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Anesth Analg 2002;95:72-77 © 2002 International Anesthesia Research Society
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Abstract |
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 Top Abstract IntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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We studied the incidence of awareness and explicit recall during general anesthesia in outpatients versus inpatients undergoing surgery. During a 14.5-mo period, we structurally interviewed 1500 outpatients and 2343 inpatients. Among outpatients, there were five cases of awareness and recall (one with clear intraoperative recollections and four with doubtful intraoperative recollections). Of the inpatients, six reported awareness and recall (three with clear and three with doubtful intraoperative recollections). The incidence of clear intraoperative recollections was 0.07% in outpatients and 0.13% in inpatients. The difference in the incidence was not significant. Among outpatients, those with awareness and recall were given smaller doses of sevoflurane than those without awareness and recall (P < 0.05). In conclusion, awareness and recall are rare complications of general anesthesia, and outpatients are not at increased risk for this event compared with inpatients undergoing general anesthesia.
IMPLICATIONS: Rapid recovery from general anesthesia is a crucial element of outpatient surgery. However, this practice may predispose a patient to receive less anesthetic, with increased risk for awareness and recall. We have shown that outpatients undergoing an operation using general anesthesia are not at increased risk for awareness compared with inpatients.
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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During general surgery, awareness and recall appear to be rare complications of general anesthesia, with an incidence of 0.2%–0.4% (1–5). However, in certain patient groups, such as those undergoing anesthesia for cardiac, emergency trauma, or obstetric surgery or bronchoscopy, an increased risk for awareness and recall has been reported (6).
In outpatient surgery, one of the main goals is to conduct operative procedures more effectively and economically than conventionally, i.e., taking patients to the ward before and after the operation. As part of a fluent process (i.e., desire to rapid recovery and fast-tracking), special demands are laid on outpatient anesthesia. Therefore, the patient may receive less anesthetic, with an increased risk for awareness and recall. However, it is not known whether outpatients undergoing surgery are at increased risk for awareness and recall during general anesthesia, because there are no previous studies of this complication in these patients. The aim of this study was to evaluate the incidence of awareness and recall during general anesthesia in outpatients.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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After approval of the hospital ethics committee, we conducted a prospective, open, cross-sectional study of the incidence of awareness and recall during general anesthesia in outpatient surgery. The study was performed between April 1, 1998, and June 15, 1999, in Jorvi Hospital, Espoo, Finland. Jorvi Hospital is a teaching secondary care hospital serving a population of approximately 240,000.
We were interested in patients with explicit recall of a period of general anesthesia (i.e., "intentional or conscious recollection of prior experiences as assessed by test of recall or recognition") (6). (For brevity, only the term "awareness and recall" is used later in reference to awareness and explicit recall.) Outpatients 15 yr or older undergoing surgery using general anesthesia were included in the study. As controls, we used inpatients operated on during the same period under general anesthesia (inpatients were patients who came through a surgical ward before the operation and stayed in the hospital for at least one night after the operation). Patients not speaking Finnish or Swedish and those unable to respond because of their condition (i.e., they were too sick) or who refused to be interviewed were excluded from the study. All patients scheduled for an operation, whether elective or emergency, were included. Cardiac surgery, transplantation, and neurosurgery were not performed in the hospital during the study period. Obstetric and trauma surgery patients were included in the study.
To screen the patients experiencing awareness and recall, we interviewed patients during their stay in the recovery room. Awareness and recall in this study was defined by the ability of the patients to recall any event between the induction of anesthesia and recovery of consciousness at the end of anesthesia. The attending nurse in the recovery room performed the interview. The interview was structured, and the questions were those originally described by Brice et al. (7) and modified by Moerman et al. (8) (Appendix 1). The patients who had recollections from the period of general anesthesia were reinterviewed during the same or following day by one of the authors (JW). To evaluate whether patients with awareness and recall had any prolonged aftereffects (sleep disturbances, anxiety, depression, or preoccupation with death), they were reinterviewed by phone 12–24 mo after the operation.
After screening by the interviewing nurse, any patient suspected to have experienced explicit recall was interviewed by the authors. Patients showing explicit recall were graded into two types: Type 1 was doubtful; patients had unclear memories or dreams that might have been related to intraoperative events. Type 2 was certain; patients had clear, explicit recall of intraoperative events. Patients with possible residual relaxation were included in Type 2 (9). Patients were also questioned about dreaming under general anesthesia, and the dreams were graded as pleasant, neutral, or unpleasant/nightmares. Patients with dreams of hospital staff, diagnosis, medicines, voices in the operation theater, or other possible intraoperative events were considered to belong to the type of doubtful awareness and recall (Type 1).
During the study, 18 anesthesiologists were working in the hospital. They were aware of the continuing study. However, no specific instructions were given to them to standardize or modify their anesthesia methods to avoid awareness and recall.
To estimate the doses of anesthetics used for general anesthesia in our hospital, we reviewed 600 randomly selected anesthesia records. We divided the study period into five phases of 3 mo duration. During each 3-mo period, we collected a random sample of 120 anesthesia records (60 from outpatients and 60 from inpatients). By the end of the study, we had 600 randomly selected anesthesia records from patients without awareness and recall. In addition, we collected the anesthesia records of the patients showing signs of awareness and recall at the interview.
We analyzed the doses of IV anesthetics, opioids, and muscle relaxants in relation to the weight of the patient and the duration of anesthesia. The dose of inhaled anesthetic was calculated as follows: the inspired anesthetic concentration was multiplied by the time (in minutes) this concentration was used. The totals of different concentrations and times were added to a grand total. The result was then divided by the total time of anesthesia (4,10). To estimate the minimum alveolar anesthetic concentration (MAC) values, we divided the total inhaled dose of sevoflurane by 2.05 and that of isoflurane by 1.15 (11).
For statistical analyses, we used the 
2 test as adjusted for the expected infrequency of awareness, i.e., with Yates’ continuity correction, to compare frequencies, and we used Student’s t-test for independent samples. A P value of <0.05 was considered statistically significant. Power analysis was used to estimate the number of patients needed to be interviewed. For this purpose, it was estimated that the incidence of awareness and recall was 0.7% in the group of inpatients (4), and 1500 patients per group would be needed to detect a significant difference if the incidence of awareness and recall were two times higher (i.e., 1.4%) in the group of outpatients. The significance level for the power analysis was 5%, and the power was 90%.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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During the study period we interviewed 1500 outpatients (2 were excluded afterward because they were too young, i.e., <15 yr old) and 2343 inpatients (Table 1). The proportion of interviewed patients was 89% among the outpatients operated on under general anesthesia and 67% among inpatients (P < 0.0001). The reasons for not being interviewed were the following: patients were dropouts because of the busy tempo of inpatient care in the recovery room; there were difficulties with language; the patients were too sick to answer; or they refused to answer.
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Among outpatients, there was one (Patient 1 in Table 2) with a short but clear episode of awareness and recall (Type 2). Four additional patients (Patients 2–5) reported doubtful awareness and recall (Type 1). None of the outpatients reported long-lasting episodes of awareness and recall. Among the inpatients, there were three (Patients 6, 7, and 11) with clear episodes of awareness and recall (Type 2) and three (Patients 8–10) with doubtful awareness and recall (Type 1). The incidence of clear awareness and recall (Type 2) was 0.07% among the outpatients and 0.13% among the inpatients when they were interviewed in the recovery room. The difference in the incidence of awareness and recall between outpatients and inpatients was not significant. In the second interview 12–24 mo after the operation, eight patients (five outpatients [Patients 1–5] and three inpatients [Patients 7, 9, and 11]) with awareness and recall remembered the same perceptions as in the first interview. Three inpatients (Patients 6, 8, and 10) did not have persisting recollections.
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Although all the patients with awareness and recall were women, there was no significant difference in sex distribution (P = 0.08). Neither was any difference found in ASA physical status, body mass index, or age between the patients with awareness and recall and those without it. Only one of the patients (Patient 7) felt pain during surgery (recalled pain during endotracheal intubation). Twenty-two percent of all outpatients reported dreams, which were classified as neutral or pleasant (23% of women and 7% of men; P < 0.001). Among the inpatients, 14% reported pleasant or neutral dreams (15% of women and 12% of men). Nine women (seven inpatients and two outpatients) reported nightmares. None of the men recalled that complication. Among the patients with awareness and recall, two patients, one in both types (Patients 4 and 10 in Table 2), reported sleep disturbances after anesthesia. One of them (Patient 10 in Table 2) was still experiencing nightmares and depression when interviewed 23 mo after the anesthesia. However, subjectively she did not consider any connection between the anesthesia and her symptoms. The other one had sleep disturbances until several weeks after the anesthesia. The descriptions of patients with awareness and recall are given in Table 2.
A wide range of anesthetic drugs was used during the general anesthesias. Among the inpatients, the most frequently used drugs were fentanyl (received by 97% of the patients), thiopental (78%), propofol (25%), isoflurane (76%), sevoflurane (21%), nitrous oxide (71%), rocuronium (58%), and vecuronium (40%). Among the outpatients, the most common drugs were alfentanil (93%), propofol (99%), sevoflurane (49%), nitrous oxide (85%), and rocuronium (12%). Only 19% of the outpatients received muscle relaxants, whereas 97% of the inpatients received relaxants (P < 0.0001). Benzodiazepine premedication (most frequently diazepam) was used more often among the inpatients (88% vs 15%; P < 0.001). In the analyses of the pooled data from in- and outpatients, no difference was found in the incidence of awareness and recall between the patients who had been given benzodiazepine premedication and those who had not. Neither was there any difference within the pooled data in the incidence of awareness and recall between the patients who had received muscle relaxants and those who had not. In outpatients, there was a difference (P < 0.05) between the patients with awareness and recall and those without it in the dosing of sevoflurane (Table 3). However, the doses of inhaled anesthetics (isoflurane and sevoflurane combined) as converted to MAC-equivalents in outpatients and inpatients were not different (MAC-equivalents ± SD were 1.0 ± 0.47 and 0.96 ± 0.38, respectively).
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In inpatients, MAC or end-tidal anesthetic gas values were measured in 59% of cases without and in 50% of cases with awareness and recall. There was no difference in the incidence of awareness and recall between the patients monitored for anesthetic gas concentrations and those not monitored. Among outpatients, anesthetic gas values were not measured in any patient.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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Our results seem to indicate that outpatients are not at increased risk for awareness and recall during general anesthesia compared with inpatients undergoing an operation with general anesthesia. This study was designed to find a significant difference in the incidence of awareness and recall between outpatients and inpatients with the assumption that the incidence would be two times more frequent in the former than in the latter group. Therefore, one cannot definitely exclude the possibility that there is a smaller difference in the incidence of awareness and recall between these groups. However, because contrary to our primary hypothesis, the incidence of awareness and recall appeared to be even smaller (although not significantly) in outpatients than in inpatients, it may be relatively safe to conclude that outpatient surgery does not predispose patients to an increased risk of awareness and recall during anesthesia.
The incidence of awareness and recall in inpatients was smaller than previously reported by us (4) and others (1–3) and was similar to that recently published by Sandin et al. (5). There is no simple explanation for the small incidence of awareness and recall in our study, but in general the incidence of this complication may have decreased (1–5). It is also possible that we have underestimated the true incidence of awareness and recall because we excluded patients unable to respond because of their condition (too sick) or those refusing to be interviewed. In addition, no cardiac surgery was performed in the study hospital. Therefore, the incidence of awareness and recall might have been more frequent if it included patients with an increased risk for complications. Furthermore, the patients were interviewed only once during their stay in the hospital. In their study, Sandin et al. (5) have shown that repeated interviews in the first postoperative weeks may be needed to improve detection of cases with awareness and recall.
In this study, only 15% of outpatients were given benzodiazepine premedication, whereas this medication was given more frequently to the inpatients (i.e., 88%). There was no difference in the incidence of awareness and recall in respect to premedication. This observation seems to agree with the suggestion of a minor role of benzodiazepine premedication in protection from awareness and recall during anesthesia (5). However, any firm conclusion about the effect of benzodiazepines on the incidence of awareness and recall should be drawn cautiously, because the timing of the administration in relation to the operation was not standardized, and the duration of surgery varied considerably. In our study, only 19% of outpatients received muscle relaxants, whereas 97% of the inpatients received relaxants. There was no difference in the incidence of awareness and recall with respect to the administration of muscle relaxants. It is of note that this study was not designed to find significant differences in the incidence of awareness and recall in relation to the administration of benzodiazepines or muscle relaxants, or in the use of anesthetic gas monitoring. Previous studies have shown that awareness and recall without muscle relaxants are extremely rare, and there are only a few reports of this in the literature (12–14). However, in this study there was one outpatient with clear awareness and recall, and there were four additional outpatients with doubtful awareness and recall without muscle relaxants.
In this study, only one inpatient felt pain during anesthesia, and that was caused by endotracheal intubation. This compares favorably with the estimation by Jones (1), who reported that during general anesthesia fewer than 1 of 3000 patients experiences awareness and recall with severe pain. However, 7 of 19 patients in the study of Sandin et al. (5) experienced pain, and Bogetz and Katz (15) reported that 11% of lightly anesthetized patients undergoing surgery for major trauma experienced pain during surgery. Auditory sensations were the most common type of perception in our study. Three of five outpatients and two of six inpatients with awareness and recall heard sounds or voices. The result is similar to the study of Schwender et al. (16). In their study, all patients with awareness and recall mentioned auditory perceptions (hearing sounds or voices). That is not surprising because hearing is considered to be the first sensory function to return with lightening of anesthesia (17).
Grading awareness and recall is a complicated task (6). In clear cases of intraoperative awareness with recall, there are no problems in deciding whether or not the patient has been conscious during the anesthesia and recalls intraoperative events. The decision is much more difficult with a patient who has confusing memories or dreams possibly related to intraoperative events. Therefore, in this study we classified awareness and recall into two types: doubtful and clear. Because of the difficulty in definition of awareness and recall, we also think that patients with confusing memories or dreams should be reported because we cannot eliminate the possibility that they are related to intraoperative events. However, in the incidences of awareness and recall, we included only patients graded as Type 2, i.e., clear episodes of awareness.
The proportion of interviewed patients was 89% among outpatients but only 67% among inpatients. However, it is likely that the proportion of interviewed patients, as well as the absolute number (n = 3843), is large enough and representative enough of the hospital patient population not to cause any major sample bias.
Contrary to our hypothesis, it appeared that dosing of anesthetics was similar during in- and outpatient surgery. After isoflurane and sevoflurane were converted to MAC-equivalents, no significant difference in the dosing of inhaled anesthetics between outpatients and inpatients was found. In the group of outpatients, those with awareness and recall received smaller doses of sevoflurane during the maintenance of their general anesthesia than those without awareness and recall. Because of the small incidence of awareness and recall, one should consider very cautiously the statistical difference in the dosing of anesthetics between the patients with and without awareness and recall. Further, no difference in the dose of isoflurane, the main volatile anesthetic in inpatients, was observed between the patients with and without awareness and recall. Nevertheless, our finding with sevoflurane may indicate that smaller dosing of anesthetics is a major factor in predisposing patients to awareness and recall.
In conclusion, patients undergoing outpatient surgery using general anesthesia are not at increased risk for awareness and recall than patients operated on using general anesthesia as inpatients. Although the incidence of awareness and recall was small in this study, and may be in further decline, the complication still exists.
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Appendix 1: Questions Asked During the Interviews |
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TopAbstractIntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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Questions asked of all patients:
- What is the last thing you remember before going to sleep for your operation?
- What is the first thing you remember on waking after your operation?
- Do you remember anything in between?
- Did you have any dreams?
- What was the most unpleasant thing you remember from your operation and anesthesia?
Additional questions asked of patients who reported awareness:
- What did you notice: sounds, tactile sensations, visual perception, pain, paralysis?
- Did you feel something in your mouth or throat?
- What went through your mind?
- Did you believe you were dreaming?
- How long did it last?
- Did you try to alert anyone?
- How was your preoperative mental state?
- Have there been any consequences of awareness?
- Did you inform hospital staff?
- Have you changed your opinion about anes-thesia?
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References |
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TopAbstractIntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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- Jones JG. Perception and memory during general anesthesia. Br J Anaesth 1994; 73: 31–7.
[Free Full Text] - Liu WH, Thorp TA, Graham SG, Aitkenhead AR. Incidence of awareness with recall during general anesthesia. Anaesthesia 1991; 46: 435–7.[Web of Science][Medline]
- Nordström O, Engström AM, Persson S, Sandin R. Incidence of awareness in total i.v. anaesthesia based on propofol, alfentanil and neuromuscular blockade. Acta Anaesthesiol Scand 1997; 41: 978–84.[Web of Science][Medline]
- Ranta SOV, Laurila R, Saario J, et al. Awareness with recall during general anesthesia: incidence and risk factors. Anesth Analg 1998; 86: 1084–9.[Abstract]
- Sandin R, Enlund G, Samuelsson P, Lennmarken C. Awareness during anaesthesia: a prospective case study. Lancet 2000; 355: 707–11.[Web of Science][Medline]
- Ghoneim MM, Block RI. Learning and consciousness during general anesthesia: an update. Anesthesiology 1997; 87: 387–410.[Web of Science][Medline]
- Brice DD, Hetherington RR, Utting JE. A simple study of awareness and dreaming during anaesthesia. Br J Anaesth 1970; 42: 535–42.
[Abstract/Free Full Text] - Moerman N, Bonke B, Oosting J. Awareness and recall during general anesthesia: facts and feelings. Anesthesiology 1993; 79: 454–64.[Web of Science][Medline]
- Ho AM. Awareness and recall during emergence from general anaesthesia. Eur J Anaesthesiol 2001; 18: 623–5.[Web of Science][Medline]
- Ranta SOV, Jussila J, Hynynen M. Recall of awareness during cardiac anaesthesia: influence of feedback information to the anaesthesiologist. Acta Anaesthesiol Scand 1996; 40: 554–60.[Web of Science][Medline]
- Koblin DD. Mechanisms of action. In: Miller RD, ed. Anesthesia. 5th ed. New York: Churchill Livingstone, 2000: 48.
- Cundy JM. Post traumatic stress disorders. Br J Anaesth 1995; 75: 501–2.
[Free Full Text] - Saucier N, Walts LF, Moreland JR. Patient awareness during nitrous oxide, oxygen and halothane anesthesia. Anesth Analg 1983; 62: 239–40.
[Free Full Text] - McLeskey CH. Awareness during anesthesia. Can J Anaesth 1999; 46: R80–3.[Web of Science][Medline]
- Bogetz M, Katz J. Recall of surgery for major trauma. Anesthesiology 1984; 61: 6–9.[Web of Science][Medline]
- Schwender D, Kunze-Kronawitter H, Dietrich P, et al. Conscious awareness during general anaesthesia: patients’ perceptions, emotions, cognition and reactions. Br J Anaesth 1998; 80: 133–9.
[Abstract/Free Full Text] - Trustman R, Dubovsky S, Titley R. Auditory perception during general anesthesia: myth or fact? Int J Clin Exp Hypn 1977; 25: 88–105.[Web of Science][Medline]
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