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

ABSTRACT

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