ANESTHESIA WITH FLUNITRAZEPAM TENTANYL AN D ISOFLURANE FENTANYL - UNCONSCIOUS PERCEPTION AND MIDLATENCY AUDITORY-EVOKED POTENTIALS

There is a high incidence of intra-operative awareness during cardiac surgery. Mid-latency auditory evoked potentials (MLAEP) reflect the pr imary cortical processing of auditory stimuli. In the present study, w e investigated MLAEP and explicit and implicit memory for information presented during cardiac anaesthesia. Patients and methods. Institutio nal approval and informed consent was obtained in 30 patients schedule d for elective cardiac surgery. Anaesthesia was induced in group I (n = 10) with flunitrazepam/fentanyl (0.01 mg/kg) and maintained with flu nitrazepam/ fentanyl (1.2 mg/h). The patients in group II (n = 10) rec eived etomidate (0.25 mg/kg) and fentanyl (0.005 mg/kg) for induction and isoflurane (0.6-1.2 vol%)/fentanyl (1.2 mg/h) for maintenance of g eneral anaesthesia. Group III (n = 10) served as a control and patient s were anaesthetized as in I or II. After sternotomy an audiotape that included an implicit memory task was presented to the patients in gro ups I and II. The story of Robinson Crusoe was told, and it was sugges ted to the patients that they remember Robinson Crusoe when asked what they associated with the word Friday 3-5 days postoperatively. Audito ry evoked potentials were recorded awake and during general anaesthesi a before and after the audiotape presentation on vertex (positive) and mastoids on both sides (negative). Auditory clicks were presented bin aurally at 70 dBnHL at a rate of 9.3 Hz. Using the electrodiagnostic s ystem Pathfinder I (Nicolet), 1000 successive stimulus responses were averaged over a 100 ms poststimulus interval and analyzed off-line. La tencies of the peak V, Na, Pa were measured. V belongs to the brain-st em-generated potentials, which demonstrates that auditory stimuli were correctly transduced. Na, Pa are generated in the primary auditory co rtex of the temporal lobe and are the electrophysiological correlate o f the primary cortical processing of the auditory stimuli. Results. No ne of the patients had an explicit memory of intraoperative events. Fi ve patients in group I, one patient in group II, and no patients in gr oup III showed implicit memory of the intraoperative tape message. The y remembered Robinson Crusoe spontaneously when they were asked their associations with Friday. In the awake state AEP peak latencies were i n the normal range. During general anaesthesia in group I, the peaks N a, Pa did not increase in latency or decrease in amplitude before and after the audiotape presentation. The primary cortical complex Na/Pa c ould be identified as in the awake state. In contrast, in group II Na, Pa showed a marked increase in latency and a decrease in amplitude or were completely suppressed. Conclusions. During general anaesthesia a uditory information can be processed and remembered postoperatively by an implicit memory function, when the electrophysiological conditions of primary cortical stimuli processing is preserved. Implicit memory can be observed more often when high-dose opioid analgesia is combined with receptor-binding agents like the benzodiazepines than under non- specific anaesthetics like isoflurane. Non-specific anaesthetics seem to provide a more effective suppression of auditory stimuli processing than receptor-specific agents.