Ambient Music Decreases EEG Burst-Suppression Ratio During General Anesthesia in Rats

During deep anesthesia, the EEG becomes discontinuous. Burst-suppression is often an intended target during deep sedation or medically induced coma. Within this state, anesthetic depth is commonly monitored by the suppression ratio (SR), which expresses the fraction of time spent in suppression. However, accumulating evidence suggests that SR remains reactive to external stimulation. We tested whether ambient music commonly played in operating theaters alters the SR in male Wistar rats under sevoflurane, chloral hydrate, or isoflurane anesthesia. To this end, the first 60 s of the Stayin' Alive audio track by the Bee Gees were played to examine auditory-induced burst-suppression reactivity in an experimental model previously established for intermittent photic stimulation. SR and the burst-suppression reactivity index (BSRi, derived as the decrease in SR during stimulation normalized to pre-stimulation SR) were measured in repeated trials. Auditory stimulation transiently decreased SR under all three anesthetics. This was associated with an increase in the rate of burst occurrence without increased burst duration. The BSRi changes depended on the anesthetic type, comparable to photic stimulation. Our experimental data suggest that the suppression ratio used to monitor targeted burst-suppression reflects both anesthetic depth and the level of ambient stimulation. Ambient sound in the operating theater or intensive care settings could influence EEG-based measures used for anesthesia monitoring.