Relationship of auditory middle latency response and stem-word completion test as indicators of implicit memory formation during general anesthesia

Abstract

Anesthesia providers are unable to objectively evaluate the amnesic status of an anesthetized patient. One purpose of the study was to evaluate the anesthetized patient's ability to process auditory information while receiving an inhalational or intravenous anesthetic regimen. The other purpose was to examine the relationship of the Pa latency of the auditory middle latency response (AMLR) with the stem-word completion test as an intraoperative indicator of implicit memory formation during general anesthesia. One hundred one adults were randomly assigned in a single-blinded design to either a midazolam or sevoflurane anesthetic regimen. Midazolam was administered at 0.540 microgram/kg per minute with fentanyl and 50% nitrous oxide. The other anesthetic regimen was 1.4% end-tidal concentration of sevoflurane with fentanyl and 50% nitrous oxide. A list of 10 words was repeated 16 times. AMLRs were recorded intraoperatively. The difference between the midazolam groups borderlined statistical significance (P = .07) in illustrating that one may potentially process auditory information while anesthetized. Dissimilar findings were found between the sevoflurane groups (P = .77). An inverse correlation was demonstrated between the midazolam group and Pa latency of the AMLR (r = -0.40, P = .047). Multiple regression of the midazolam group demonstrated that the employment status (r2 = .297, P = .005) and the Pa latency (r2 = .238, P = .003) were the best predictors of the postoperative stem-word completion test (F = 12.61, P = .001). In contrast, no correlation was noted in the sevoflurane group (r = 0.43, P = .07). Thus, the continued evaluation of the AMLR as an intraoperative indicator of implicit memory formation is warranted. With the establishment of the AMLR as an indicator of implicit memory formation during general anesthesia, anesthesia providers could then address the occurrences of traumatic neurosis in the postoperative surgical patient and strive to avoid the medicolegal concerns that may face the healthcare team.