Assessment of explicit and implicit memories during remimazolam anaesthesia using the process dissociation procedure

BACKGROUND Memory formation during remimazolam anaesthesia, where a bispectral index (BIS) is sometimes not maintained at less than 60 despite the maximal dose, is worthy of evaluation. OBJECTIVE Investigate the formation of explicit and implicit memories using the process dissociation procedure during remimazolam anaesthesia at a BIS of 60 to 80. DESIGN A prospective cohort study. SETTING A tertiary medical centre in Seoul, South Korea, between March 2022 and July 2022. PATIENTS One hundred patients undergoing general anaesthesia using remimazolam. INTERVENTIONS The BIS was maintained at 60 to 80 during anaesthesia induction with remimazolam. Words were spoken to patients via headphones for 15 min. MAIN OUTCOME MEASURE The primary outcome was the probability of explicit or implicit memory formation as calculated using the original and extended models, within 24 h after word presentation. Conscious recall memory was assessed using a short-structured interview within 1 and 24 h after surgery. Memory formation was inferred to be absent if 0 was included in the 95% confidence interval (CI) of the probability. RESULTS The main results showed no evidence of explicit or implicit memory. The 95% CI of the probability of explicit memory formation included 0 for both models, –0.01 (–0.04 to 0.02) and –0.04 (–0.10 to 0.01), respectively. The 95% CI of the probability of implicit memory formation did not include 0 when evaluated using the original model, 0.08 (0.06 to 0.10), but included 0 when evaluated using the extended model, 0.00 (–0.03 to 0.03). The modified Brice interview revealed no evidence of awareness. CONCLUSIONS There was no evidence of explicit or implicit memory formation during remimazolam anaesthesia (BIS 60 to 80). Further research is warranted to establish whether explicit and implicit memories are still absent even in the presence of surgical stimulation. CLINICAL TRIAL REGISTRATION KCT0006752 (http://cris.nih.go.kr)