Midlatency somatosensory evoked potentials and explicit memory functions during recovery from propofol/sufentanil anaesthesia

Adequate anaesthesia and avoiding awareness in patients is of major concern for anaesthesiologists during anaesthesia. In a prospective study midlatency somatosensory evoked potentials (SEP) were investigated in relation to explicit memory function during recovery from propofol/sufentanil anaesthesia.

After approval of the local Ethics Committee and written informed consent 20 patients (43 ± 12 years, 71 ± 14 kg, ASA I-II) were included in the study. Anaesthesia was induced with 0.5 μg/kg sufentanil, 2 mg/kg propofol and 0.1 mg/kg vecuronium. After endotracheal intubation and normo-ventilation with FiO₂ 0.3 anaesthesia was maintained with 8 mg/kg/h propofol. SEPs were recorded at Erb, C6 and C4' (N20, P25, N35, P45, N50) following electrical stimulation of the median nerve (3 Hz, intensity of twofold motor threshold, 200/average, bandwidth 0.02–2 kHz). SEP recordings were performed the day before surgery (AWAKE) and during recovery from anaesthesia, until patients were able to identify a shown object (RECOVERY). Monitoring included HR, MAP, P_etCO₂, SaO₂, arm and body temperature. The day after surgery patients were interviewed about their memory of the recovery period and classified into two groups: group 1, no memory; group 2, memory for recovery period. Statistics: Student t-test with P < 0.05 significant.

Patients were able to identify a shown object 26 ± 7 min after the end of anaesthesia (RECOVERY). One day after anaesthesia nine patients did remember events during the recovery period (group 2), while 11 patients did not have any memory (group 1). At RECOVERY latencies P45 (45 ± 6 versus 51 ± 4 ms) and N50 (64 ± 12 versus 78 ± 9 ms) were significantly shorter in the patients of group 2 than in group 1 (P < 0.05). The earlier midlatency SEP components and amplitudes did not differ between the two groups. In conclusion reversal of anaesthesia induced SEP changes of latencies P45 and N50 may indicate recovery of explicit memory functions after anaesthesia.

Figure

Means and SD of SEP latencies 26 ± 6 min after anaesthesia.^*P < 0.05 between patients with (group 2) or without memory (group1) for recovery period after 24 h; n = 20 patients.