The effect of intravenous injection of lidocaine on the auditory system

Lidocaine hydrochloride was intravenously injected into guinea pigs. Auditory evoked brain stem response (ABR) to clicks, whole nerve action potential (AP) and summating potential (SP) to clicks and 4 kHz tone bursts, and cochlear microphonics (CM) to 4 kHz tone bursts were recorded during a 60 min period following injection. Injection of a small dosage of lidocaine (4 mg/kg body weight) failed to produce any significant change in ABR wave III, AP and CM. However, a large dosage of lidocaine (20 mg/kg) influenced ABR and AP, but had no observable effect on CM. Latency of ABR wave III was prolonged, but its amplitude remained unchanged. Change in the case of 4 kHz tone burst-evoked AP was more pronounced than that in the case of the click-evoked AP. The 4 kHz tone burst-evoked AP showed an initial increase in amplitude, which was followed by a gradual decrease. Latency of both click and 4 kHz tone burst-evoked AP did not show any changes. The amplitude of SP showed more variation during the course of the test period following lidocaine injection than did either ABR or AP, however, SP decreased in its amplitude approximately 60 min after lidocaine injection. Complete disappearance of ABR and AP, followed by recovery of ABR and AP, was observed in animals given a larger dose (30 mg/kg) of lidocaine. CM did not completely die out, and in fact sustained only about a 75% decay in its amplitude. From the above results, it should be concluded that lidocaine, when injected intravenously, affects ABR and AP significantly more than CM.