CRNA : the clinical forum for nurse anesthetists
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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. ⋯ 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.
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The possibility of awareness during general anesthesia causes apprehension for the patient and the Certified Registered Nurse Anesthetist (CRNA). The goals of general anesthesia are to prevent the sensation of pain and produce a state of sedation, hypnosis, and unconsciousness so the patient will not remember the surgical procedure. An inadequate level of anesthesia can result in patient awareness during surgery. ⋯ The EEG signal is complex, affected by artifact, and it requires a dedicated interpreter. Conventional processed EEG monitoring systems are problematic because of the complexity of the equipment and technical difficulty of reading the EEG recording. The purpose of this article is to describe the history of awareness during anesthesia and introduce a new processed EEG monitor, the Bispectral Index (BIS) (Aspect Medical Systems, Inc., Natick, MA) with implications for future clinical use and research.