gms | German Medical Science

Objective: 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 while the patient is under 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.

Methods: ASSR-stimulations were performed in 23 normal hearing patients undergoing craniotomy for different pathologies. ASSR sounds with 1 min. duration, different sound pressures (60, 70, 80 dBSPL), carrier (500, 1000, 2000 Hz) and modulation frequency (40, 90, 110 Hz) were used as stimuli. Stimulation was performed monaurally on the left and on the right without masking of the contralateral ear, as well as binaurally. Evoked responses were recorded using a 2-channel EEG (right/left mastoid vs. vertex) and analyzed using spectral analysis.

Results: Statistically significant responses (p < 0.001) were found in 19 patients with 90 Hz modulation, in 12 patients with 110 Hz and in 8 patients using 40 Hz modulation. Sound pressure levels and carrier frequency significantly correlated with ASSR power.

Conclusions: The presented study demonstrates the usefulness of ASSR during TIVA, with characteristics comparable to those of awake patients. Qualitative ASSR-monitoring employing intraoperative objective audiograms may thus be possible.