Awareness, or the unwanted recall of intraoperative events during general anesthesia (GA), is an infrequent anesthetic complication that may pose the risk for adverse psychological consequences. Several large prospective studies have reported a 0.1%–0.2% incidence of awareness in adults,1–4 and as many as 50% of these may go on to experience mental distress including symptoms of posttraumatic stress disorder.5,6 Until recently, limited data were available regarding the incidence and consequences of awareness in children. Three recent studies, however, evaluated awareness using semistructured interviews modified for use in children and reported incidences between 0.6% and 2.7%.7–9 The more frequent occurrence of awareness in these studies was attributed to the altered and interindividual differences in anesthetic pharmacology in children and differences in the practice of pediatric anesthesia. Additionally, two studies recently tested explicit memory in children using recordings of animal sounds or words played at specific times during GA and found that 0.2%–1.1% of children experienced awareness.10,11 Discrepancies in the reported incidences from these single-site pediatric studies may be due, in part, to differences in anesthetic techniques, interviewing methods, and definitions of awareness between the studies. Given such differences, replication studies are warranted to examine intraoperative awareness, factors that contribute, and psychological consequences of this important phenomenon in children.
The purpose of this prospective, observational study was to evaluate the incidence of awareness during routine GA practice in a cohort of children from several settings in the United States. The secondary objectives of this study were to identify factors contributing to intraoperative recall and to describe its short-term psychological effects in children.
This study was approved by the IRBs at the University of Michigan, University of Colorado, and Emory University. Parent consent and child assent were obtained from all subjects who took part in this study. The study included a nonprobability, consecutively recruited sample of children who met the following criteria: English-speaking, aged 5–15 yr, ASA physical status I–IV, and undergoing GA for an elective surgical procedure scheduled to last 30 min or more. Children were excluded if they had a known condition (e.g., cognitive or psychological disorder, prolonged postoperative mechanical ventilation) preventing them from responding accurately or adequately to postoperative interviewing. Additionally, children who underwent surgery during the past 6 mo or who were scheduled to undergo a second procedure during the course of interviews were excluded.
All children received perioperative and anesthetic care and monitoring per routine practice at the discretion of their care providers. Induction rooms were not used at any of the sites. The anesthesiologists knew that a study of awareness was being conducted but were not specifically informed when their patients were enrolled. The following data were collected: demographics, pertinent history, surgery type and duration, anesthetics used and perioperative medications administered, details regarding airway management, and recovery characteristics. Nurses in the recovery room scored the child's agitation behavior (i.e., none, mild, moderate, or severe) and pain (using the Bieri Faces scale) on emergence and 30 min later.
Children were interviewed either face-to-face or by telephone on postoperative days 1, 3 (±1), and 14 (±2) using a semistructured Brice questionnaire12 that was modified for children by simplifying the language and use of open-ended questions only with the intention of minimizing false positive responses. Data from a pilot group of 25 children were used to review and examine the procedure, assessment tools, and questionnaire, and to make modifications in the tools as deemed necessary. The final questionnaire is presented in the Appendix. Before study initiation, primary investigators (PIs) and all study personnel underwent specific training via video/teleconference by a psychologist regarding interview methodology to ensure consistency across sites. Interviews were then conducted by these trained assistants, nurses, or psychologists in all cases. Questions were read verbatim (from the interview sheets) for each child in the study. Questions were restated or reworded for children who did not answer or understand the question in order to prompt an answer, but without leading the child in any way. If a child did not respond to a question after the second prompting, a response of “no answer” was recorded and the interviewer proceeded to the next question.
The PI at each site was responsible for reviewing the child's responses to the question, “Do you remember anything between falling asleep and waking up?” If the child's response was deemed as potential awareness, the PI reviewed the anesthetic course and discussed the recollections with the child's anesthesia and surgical providers to confirm or refute the memories. After this discussion, the PI coded the recollection as follows: No awareness, Dreaming, Possible Awareness, Probable Awareness, or Definite Awareness (see definitions, Table 1). In all cases of awareness, the child's anesthesiologist or PI telephoned the child's parent/guardian to discuss the anesthesia and recovery experience and offer the option for psychological follow-up for the child. Additionally, these cases of awareness were later discussed by the three PIs across study sites, and an internal consensus was reached regarding possible/probable awareness. Finally, the details of these cases and interviews and those of a randomly selected sample of cases classified as “no awareness” or “dreaming” were later reviewed by three external, pediatric anesthesiologists who similarly coded the recollections. The external reviewers had no information regarding the conduct of the anesthetic or the timing of events. Additionally, the external reviewers were unable to confirm the child's recollections with the surgical team. For the purpose of this study, possible/probable awareness was defined as cases with agreement between the internal consensus and at least two of the three external reviewers.
The sample size was determined a priori using an estimated population prevalence technique13 based on data derived from adult and pediatric studies. The sample calculation determined that a minimum of 1799 children was needed to demonstrate an incidence of at least 0.3% (99% confidence), believed to be a conservative estimate of the incidence of awareness in children. Sampling continued beyond this number to ensure complete data and follow-up in a sufficient number of children.
Descriptive statistics were used to examine the incidence of awareness in children and its related outcomes. Nonparametric comparisons were used to examine factors associated with possible or probable awareness. P values <0.05 were accepted as statistically significant.
One thousand eight hundred thirty children were recruited. Of these, 1187 (65%) completed all three interviews, 453 (25%) completed two, 148 (8%) completed one, and 42 (2%) completed none. Additionally, three children who were interviewed did not provide enough information to allow the PI to classify awareness, and in one case, the anesthetic plan changed to sedation only. The final sample included data from 1784 children who completed at least one interview. A description of the sample is presented in Table 2.
One thousand five hundred fifty-four (87.1%) children reported no memories or dreaming between falling asleep for surgery and waking up. One hundred thirty-five children (7.4%) answered “yes” to the question, “Do you remember anything between falling asleep and waking up?” Two hundred (11.2%) children reported dreaming during surgery. Thirty-two cases were coded as possible or probable awareness by at least one entity (i.e., either the internal consensus or one of the external reviewers). These cases are described in Table 3. However, only 14 of these cases met the definition for possible/probable awareness (i.e., agreement between the internal consensus and at least two external reviewers), making the incidence 0.8%. In only one case, there was agreement among all reviewers. There was no significant difference in the incidence of awareness among sites (Michigan 0.8%, Colorado 0.6%, and Emory 1.5%).
Data related to the psychological impact of the perioperative recollections are presented in Table 3. Six of the 14 children with awareness (43%) remembered feeling scared during their surgery and three (21%) reported hurting. Two children in this group (14%) said they would feel worse if they had to have surgery again, seven (50%) would feel the same or better, and five (36%) reported different feelings during different interviews. These reports were not significantly different from reports of children with no recall (260 [15%] worse, 1128 [64%] neutral or better, and 377 [21%] different feelings). Parents of children with awareness refused psychological follow-up for their child in all cases. Additionally, there were no significant differences between children with awareness and those with no awareness in relation to postoperative highest pain scores (1.8 ± 1.7 vs 2.7 ± 3.1, respectively) or presence of agitation (2 [14%] vs 221 [13%]).
Data were analyzed for potential associations between multiple child and perioperative factors and the outcome, possible/probable awareness (Table 4). The only factor that was significantly associated with awareness was endoscopic procedure. Only 27 children in this study, all from the University of Colorado, were monitored with the bispectral index during their procedure. None of these children experienced awareness; however, the small sample of children in this group precludes comparisons with other children.
A recent sentinel event alert issued by the Joint Commission emphasized the importance of intraoperative awareness, stating that this problem is underrecognized and undertreated. Awareness may be particularly underrecognized in children who may be reluctant or unable to describe their intraoperative memories. This study provides the first data regarding the incidence of awareness in children across pediatric settings in the United States. In this sample, 0.8% of children experienced possible or probable intraoperative awareness. Although the specific recollections appeared to be innocuous, 43% of these children reported feeling scared and 21% hurting during their surgery. Psychological follow-up was deemed unnecessary in all cases, and none of the children or parents expressed concern. Additionally, 14% of children with possible/probable awareness stated they would feel worse if they had to undergo another anesthetic procedure in the future. This finding was similar to reports from children who did not experience awareness (15% would feel worse). These findings suggest that awareness did not cause undue psychological distress in this sample.
There is considerable variability in the reported incidence of awareness in pediatric studies.7–11 Discrepancies in such reporting may be due in part to the difficulty in reaching agreement regarding what constitutes awareness or recall. Indeed, our findings suggest that the incidence of awareness could range from 0.06% given the most stringent of definitions (i.e., agreement between all individuals) to 1.8% given the most liberal (i.e., coded by one individual).
The differences in questionnaires and interviewing methods among studies may have further influenced the reports obtained from children. It has been suggested that administering a structured questionnaire may produce an increase in reported cases of awareness.14 Children, in particular, may be more suggestible and more likely to report memories especially on repeated questioning. In our study and in a recent study by Davidson et al.,10 7% of children stated that they remembered something during surgery. However, <1% of these children were able to describe memories that were considered to be awareness. Davidson et al. suggested that children have a diminished ability to “encode and consolidate memory” making it difficult to differentiate true memories in this population.
Several studies in adults have identified populations at greater risk for awareness during anesthesia. Adults undergoing cesarean delivery, cardiopulmonary bypass, and surgery for major trauma have been reported to have a high incidence of this outcome.15–17 Additionally, higher ASA physical status,2 use of neuromuscular blocking drugs,3 and small doses of the primary anesthetic4 have been associated with the occurrence of awareness in adults. Lopez et al.8 identified multiple intubation attempts as a predictor for awareness in children. In our study, endoscopic procedure was the only factor found to pose a higher risk for awareness. It could be speculated that lighter planes of anesthesia may contribute to awareness in such cases with short times from induction of anesthesia to onset of the procedure. However, data regarding anesthetic concentrations were not recorded for the purposes of this study. The studies in children are likely underpowered to identify other potential risk factors for this rare outcome.
Adults who experienced awareness in previous studies frequently reported negative feelings including helplessness, fear, terror, and desperation.1,6,18 However, a prospective study found no differences in anxiety or depression scores 30 days after surgery between adults who experienced awareness compared with those who did not.1 Long-term follow-up studies of adults with awareness found between 2% and 50% exhibited symptoms of posttraumatic stress disorder.5,6,18 The large variability in these findings was likely the result of a selection bias related to the recruitment methods.
Data in children, including those from the present study, describe only 1 of 45 children with awareness that required short-term psychological referral.7–10 Additionally, a recent follow-up study by Lopez et al.19 reported no children with long-term psychological symptoms after intraoperative awareness. Although these data are somewhat reassuring, it must be noted that only 7 of the 11 children with awareness were interviewed in the study by Lopez et al. This may have introduced a selection bias similar to studies in adults. Previous investigators have speculated that differences in intraoperative sensations, levels of understanding, and perspectives regarding the relevance of awareness may explain, in part, differences in psychological outcomes between adults and children.19,20 Follow-up data in a larger sample of children with awareness are needed to further our understanding of the psychological impact of awareness.
Several limitations are posed by studies of this nature, potentially confounding the interpretation of results. It is possible that children may be unable to separate events occurring preoperatively, during induction or recovery from those occurring during the procedure, thereby inflating the incidence of intraoperative awareness in this and previous studies. This possibility is evident in several of the specific memories in subjects from this and previous studies. These subjects appear to have memories that describe events during induction or during the postoperative period. The difficulty with temporal organization of memory in children was underscored by Davidson et al.,10 who found that four children reported hearing train sounds during surgery when these sounds were actually played preoperatively. Although the structured interview used in this study posed questions in a chronologic manner in an attempt to minimize this possibility, difficulties with temporal context cannot be dismissed. Another concern, as mentioned above, is that children may be particularly suggestible during interviews, thereby affecting the reliability of their responses. This effect was minimized by our standardized prestudy training of all interviewers and by including only open-ended and nonleading questions in the interview. The reliability of the child's recollections was supported in part by confirmation between the principal investigator and the child's care providers who were present during the procedure.
This multicenter trial found that 0.8% of children undergoing GA had possible or probable awareness of intraoperative events. Children undergoing an endoscopic procedure were more likely to experience awareness compared with those undergoing other procedures. Although a significant number of children reported hurting or being scared during the procedure, they were no more likely than those without awareness to be worried if they were to require subsequent surgery. These data suggest that children with awareness did not develop short-term mental distress; however, further follow-up of these children is needed to exclude long-term psychological impact. This study confirms previous reports that awareness under GA can occur in children. Furthermore, a child's report of intraoperative recall should not be readily dismissed but addressed with appropriate follow-up.
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