Implicit memory varies as a function of hypnotic electroencephalogram stage in surgical patients.

UNLABELLED: Previous studies have observed a correlation of implicit memory with certain electroencephalogram (EEG) measures during anesthesia. Here, we tested the relationship between hypnotic depth determined by computer system (Narcotrend(TM)) and implicit memory in anesthetized patients, assessed by a postoperative reading speed test. Thirty-two patients undergoing laparoscopic herniotomy and 30 age-matched volunteer controls were included the study. All patients received IV midazolam 2-3 mg followed by an induction dose of propofol and remifentanil. The anesthesia was maintained with propofol and remifentanil infusions and cisatracurium. Each patient was exposed to 2 of 4 stories, repeated 6 times. The first story was presented during light to moderate hypnotic EEG stages, and the second story was presented during deep hypnosis. Presentation of stories was balanced between patients and hypnotic stages. The controls listened to the two stories without receiving anesthesia. The reading speed for the previously presented stories and two new stories was measured approximately 7 h later with a computer program. No signs of inadequate anesthesia were observed, and no explicit memories of intraoperative events were revealed by a structured interview. No change of reading speed was observed for words presented during deep hypnotic stages. In contrast, an increased reading speed of 20 ms per word was found for content words (i.e., nouns, verbs, and adjectives), but not for function words (conjunctions, prepositions, and so on), presented during light to moderate hypnotic stages. Increased reading speed for semantically rich content words indicates that anesthetized patients are able to process acoustic information during light and moderate, but not deep, hypnosis. IMPLICATIONS: In this study, implicit memory was observed during general anesthesia at light to moderate, but not deep, hypnotic stages. Hypnotic stages were determined by a commercial electroencephalogram device, and implicit memory was measured by using a postoperative reading speed task. During lighter phases of anesthesia, patients should be protected against acoustic information that could negatively influence their postoperative outcome.

Electroencephalogram monitoring facilitates sedation with propofol for routine ERCP: a randomized, controlled trial.

BACKGROUND: Endoscopy with the patient under sedation with propofol requires careful monitoring of patient consciousness and vital signs to achieve the desired hypnotic effect without overdosage. Because level of consciousness is difficult to judge by clinical observation alone, electroencephalogram monitoring has been used to guide general anesthesia. METHODS: Eighty consecutive patients (mean [SD] age 62 [14] years) undergoing ERCP for various indications were randomly allocated to 2 groups. In group A (n = 40), propofol sedation was guided by conventional monitoring (heart rate, blood pressure, oxygen saturation, electrocardiogram), whereas electroencephalogram monitoring was performed but not displayed to the physician who administered the drug. In group B (n = 40), electroencephalogram monitoring was displayed online and used to guide propofol administration to maintain a preselected sedation level. Procedure-related parameters, recovery time, and quality (postanesthesia recovery score), as well as patient cooperation and tolerance for the procedure (visual analog scale) were prospectively assessed. RESULTS: The groups were comparable with regard to demographic, clinical, and procedure-related parameters. Mean propofol dose was significantly lower in group B than in group A (respectively, 290 [158] mg vs. 374 [166] mg; p = 0.02). The mean decrease in arterial blood pressure was significantly lower in group B than in group A (respectively, 11 [6] mm Hg vs. 14 [7] mm Hg; p < 0.05). Clinically relevant changes in vital signs to below critical values were observed in both groups, albeit infrequently. Efficacy of sedation was also rated similar in both groups, whereas mean recovery time was significantly faster in group B than in group A (respectively, 16 [7] minutes vs. 20 [8] minutes; p = 0.02). Accordingly, the recovery score tended to be better in group B compared with group A (respectively, 8.4 [1.0] points vs. 8.0 [0.9] points; p = 0.06). The predefined target level of sedation was maintained during 75% of the procedure time in group B but in only 58% of the time in group A (p < 0.05), and deeper sedation levels were achieved significantly more often in group B patients compared with group A patients (p < 0.05). CONCLUSION: Electroencephalogram monitoring enables more effective titration of propofol dosage for sedation during endoscopy and is, therefore, associated with faster patient recovery.