Effects of ropivacaine on transient-evoked otoacoustic emissions: a rabbit model

The aim of this study was to investigate the effect of ropivacaine, a newer amide local anesthetic, on the ears of rabbits by using transient-evoked otoacoustic emissions (TEOAEs). Thirty rabbits were studied in a random block design of six groups of five animals each. There received intra-tympanically instilled single doses of 0.5 mg/kg, 1.0 mg/kg of ropivacaine, 0.5 ml of isotonic saline (control for intratympanic application), or intravenously administered single doses of 1.0 mg/kg, 2.0 mg/kg of ropivacaine and 1.0 ml of isotonic saline (control for intravenous application). Cochlear function was serially monitored using TEOAEs before administration and on the 1st and 15th days after administrations of ropivacaine or isotonic saline. The responses of TEOAEs were analyzed in terms of mean stimulus, stability, wave reproducibility and emission amplitudes at 1.0-4.0 kHz. We found no significant changes in the TEOAE responses of the baseline measurements in each group before administration and the responses at each interval in the same group after administration throughout the experiment (P > 0.05). Also, no significant difference was found between the group receiving ropivacaine administered intravenously or intratympanicly and the control group at each interval (P > 0.05). The data from the present study showed that ropivacaine, whether administered intravenously or intratympanically and even at a low or high dose, has no effects on the responses of TEOAEs in the early period. These findings encourage the use of ropivacaine as a safe agent without ototoxic effects in peripheral nerve blocks, epidural and intravenous regional anesthesia or even tinnitus therapy in the future.