Background: Midlatency auditory evoked responses (MLAER) can distinguish different stages of anaesthesia. We studied MLAER during emergence from propofol/sufentanil anaesthesia in relation to recovery of explicit memory.
Methods: MLAER were recorded in 29 healthy patients before and during anaesthesia and during emergence until the patients opened their eyes spontaneously. After a structured interview the next day, patients were classified into those with and without explicit memory of the recovery period. Latencies Na, Pa and Nb and the peak-to-peak amplitudes NaPa and PaNb were compared between the groups by multivariate analysis of variance. Results are mean (SD).
Results: At eye opening (37 (12) min after the end of anaesthesia) the latency Nb (47 (5) compared with 41 (5) ms; P < 0.001) was prolonged and the amplitude PaNb (1.3 (0.8) compared with I (0.5) ms; P = 0.012) was greater than the baseline value, respectively. The Nb latency was significantly shorter in patients with explicit memory (49 (2) ms compared with 45 (I); P = 0.041).
Conclusions: Large intra- and inter-individual variability in the MLAER values limited their ability to predict memory responses in individual patients during emergence from propofol/sufentanil anaesthesia.