Subconscious Auditory Processing in Anesthesia: The Common Theme Between Dreams, Implicit Memory and Anesthesia Awareness

Abstract

The fact that auditory evoked potentials (AEPs) have been used widely as a measure of the depth of anesthesia highlights the importance of auditory modality in consciousness-related neural processing during anesthesia, a phenomena more specifically known as Intra-operative awareness (IOA). The phenomena of IOA has seldom been observed from the perspective of consciousness itself. This perspective is especially important because the dimensions of IOA exist in the subconscious domain of mind as much as they exist in the conscious domain of explicit recall. Two important aspects of these subconscious manifestations of IOA are the implicit recall phenomena and post-operative dreams related to anesthesia experiences. Here we present an integrated auditory-consciousness based model of IOA. We start with a brief description of auditory awareness and the factors affecting it. Further, we proceed to the evaluation of conscious and sub-conscious information processing by auditory modality and their interactions during and after intraoperative period. Further, we show that both conscious and subconscious auditory processing affect the IOA experience and both have serious psychological implications on the patient subsequently. These effects could be prevented by using auditory evoked potential during monitoring of anesthesia, especially the Mid-latency Auditory Evoked Potentials (MLAERs). To conclude, we propose that the use of Auditory evoked potential should be universal with general anesthesia use in order to prevent the occurrences of distressing outcomes resulting from both conscious and subconscious auditory processing during anesthesia.