Do anesthetized animals hear, and do the types of auditory stimuli they experience impact their vital signs? Multiple published studies in humans support the concept that individuals under general anesthesia can hear. Music is also known to affect physiologic activity in humans, including those functions controlled by the autonomic nervous system (ANS), such as respiratory and heart rates, body temperature, and pupil constriction and dilation. In children, employment of music in the perioperative period has been shown to reduce perceived pain, anxiety, and stress, as well as decrease anesthetic and analgesic requirements. There have also been a number of studies demonstrating the influence of various types of music on the productivity of food animal species such as dairy cattle and chickens.
General anesthesia also substantially affects the ANS in that it depresses many of its functions in a dose-dependent fashion, so physiologic parameters such as respiratory rate and pupil diameter are useful in evaluating a patient's anesthetic depth. These researchers were interested in determining whether cats under general anesthesia process auditory stimuli, and how various types of music may change an anesthetized patient's physiologic parameters and anesthetic depth.
In this study, the responses of 12 young (6-12 months), healthy female cats undergoing elective ovariohysterectomy surgery to various types of music at critical time points during the surgery when the activity was likely to be painful, were evaluated by monitoring respiratory rate and pupillary diameter. The music was delivered at a volume < 80 decibels to the patients through headphones that completely covered the patient's ears.
Each cat was exposed to a two-minute excerpt of music from 3 different genres: classical, pop, and heavy metal at three different points during the surgery (T1: celiotomy; T2: ligature placement and transection of the ovarian pedicle; T3: ligature placement and transection of the uterine body). Patients were first assessed in silence at each time point as a self-control prior to being evaluated under the influence of music. The selections played were Samuel Barber's "Adagio for Strings (Opus 11)", classical; "Torn" by Natalie Imbruglia, pop; and "Thunderstruck" by AC/DC, heavy metal.
Respiratory rates were evaluated after the patients achieved a stable plane of anesthesia. At all time points, most of the patients had the lowest respiratory rates when exposed to classical music, intermediate respiratory rates when the pop music was played, and the highest respiratory rates during the heavy metal selection. Pupillary dilation measures followed the same pattern at all time points: pupils were least dilated (highest parasympathetic tone) during exposure to classical music and most dilated (highest sympathetic tone) when the heavy metal was played; intermediate sized pupils were noted when the pop music was on.
Use of various musical genres in the surgical setting impacts the physiologic responses of anesthetized patients. Selection of music that may contribute to a decrease in anesthetic dose promotes patient safety, and may, as has been demonstrated in children in the perioperative period, reduce patient pain, anxiety, and stress. In addition, given today's emphasis on "cat friendly" and "fear free" considerations in small animal veterinary practices, conscious attention to music genres played in waiting rooms, boarding and kenneling spaces, and treatment areas may also contribute to the comfort and relaxation of awake patients.
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