Surgical approach to the dolphin's ear

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Abstract
A surgical approach to the cetacean (Tursiops truncatus and Lagenorhynchus obliquidens) ear represented a unique problem. The first obstacle was the development of a safe and humane anesthesia procedure and techniques of long‐term physiological maintenance of the animal during surgery. The surgical anatomy was a challenge especially because of the extensive venous plexuses that invest the entire ear and adnexa. The corpus cavernosum carotidis and other small arterial networks course through this venous mass.Sodium pentothal‐halothane anesthesia and careful physiological monitoring were determined to be adequate for long‐term maintenance during surgery and cochlear recording experiments. A specially designed surgical tank held the animal during the procedure. Immersion in water relieved the lungs of external pressure that ordinarily occurs, when the animal is out of the water, due to the flexible thorax. Thermoregulation was provided for by regulating the water temperature in response to the dolphin's core temperature. This arrangement also provided for underwater auditory stimulation and easy manipulation of the animal since dolphins with their lungs inflated are close to neutral buoyancy.It was necessary to ligate the external and internal carotid arteries, neither of which supplies blood to the ear or brain. Hemostasis in the massive venous plexus could be achieved only by partial removal and subsquent application of oxycel and surgical cement to effectively dam off the area of the round window and other ear structures for electrical potential recording and experimental manipulations.With this technique the round window of the cochlea was exposed. Fully anesthetized animals were maintained for periods up to 24 hours while electrophysiological measurements were being made. Some of the auditory measurements required further surgical manipulation of the auditory meatus, bulla, ossicular chain and other middle‐ear structures.