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This paper is a continuation of studies initiated over two years ago in this laboratory for the purpose of assessing the effects of local anesthetics used topically in otological surgery."! The favorable conditions accompanying the use of topical anesthesia have been discussed there. However, our studies have shown that some of the commonly used anesthetics cause serious disruptions in the action of the cochlea's sensory mechanism when these drugs are applied to middle ear structures. The major effect involves a reduction in the magnitude of the electrical response of the cochlea. These losses have serious implications for hearing. It is clear that the choice of anesthesia for otological surgery is an important matter, and one that demands further systematic study.The purpose of our present research was to determine the effects of lidocaine hydrochloride (Xylocaine® 2, 1, and Y2 per cent solutions with and without 1: 100,000 epinephrine) upon the electrical response of the cochlea of the cat. Also considered was the effect of 1: 100,000 epinephrine alone upon this response. The effects of 10 per cent cocaine hydrochloride and of normal saline are included for comparison. PROCEDURE Twenty-eight cats were used as experimental animals, and each was anesthetized with a solution of diallyl-barbituric acid and ethyl

According to the electrical theory of auditory nerve stimulation the nerve impulses are triggered by the cochlear response, a small potential generated by the hair cells of the cochlea during auditory stimulation. It is apparent, therefore, that any factors which ad versely affect the cochlear response also produce deleterious effects upon hearing, since hearing can be no better than the cochlear poten tial allows.Topical anesthesia is considered by many surgeons to be the method of choice for operations on the ear. If this type of anesthesia is properly employed there will be adequate relaxation, control of bleeding, a margin of safety for the patient, and the co-operation of a conscious patient. 9 However, evidence suggests that certain currently used topical anesthetics produce irreversible losses in the cochlear re sponse when these solutions are employed to anesthetize middle ear structures during surgery. Certain other anesthetics apparently pro duce little or no change in the cochlear response.It is generally known that certain chemical substances depress the actions of living cells. Accordingly, experimental studies of the electrical response of the cochlea have used chemical agents to deter mine whether or not the cochlear response is a physiological potential or nothing more than an artifact.Chemicals were first applied directly to the cochlea by Adrian, Bronk and Phillips. 1 In their inves tigation of the source and nature of the electrical response of the cochlea they injected cocaine solutions through the round window membrane. They observed that the cochlear response diminished rapidly. As a control solution they employed physiological saline,