18. Frequency-specific ASSR for intraoperative auditory nerve monitoring

Abstract

Frequency-specific ASSR for intraoperative auditory nerve monitoring S. Rampp, L. Rensch, C. Strauss, J. Prell Klinik und Poliklinik fur Neurochirurgie, Universitatsklinikum Halle (Saale). Introduction For intraoperative monitoring of the cochlear nerve, auditory evoked brainstem potentials (BAEP) have been used for many years. However, BAEP provide only limited information about the expected postoperative hearing quality, e.g. regarding language understanding. In contrast, the ’auditory steady state response’ (ASSR) may enable objective audiograms under general anaesthesia, which could be used to evaluate detailed hearing quality for intraoperative decision making. Clinical studies investigating ASSR in total intravenous anaesthesia (TIVA) have not yet been conducted. The presented study thus aims to evaluate viability of intraoperative ASSR during TIVA. Material and Methods ASSR-stimulation was performed in 9 patients undergoing surgery for vestibular schwannoma or meningioma in the cerebello-pontine angle (CPA). ASSR sounds with 5 min duration, 80 dB nHL, 90 Hz modulation and different carrier frequencies (500, 1000, 2000 Hz) were used as stimuli. Stimulation was performed monaurally on the side of surgery. Evoked responses were recorded intraoperatively using a −2 channel EEG (right/left mastoid vs. vertex) at the beginning and the end of the surgical procedure. ASSR detections were compared to pre- and postoperative hearing class. Results Sensitivity for hearing class A was 96%, specificity was 83% with a positive/negative predictive value (PPV, NPV) of 82%/96%. Sensitivity for serviceable hearing (classes A/B) was 77%, specificity 79%, PPV was 82% and NPV 73%. Conclusion ASSR during CPA surgery are viable and show a strong association with hearing quality. ASSR may thus represent a valuable alternative or complementary method to BAEP for auditory nerve monitoring.