Return of Sound Production as a Biomarker of Bottlenose Dolphin Emergence from Anesthesia

SIMPLE SUMMARY: When humans are recovering from an anesthetic procedure, their medical care teams monitor a number of medical and behavioral biomarkers to ensure they are conscious and can safely return home from the hospital. For example, the ability of the patient to open their eyes, track objects, navigate their environment, speak, and respond appropriately to questions, are considered important supplemental behavioral biomarkers. We set out to monitor the return of sound production in bottlenose dolphins as they recovered following anesthesia. Sound production in dolphins is important for both their ability to navigate underwater using echolocation and to communicate with conspecifics using whistles. We found that otherwise healthy dolphins recovering from an anesthetic procedure produced echolocation clicks approximately 92 min following the return of spontaneous breathing. This return was correlated to the return of the righting reflex, or the dolphin’s ability to maintain balance in the water. Whistle production, used for communication, began after the emission of clicks. We suggest that underwater acoustic monitoring of bottlenose dolphins provides useful information to supplement other medical biomarkers of anesthetic recovery. ABSTRACT: (1) Background: When a human or animal is recovering from general anesthesia, their medical team uses several behavioral and physiological parameters to assess their emergence from the unconscious state to complete wakefulness. However, the return of auditory and acoustic behaviors indicative of the complete return of consciousness in humans can be difficult to assess in a completely aquatic non-human mammal. Dolphins produce sound using the nasal system while using both passive auditory and active biological sonar (echolocation) to navigate and interrogate their environment. The sounds generated by dolphins, such as whistles and clicks, however, can be difficult to hear when the animal is submerged. (2) Methods: We implemented a system to audibly and visually (i.e., using spectrograms) monitor the underwater acoustic behavior of dolphins recovering from anesthesia. (3) Results: Eleven of the twelve recorded dolphins began echolocating within 92 min (Mean = 00:43:41 HH:MM:SS) following spontaneous respirations. In all cases, the dolphins echolocated prior to whistling (Mean = 04:57:47). The return of echolocation was significantly correlated to the return of the righting reflex (Mean = 1:13:44), a commonly used behavioral indicator of dolphin emergence. (4) Conclusions: We suggest that acoustic monitoring for the onset of click production may be a useful supplement to the established medical and behavioral biomarkers of restoring consciousness following anesthesia in bottlenose dolphins.