiometry (PTA) and intraoperative ASSR threshold were collected. The correlation coefficients between ASSR threshold from different electrode placements and between ASSR and PTA from the same patient were analyzed. Results: High correlation coefficients (0.6232 to 0.8766) were observed for mastoid and mandibular electrode placements across all frequencies. Without contralateral masking, ASSR thresholds correlated well with PTA thresholds at 1, 2, and 4 kHz, except for 500 Hz (r = 0.2747). For patients with binaural PTA differences >25 dB, contralateral masking significantly improved the 500 Hz correlation coefficient to 0.5981 and increased the mean correlation index across all frequencies from 0.6111 to 0.7621. Conclusions: Changing the placement of the reference electrode is feasible, and applying contralateral masking is necessary for patients with binaural PTA differences exceeding 25 dB.