Retention of auditory information presented during anaesthesia. A study of children who received light general anaesthesia

Implicit memory formation using the word stem completion task during anesthesia in children

AIMS

To determine whether there is evidence of implicit memory formation during pediatric anesthesia using the word stem completion task.

BACKGROUND

In adults, there is mixed evidence for implicit memory formation during anesthesia; however, there is no evidence in children. Implicit memory in adults has been detected using the word stem completion task. This test has not been used in a pediatric anesthetic setting.

METHODS

A total of 200 patients aged 7-12 were randomized to hear one of the two lists of 10 words played continuously while anesthetized. Group 1 heard List A and Group 2 heard List B. Postoperatively, 194 completed a word stem completion task where they were required to complete the stems (the first part of words) corresponding to the words on the two word lists combined, with the first word that came to mind.

RESULTS

Group 1 completed a mean of 2.78 words correctly from List A and a mean of 2.70 words correctly from List B. Group 2 completed a mean of 3.29 words correctly from List A and a mean of 3.66 words correctly from List B. For List A, there was no evidence (P = 0.70) for an association between intraoperative exposure to this list and the odds of successfully completing a stem from this list with the corresponding target word. There was little evidence (P = 0.09) for an association with List B.

CONCLUSION

This study found no strong evidence that children form implicit memories for auditory words during anesthesia. Given the difference between lists, future research is warranted using carefully chosen word stems.

Effects of therapeutic suggestion in children undergoing general anesthesia: a randomized controlled trial

OBJECTIVES AND AIM

The goal of this randomized controlled trial was to examine the effect of intraoperative positive therapeutic suggestion on postoperative nausea and vomiting (PONV) in children undergoing general anesthesia and otolaryngological surgery.

BACKGROUND

Because of the high incidence of PONV following otolaryngological surgery and its negative impact on recovery, researchers have examined various nonpharmacological interventions to target this phenomenon. To date, the effectiveness of therapeutic suggestion has not been studied in children.

METHODS

Participants were 67 children undergoing tonsillectomy and adenoidectomy and their mothers. Children received a standardized anesthetic procedure and were randomly assigned to one of three interventions administered under general anesthesia: therapeutic suggestion, story (prosody control), or standard operating room noise. Children, parents, and healthcare personnel were blinded to group assignment. Nausea and vomiting were recorded in the postanesthesia care unit (PACU) and for the first 3 days at home.

RESULTS

Results demonstrated a decrease in nausea severity across the first 3 days, F(2,49) = 10.37, P < 0.001, but no group differences in nausea severity in the PACU (F(2,49) = 0.87, P = 0.43) or at home (F(2,49) = 0.80, P = 0.46). There were also no group differences in vomiting episodes in the PACU (chi(2) (2) = 1.25, P > 0.05) or at home (F(2,49) = 1.59, P = 0.21).

CONCLUSIONS

In this blinded controlled trial, therapeutic suggestion delivered intraoperatively did not impact children's PONV. However, because this is the first study of this kind, replication may be needed.

Awareness, dreaming and unconscious memory formation during anaesthesia in children

Recent studies have reported an incidence of awareness in children of around 1%, while older studies reported incidences varying from 0% to 5%. Measuring awareness in children requires techniques specifically adapted to a child's cognitive development and variations in incidence may be partly explained by the measures used. The causes and consequences of awareness in children remain poorly defined, though a consistent finding is that many children do not seem distressed by their memories. There are, however, some published reports of persistent psychological symptoms after episodes of childhood awareness. Compared to explicit memory, implicit memory is more robust in young children; however there is no evidence yet for implicit memory formation during anaesthesia in children. Children less than 3 years of age do not form explicit memory, although toddlers, infants and even neonates have signs of consciousness and implicit memory formation. In these very young children the relevance of awareness remains largely unknown.

Awareness During Anesthesia in Children: A Prospective Cohort Study

During routine adult anesthesia, the risk of awareness is 0.1%-0.2%. No recent studies have reported the incidence in children. Altered pharmacology and differing anesthesia techniques suggest that the incidence may differ in children. In this prospective cohort study, we determined the incidence of awareness during anesthesia in children. Eight-hundred-sixty-four children aged 5-12 yr who had undergone general anesthesia at The Royal Children's Hospital were interviewed on 3 occasions to determine the incidence of awareness. The awareness assessment was nested within a larger study of behavior change after anesthesia. Reports of suspected awareness were sent to four independent adjudicators. If they all agreed, a case was classified as true awareness. Twenty-eight reports were generated. There were 7 cases of true awareness, for an incidence of 0.8% (95% confidence interval, 0.3%-1.7%). Only one aware child received neuromuscular blockers, compared with 12% in the nonaware group. No aware child reported distress, and no substantial difference was detected in behavior disturbance between aware (20%) and nonaware (16%) children. The data provide some evidence that, like adults, children are also at risk of intraoperative awareness. Although the cause remains unclear, anesthesiologists should be alerted to the possibility of awareness in children.

Awareness in anaesthesia: incidence, consequences and prevention

Awareness during anaesthesia is a state of consciousness that is revealed by explicit or implicit memory of intraoperative events. Although large clinical surveys indicate an incidence of explicit awareness of < 0.3% during anaesthesia for general surgery, this adverse effect should be a great concern, because patients may be permanently disabled by the experience of being awake during surgery. Prevention of awareness during anaesthesia starts with an appropriate preoperative visit to the patient. The anaesthetic delivery machines must be properly checked before and during anaesthesia. The anaesthetic depth should be assessed by observation of movement responses, and consequently a minimum of muscle relaxants used. Because the anaesthetic depth can be controlled by determination of endtidal drug concentration, volatile inhaled anaesthesia may be associated with a lower frequency of awareness than other anaesthetic regimens.

Motor signs of wakefulness during general anaesthesia with propofol, isoflurane and flunitrazepam/fentanyl and midlatency auditory evoked potentials

Auditory evoked potentials have been used as an indicator of awareness. In the present study we combined epidural analgesia with three techniques of general anaesthesia. Motor signs of intra-operative wakefulness were documented and assessed along with cardiovascular changes and with midlatency auditory evoked potentials. Thirty patients undergoing elective laparotomy were studied as follows: first continuous epidural analgesia was used in all patients to block painful sensation to the level of T5. Intravenous general anaesthesia was induced with propofol (2.5 mg.kg-1 b.w., group 1, n = 10), thiopentone (5 mg.kg-1 b.w., group 2, n = 10) or etomidate (0.2 mg.kg-1 b.w., group 3, n = 10) and maintained with a propofol (3-5 mg.kg-1, group 1), isoflurane (0.4-0.8 Vol%, group 2), flunitrazepam and fentanyl (0.005 mg.kg-1 b.w.) bolus injection every 20 to 30 s (group 3). Heart rate and arterial pressure were recorded continuously. Purposeful movements of the limbs, eye-opening or other movements as well as coughing were documented as motor signs of intra-operative wakefulness. Auditory evoked potentials were recorded in the awake state, after induction and during maintenance of general anaesthesia. Motor signs of intra-operative wakefulness occurred statistically significantly more often in the patients of the flunitrazepam/fentanyl group than in those of the propofol and isoflurane group. There was no correlation between wakefulness and cardiocirculatory parameters. In the awake patients midlatency auditory evoked potentials had high peak to peak amplitudes and a periodic waveform.(ABSTRACT TRUNCATED AT 250 WORDS)

Intra-anesthetic awareness

Awareness during anesthesia is as old as anesthesia itself. Using muscle relaxing drugs, operations can be done on a relaxed but fully aware patient. The problem of intra-anesthetic awareness still exists despite the advances in anesthetic drugs and monitoring. This article reviews the subject from some aspects including its causes, signs, tests and medico-legal points. Awareness during anesthesia can be looked at as 'the invisible scars of surgery.'