Lidocaine in the middle ear.

Anesthesia of the ear canal is produced by injection of lidocaine hydrochloride into the skin of the lateral external ear canal. Ear canal, tympanic membrane, and middle ear surgeries are performed with this injection. The fluid found in the middle ear during tympanotomy was collected and analyzed. The percentage of lidocaine in the fluid was calculated by an enzyme immunoassay technique. Fifteen surgical cases were undertaken in which perilymphatic fluid in the middle ear would not be suspected, such as tympanotomy for otosclerosis. Lidocaine was found in all middle ears in which there was sufficient fluid to collect. The authors question the validity of using the presence of clear fluid in the middle ear, even with reaccumulation, as the sole criterion for identifying perilymph and cerebrospinal fluid.