Memory formation during anaesthesia: plausibility of a neurophysiological basis

Immediate retrograde amnesia induced by midazolam: A prospective, non-randomised cohort study

BACKGROUND

Midazolam, a short-acting benzodiazepine, has sedative, anxiolytic, amnestic and anticonvulsant effects. Given its advantages of rapid onset, short duration and low toxicity, midazolam is optimal for any procedural sedation. Midazolam is known to cause anterograde amnesia; however, the possibility of retrograde amnesia has also been raised. This prospective cohort, non-randomised study evaluated the presence and extent of retrograde amnesia induced by midazolam during caesarean delivery.

METHODS

One hundred parturients scheduled for elective caesarean delivery under spinal anaesthesia were enrolled. As soon as giving birth, six picture cards were shown to the patients in 1-min intervals, and then midazolam (0.1 mg/kg) was given or not according to the patients' preference. This overall retrograde recall rate of six cards was the primary outcome of our study, which was asked by a blinded investigator.

RESULTS

The overall retrograde card recall rate was lower in the midazolam group compared with the control group (77.0 ± 13.4 vs. 87.7 ± 3.9%, P < .001), especially at 1 minute before midazolam administration (58% vs. 88%, P < .001). Decreased memory trend was observed as time progressed towards midazolam administration in the midazolam group (P = .035). More patients answered 'yes' to the factitious event in the midazolam group than in the control group (26% vs. 4%, P = .004).

CONCLUSION

Intravenous midazolam could cause a brief-period retrograde amnesia in visual and event memory. Moreover, there were more spurious reports of intraoperative factitious events in the midazolam group, implying that episodic memories were also affected by midazolam.

Propofol and sevoflurane affect intra-operative memory formation of words differently: A prospective cohort study

BACKGROUND

Memory priming seems possible even during apparently adequate anaesthesia. However, the effects of different anaesthetics and type of stimuli, by virtue of their specific neural underpinnings, have not been considered.

OBJECTIVE

To determine if intra-operative implicit memory is affected by the type of anaesthesia (propofol or sevoflurane) or by the type of stimuli (abstract or concrete words).

DESIGN

Two consecutive, randomised controlled experiments.

SETTING

Neurological institute in Milan, Italy.

PATIENTS

Forty-three patients undergoing anaesthesia with propofol (experiment 1) and 32 patients undergoing anaesthesia with sevoflurane (experiment 2). Patients were ASA I or II, age 18 to 65 years, native Italian speakers, right-handed and without any condition affecting memory or hearing.

INTERVENTION

During anaesthesia, the patients heard a list of either concrete or abstract words or no words at all (controls). Explicit memory was tested with an explicit recall task and the Brice Interview; implicit memory was assessed through a word stem completion test.

OUTCOME MEASURES

The number of explicitly recalled words, positivity to the Brice Interview, the proportion of target and nontarget hits, and a derived implicit memory score.

RESULTS

With propofol, the proportion of target hits was significantly greater than the proportion of nontarget hits for the concrete word experimental group (P = 0.018). The implicit memory score of the concrete word experimental group was significantly higher than the score of both the abstract word experimental group (P  = 0.000) and the concrete word control group (P = 0.023). With sevoflurane, the proportion of target hits was significantly higher than the proportion of nontarget hits for the abstract word experimental group only (P = 0.027). No patients had a BIS above 60 and no one could recall intra-operative events or words.

CONCLUSION

Intra-operative memory for words can form during apparently adequate BIS-guided anaesthesia but is modified by propofol or sevoflurane acting on different brain targets. Further studies on larger samples and using neuroimaging techniques are needed.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT03727464.

Awareness during emergence from anesthesia: Features and future research directions

The anesthesia awareness with recall (AAWR) phenomenon represents a complication of general anesthesia consisting of memorization of intraoperative events reported by the patient immediately after the end of surgery or at a variable distance from it. Approximately 20% of AAWR cases occur during emergence from anesthesia. Clinically, these unexpected experiences are often associated with distress especially due to a sense of paralysis. Indeed, although AAWR at the emergence has multiple causes, in the majority of cases the complication develops when the anesthesia plan is too early lightened at the end of anesthesia and there is a lack of use, or misuse, of neuromuscular monitoring with improper management of the neuromuscular block. Because the distress caused by the sense of paralysis represents an important predictor for the development of severe psychological complications, the knowledge of the phenomenon, and the possible strategies for its prophylaxis are aspects of considerable importance. Nevertheless, a limited percentage of episodes of AAWR cannot be prevented. This paradox holds also during the emergence phase of anesthesia which represents a very complex neurophysiological process with many aspects yet to be clarified.

Complexities of human memory: relevance to anaesthetic practice

Mechanisms of anaesthetic actions on memory have largely focused on easily definable aspects of episodic memory, with emphasis on particular drug interactions on specific memory processes. However, the memory landscape of the perioperative experience includes many facets that lie outside these conceptualisations. These include patient recall of preoperative conversations, patient beliefs regarding allergies and unusual/uncommon anaesthetic events, memories of awareness, and particularly vivid dreams during anaesthesia. In no small part, memories are influenced by a patient's interpretations of events in light of their own belief systems. From the practitioner's point of view, relating fully to the patient's experience requires some framework of understanding. The purpose of this review is to highlight research over the previous decades on belief systems and their interactions with autobiographical memory, which organises episodic memories into a personally relevant narrative. As a result, memory is a set of continuously malleable processes, and is best described as a (re)constructive rather than photographic instantiation. Belief systems are separate but closely interacting processes with autobiographical memory. The interaction of a constantly evolving set of memories with belief systems can explain phenomena such as illusions, distortions, and (re)constructions of factitious events. How anaesthetics and our patient interactions influence these behaviours, and vice versa, will be important questions to explore and define with future research.

Consciousness fluctuation during general anesthesia: a theoretical approach to anesthesia awareness and memory modulation

With anesthesia awareness as a model of study we debate the both fascinating and dangerous phenomenon called consciousness fluctuation that takes place during surgical anesthesia. In accordance with current scientific knowledge this paradox is the consequence of our limits in both precise knowledge of anesthesia mechanisms and our inability to accurately assess the level of anesthesia with brain monitoring. We also focus on the relationships between memory and anesthesia, as well as the possibility of interfering with memory during general anesthesia.