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*Department of Anesthesia and Intensive Care Medicine, Helsinki University Central Hospital, Children’s Hospital, Helsinki, Finland; and Department of Anesthesia and Intensive Care, Helsinki University Central Hospital, Jorvi Hospital, Espoo, Finland
Address correspondence and reprint requests to Johanna Wennervirta, MD, Department of Anesthesia and Intensive Care Medicine, Children’s Hospital, Helsinki University Central Hospital, Stenbäckinkatu 11, FIN-00290 Helsinki, Finland. Address e-mail to johanna.wennervirta{at}hus.fi
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Abstract |
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 Top Abstract IntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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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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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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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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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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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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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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Additional questions asked of patients who reported awareness:
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References |
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TopAbstractIntroductionMethodsResultsDiscussionAppendix 1: Questions Asked...References |
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