The evolution of the auditory midlatency response in evaluating unconscious memory formation during general anesthesia.

The inability to objectively evaluate the amnesic status of an anesthetized patient has been a perplexing problem for the anesthesia provider. One approach thought to be effective in evaluating the amnesic status of the anesthetized patient is the auditory midlatency response (AMLR). The AMLR is an electrophysiological response that is recorded from scalp electrodes 10 to 80 ms after the auditory pathways begin to process acoustic stimuli. The response is thought to reflect the anesthetized patient's ability to consolidate an acoustic stimuli into an explicit or implicit memory. This article defines the amnesic state, describes the various components of AMLR, discusses clinical uses of the AMLR as an indicator of memory formation during the anesthetized state, and explains the clinical implications of using the AMLR in the surgical suite. Recent results have noted that the Pa waveform, the first positive deflection of the AMLR, may be the component that may serve as an intraoperative indicator of the anesthetized patient's ability to potentially consolidate an intraoperative acoustic stimuli into a memory. With the establishment of the Pa waveform of the AMLR as a reliable indicator of intraoperative memory formation, the AMLR can then be used to significantly decrease the occurrences of traumatic neurosis in the surgical patient and subsequent medicolegal consequences for the health care team. Thus, the use of the AMLR strives to promote a safer intraoperative environment for both the patient and the anesthesia provider.