THE EFFECT OF GENERAL-ANESTHESIA ON INTRA OPERATIVE ELECTRICALLY-EVOKED STAPEDIUS REFLEX MEASUREMENT

Evaluation of the intraoperative electrically evoked stapedius reflexe s during cochlear implant surgery has two purposes: (1) The functionin g of the device and the peripheral auditory pathways can be proven imm ediately and (2) The data of reflex threshold can be used for the pred iction of later threshold (T)- and maximum comfortable (C) levels. Thi s is especially useful for the later fitting of the speech processor i n very young children. When trying to use the stapedius reflex data fo r the prediction of T- and C-levels it must be considered that during surgery the drugs used for general anaesthesia influence the values of the stapedius reflex. Depending on the drug, the stapedius reflex thr eshold can be increased or the reflex can even be totally blocked. Thi s is not only due to relaxants but also to anaesthetics. To investigat e this influene we first determined the acoustically evoked stapedius reflex threshold in normal hearing adults under general anaesthesia wi th 7 different anaesthetics without additional relaxation. It was foun d that especially with Dormicum(R) and Brevimytala the stapedius thres hold increased only very lightly or did not change at all. In a second investigation the electrically evoked stapedius reflex thresholds wer e obtained in adults who underwent a cochlear implant surgery using th e same anaesthetics for anaesthesia. The intraoperatively evaluated re flex data were compared with postoperatively obtained data. It was fou nd that both reflex thresholds were similar if evaluated in Dormicum(R ) or Brevimytal(R) anaesthesia. This suggests that only with the use o f the right anaesthetics the data of the electrically evoked stapedius reflex obtained intraoperatively can be used for predicting T- and C- levels.