Propofol has minimal or no effect on the threshold of the acoustically evoked stapedius reflex

Today cochlear implantation is a widely used therapeutic approach for the treatment of deafness and severe hearing disorders. Postoperative fitting of the externally worn speech processor is very important for successful use of the cochlear implant. Intraoperatively measured stapedius reflex [SR] threshold values are routinely used for programming the speech processor. However, anaesthetic agents can increase the SR threshold up to total blockade. Unlike previous studies, which used various anaesthetic combinations, the aim of the present study was to evaluate substance-specific effects of propofol on the threshold of the acoustically evoked SR in normal hearing. Subjects Twenty patients undergoing elective ENT surgical procedures participated in this study. On the day before surgery, pure tone audiogram and immitance metry were done to help proper selection of patients. None of the patients received any premedication. Anaesthesia was induced with i.v. propofol in a dose of 1.5-2.5mg/kg BW. After induction of anaesthesia and loss of eyelid reflex, tympanometry and ipsilateral and contralateral SR measurement were performed. Statistical analysis included the arithmetic mean, standard deviation, standard error and hypothesis Student's [t] test, p-values <0.05 were considered significant. After i.v. injection of propofol, 17 out of 20 patients showed either no change or a slight, but statistically non-significant elevation of the SR threshold both ipsilaterally and contralaterally at all stimulus frequencies [p>0.05]. Paradoxically, three patients showed variable, yet statistically non-significant reductions in SR threshold at 500, 1000 and 4000 Hz. The results presented in this study show that propofol in a dose of 1.5-2.5mg/kg BW appears to influence the acoustically evoked SR threshold only very slightly, if at all provided it is administered as a sole anaesthetic. Thus. propofol can be especially suitable for anaesthesia in audio-logical diagnostic procedures. We recommed conducting a similar study on a larger group of patients combined with monitoring of the degree of hyponsis

Effect of middle ear effusion on distortion product otoacoustic emissions

Otitis media with effusion is a very common childhood disease which has negative effects on the feasibility of recording of otoacoustic emissions. The aim of the present study was to determine the influence of different types of effusion on distortion product otoacoustic emissions [DPOAE]. Preoperative and first postoperative day DPOAE signal to noise ratio were compared in 50 children [100 ears] undergoing myringotomy and/ or tympanostomy tube insertion for secretary otitis media. The results were analyzed by paired samples test and ANOVA. In the preoperative evaluation, glue effusion caused a significant reduction in DPOAE at 2, 4 and 8 kHz [p<0.05] compared to serous or mucous effusion. Comparison between preoperative and first postoperative day DPOAE signal to noise ratios showed significant differences at 1, 1.5, 2 and 4 kHz [p< 0.05]. On the first postoperative day, the maximum increase in emission was observed at 2 kHz in ears which previously showed glue effusion. Glue effusion causes a reduction in DPOAEs at 2, 4 and 8 kHz more than other types of effusion

Changes in otoacoustic emissions by inducation dose of propofol

The effects of propofol on distortion product otoacoustic emission [DPOAE] recordings were evaluated and compared in the awake and anaesthetized state in a group of twenty ASA I patients undergoing elective surgery of the nose, paranasal sinuses or soft tissue of the neck and throat. We report a statistically non-significant reduction [P> 0.05] in the amplitudes of DPOAEs across all frequency bands following induction doses of propofol. The greatest reduction occurred in the 2 kHz region, where the DPOAE amplitudes were significantly positively correlated with the diastolic blood pressure [r=0.955, P < 0.05]. Our data support the hypothesis that anaesthetic agents produce a frequency-specific attenuation of the DPOAE amplitude and strongly suggest that DPOAE amplitude changes depend not only on the anaesthetic agents pharmacological properties, but on the induced haemodynamic changes as well

Effect of hypotensive anaesthesia on cochlear function

During surgery of the small structures of the middle ear, even minor bleeding can impair the surgeon's ability to operate under an optical microscope. Hypotensive anaesthesia is effective in keeping bleeding to a minimum. However, preliminary results showed that cochlear function was worsened by systemic hypotension which could play a role in the pathogenesis of sudden hearing loss. By recording transient evoked otoacoustic emissions [TEOAEs] in the external auditory canal, the present study was designed to: a- Evaluate the possible auditory functional consequences of cochlear blood flow changes during hypotensive anaesthesia. b- Determine the safe mean arterial blood pressure [MAP] below which cochlear function is deleteriously affected. 20 patients scheduled for middle ear surgery received general anaesthesia with isoflurane. After 15min. of haemodynamic stability, controlled hypotension was induced by an i.v. infusion of glyceryl trinitrate. TEOAEs were recorded in the contralateral ear on the day of surgery prior to admission to the theatre [control value], and then intraoperatively during controlled hypotension at MAP of 65, 60, and 55mmHg, respectively, as well as on the first postoperative day. Statistical analysis included the arithmetic mean, standard deviation, standard error, hypothesis Student's "t", and Pearson's correlation tests. During controlled hypotensive anaesthesia, the intraoperative TEOAE amplitude decreased significantly [p<0.01] and was completely abolished at a MAP