Effect of anesthesia on acoustically evoked middle latency response in guinea pigs

Increased recent interest in the middle latency response (MLR) has necessitated a clarification of the possible effects of anesthesia on the response. Our study was designed to examine the changes, in the guinea pig MLR, which occurred during anesthesia with ketamine, xylazine or both ketamine and xylazine. Under anesthesia the response remained present and the threshold remained stable. After anesthesia, significant changes in amplitude, latency, and general morphology of the waveform took place, however these were consistent and predictable. For studies requiring the MLR, it is best to avoid anesthetic agents. However, with care the MLR can be used as a reliable measure of auditory system sensitivity under anesthesia.