How reliable is visual assessment of the electrically elicited stapedius reflex threshold during cochlear implant surgery, compared with tympanometry?

Objectives: To assess the reliability of visually assessed thresholds of the electrically elicited stapedius reflex, recorded during cochlear implant surgery, compared with intra-operative tympanometric threshold assessment. Intra-operatively recorded electrically elicited stapedius reflex thresholds vary considerably, and differ from those measured post-operatively by means of impedance changes (i.e. using tympanometry). Thus, any confounding effect of different intra-operative techniques and visual assessment inaccuracies should be excluded. Methods: Both techniques (i.e. visual observation and tympanometry) were performed intra-operatively in six patients, and threshold values were compared. Results: Recorded electrically elicited stapedius reflex thresholds were very similar for both techniques. Visually assessed thresholds were slightly higher in some cases and lower in others, compared with tympanometric thresholds. Discussion: There was almost no difference between reflex thresholds measured with the two different techniques under the same intra-operative conditions. Therefore, we conclude that differences between intra- and post-operative thresholds are not due to the use of different measuring techniques. The main reason for such differences is probably the influence of intra-operative narcotics on reflex thresholds.