Awareness during general anesthesia can cause late psychological symptoms. Selection bias may have affected the results in previous retrospective studies. The authors used prospective consecutive collection to recruit patients with previous awareness.


In a cohort of 2,681 consecutive patients scheduled to undergo general anesthesia, 98 considered themselves to have been aware during previous surgery. Six patients died before inclusion, and another 13 were excluded (4 cases of stroke or dementia, 7 declined to participate, and 2 could not be located). Seventy-nine patients were interviewed by telephone, and medical records were checked in uncertain cases. The interview followed a structured protocol, including seven late symptoms (anxiety, chronic fear, nightmares, flashbacks, indifference, loneliness, and lack of confidence in future life). Three persons independently assessed the interviews for classification, to determine whether awareness had occurred.


Four cases were performed using regional anesthesia, and another 29 were not considered as awareness by the assessors. Therefore, the final analyses included 46 patients. Twenty (43%) had experienced pain, and 30 (65%) described acute emotional reactions during the awareness episode. Fifteen (33%) patients had experienced late psychological symptoms afterward. In 6 of those cases, the symptoms lasted for more than 2 months, and 1 patient had a diagnosis of post-traumatic stress disorder. Acute emotional reactions were significantly related to late psychological symptoms (P<0.05).


The method for recruiting awareness cases in studies on late psychological symptoms may affect the result. The authors found fewer and milder problems, despite a similar degree of initial problems as in previous studies.

AWARENESS with explicit recall during general anesthesia causes dissatisfaction,1discomfort, and also long-term psychological symptoms.2–5The first study on awareness, published in 1961, found an incidence of 1.2%.6Since then, the incidence of awareness has decreased, with a reported incidence during the past 15 yr of between 0.1% and 0.4%.1,7–11Two recent studies concluded that the incidence of awareness may be decreased by 80% if the Bispectral Index were used.12,13Nevertheless, the large number of patients given general anesthesia will generate a considerable number of awareness cases every year.

Late psychological symptoms after awareness were described in 1961.14Since then, post–traumatic stress disorder (PTSD) has been defined and identified as a complication of awareness.2To date, five studies that address the incidence of late psychological symptoms after awareness have been published. Four of those were retrospective, and the only prospective study included no more than nine interviews.2–5,15These studies reported a high incidence of late psychological symptoms (range, 39–84%), and in one study, 56% of patients developed PTSD, although the definition of symptoms and diagnoses in these studies were not uniform. Because awareness cases are difficult to find, advertising, referral, and closed claims analyses have been used for retrospective inclusion. However, these methods for recruiting patients may have allowed for selection bias in previous retrospective studies and led to biased outcomes. Avoidance or lack of interest to participate may have resulted in missed cases, or alternately, it may have resulted in overrecruiting of dissatisfied patients and those who seek economic benefit.

To minimize selection bias, we used a prospective consecutive interview after surgery, to recruit patients who considered themselves to have experienced awareness during any previous anesthesia. The aim of the study was to assess the incidence and general severity of immediate and delayed problems due to awareness.


Two thousand six hundred eighty-one consecutive patients, from January 2001 to May 2002, who had undergone general anesthesia 1–3 days earlier, were interviewed according to Brice et al.  16One additional question was added to the interview: whether they had experienced awareness earlier in life. Ninety-eight patients (3.7%) considered themselves as having been aware during previous general anesthesia. These patients were considered eligible for further exploring about long-term consequences of awareness. The study was ethically approved by the institutional review board at Linköping University, Linköping, Sweden.

Six patients died before inclusion. A letter with information, including content and arrangement of the interview, was sent to the remaining 92 patients. Of these, 4 were excluded because of stroke or dementia, 7 declined to participate, and 2 patients could not be reached. Therefore, 79 patients were interviewed by telephone after informed consent.


The duration of each telephone interview was approximately 45 min. A structured protocol divided into seven sections, similar to that of Schwender et al. ,5was used. The different sections were personal data, detailed own description of the awareness episode, sensory perception, acute emotions and cognition during the awareness episode, late psychological symptoms afterward, and handling of the knowledge of having been aware. Each section was subdivided (table 1). In uncertain cases, medical records were obtained, if possible, and checked.

Table 1. Interview Structure 

Table 1. Interview Structure 
Table 1. Interview Structure 

Data Analysis and Statistics

Three coworkers with experience from awareness studies independently assessed the interviews for awareness classification. The classification decision was unanimous in all cases but three. In those three cases, a 2 to 1 majority was considered as awareness after discussion. The outcome measures for the parameters were either yes or no responses, except for three. The three parameters measuring acute emotions, the seven measuring late psychological symptoms, and the pain parameter were also semiquantified: 0 = none, 1 = light to moderate, and 2 = severe. This gives a maximum total severity score of 6 for acute emotions and 14 for late psychological symptoms (table 1). Acute emotions and late psychological symptoms were also classified as no (total score = 0) and yes (total score = 1–14). Because of the small numbers, logistic regression was not considered appropriate. The Fisher exact test (two-tailed) was used on parameters considered as interesting in advance, namely: sex, relaxant anesthesia, pain during surgery, acute emotions during the awareness episode, and late psychological symptoms.

Patient Characteristics

Four of the 79 possible cases were performed using regional anesthesia. Another 29 patient stories were not considered as awareness by the three assessors (table 2). These experiences included perioperative nightmares, memories before or after surgery, and recollections too diffuse for awareness classification. Therefore, the final analysis included 46 awareness cases (table 3).

Table 2. Patients Classified as Not Being Awareness Cases 

Table 2. Patients Classified as Not Being Awareness Cases 
Table 2. Patients Classified as Not Being Awareness Cases 

Table 3. Patients Classified as Awareness Cases 

Table 3. Patients Classified as Awareness Cases 
Table 3. Patients Classified as Awareness Cases 

Personal Data

There were 14 men and 32 women. The mean age when the awareness episode occurred was 31 yr (range, 6–62 yr). Five patients were children at the time of awareness (age < 18 yr). The median awareness year was 1980 (range, 1935–2001). Three patients had experienced awareness on more than one occasion. Muscle relaxants had been used in at least 35 cases (76%). In another 4 older cases, where medical records could not be found, the use of muscle relaxants could not be confirmed. Eleven patients considered themselves as having been nervous before the operation.

Sensory Perception during the Awareness Episode

Auditory (n = 33; 70%) and tactile (n = 32; 72%) perceptions were the most common. Twenty patients (46%) had experienced pain, and 14 scored their pain as severe. Seventeen patients had felt paralyzed, and another 12 were not able to tell because they had not tried to move. Visual memories were described in 18 cases (39%). All patients had some kind of sensory perception.

Acute Emotions during the Awareness Episode

Twenty-six patients experienced helplessness (15 severe and 11 moderate). Acute fear was expressed in 25 cases (15 severe and 10 moderate), whereas panic was disclosed by 20 patients (17 severe and 3 moderate). In total, 30 patients (65%) stated they had experienced an acute emotional reaction (table 3).

Cognition during the Awareness Episode

Thirty-seven patients claimed that they had understood what was going on, and 31 had tried to communicate. Eight patients had delayed understanding that they had been aware (range, 1 day to 2 yr).

Late Psychological Symptoms Afterward

Thirty-one patients denied any late symptom at all (total score 0). In the remaining 15 cases (33%), three of the seven classified late symptoms dominated. These were nightmares (n = 11), anxiety (n = 10), and flashbacks (n = 9) (table 4). The median total severity score was 4 (range, 1–12). Only 8 patients (17%) had a total score above 2. Nightmares and flashbacks accounted for 34 of total 59 points from late symptoms. No obvious trend indicating that the severity of late psychological symptoms after awareness has changed over the years studied was identified. The duration of late symptoms varied, and in 9 patients, they faded within 2 months. In 6 patients, the symptoms persisted for years, albeit in 4 of those patients, the symptoms were restricted to nightmares and flashbacks. The remaining 2 patients had more severe mental problems (total scores of 12 and 10, respectively) and underwent psychiatric care.

Table 4. Awareness Patients with Any Late Mental Symptom 

Table 4. Awareness Patients with Any Late Mental Symptom 
Table 4. Awareness Patients with Any Late Mental Symptom 

Handling of the Knowledge of Having Been Aware

Thirty-nine patients had told someone about their awareness experience, often family and relatives, but 23 also told the medical staff (surgeon, anesthetist, or nurse). Thirteen of the 39 patients who described their awareness experiences were greeted with skepticism. During subsequent surgeries, 19 patients (41%) reported a lack of trust in medical staff, but only 4 (9%) had kept this attitude before their most recent surgery. Four patients had contacted medical help because of mental illness. The first had a diagnosis of PTSD. She had been exposed to extreme mental stress earlier in her life. Apart from experiences from two military battles, she had also been raped. The second had a diagnosis of schizophrenia. She was referred from the surgical ward to closed psychiatric care because of psychosis after the gallbladder operation during which she was aware. It is worth noting that she had not told anyone about her awareness experience before she was identified in our study. The third patient had a panic disorder, and the diagnosis of the fourth case was unclear.

Relations between Outcome Parameters

Acute emotions during the awareness episode, but not sex, pain, or relaxant anesthesia, were significantly related to late psychological symptoms (P < 0.05).

In consecutive patients presenting for surgery, we found a smaller proportion of patients with late psychological symptoms after awareness, as compared with previous investigations using other methods for inclusion (table 5). Thirty-three percent of our patients scored at least one point in late symptoms (table 4). In 9 of those 15 cases, the symptoms disappeared within 2 months, whereas the remaining 6 patients had symptoms for years, which is worth taking into consideration. In 4 of these 6 patients, nightmares and flashbacks were the only remaining symptoms. These were insufficient for a diagnosis of PTSD. Two patients with persistent symptoms had contacted psychiatric care. One of these patients had been diagnosed with PTSD, and the other had been diagnosed with schizophrenia. We do not know of any data suggesting that awareness can cause schizophrenia. Although two of our cases developed severe mental problems after their episodes of awareness, it is far from clear that their psychiatric diagnoses can be attributed to the awareness episodes.

Table 5. Studies on Late Psychological Symptoms after Awareness 

Table 5. Studies on Late Psychological Symptoms after Awareness 
Table 5. Studies on Late Psychological Symptoms after Awareness 

Sixty-five percent of the patients had reacted emotionally in the operating room; an experience suggested as constituting a risk for late psychological symptoms.5,15Because our incidence of immediate emotional reactions is at least at the same level as in previous studies, this cannot explain our lower incidence of late psychological symptoms. Among the examined parameters in our study, only acute emotional reactions were statistically related to late psychological symptoms.

The most probable explanation for our low incidence of late psychological symptoms, and the relatively less pronounced severity, is the method by which we identified this study population. Prospective identification of awareness patients is laborious. Of the published studies on symptoms after awareness, only one small study was prospective.15Previous retrospective studies have used advertisement, referral, and closed claims analysis for assessing late psychological symptoms.2–5Advertisement may mainly appeal to patients with some persisting symptom or interest in their own medical history, whereas patients experiencing avoidance may remain undiscovered. Therefore, inclusion by advertisement may lead to underestimation, as well as overestimation, of the chance to come out well after awareness. Referral requires that the patient has told someone in the medical staff about their awareness experience, which in our study was the case in only 50% of the patients. Referral can also be based on the fact that a patient has contacted medical help because of mental illness, another source of sample bias. Closed claims analysis presumes active action from the patient, and this can also be associated with a wish for economic compensation.

Our results indicate that patients may not disclose an awareness experience spontaneously, previously reported by Osterman et al.  2It was more common to tell family members than medical personnel. Thirteen of our patients were met by skepticism when they told their awareness story.

The 46 cases in our study constitute a mix of different ages, operations, and diagnoses. Five of the patients were children. This finding demonstrates that awareness is not restricted to high-risk surgery or high-risk patients.17The year in which the episode of awareness occurred varied. The median year was 1980 (range, 1935–2001). Despite the fact that many of the awareness episodes in this study happened several years ago, the unprompted own description (table 1, number 2) clearly revealed most answers to our questions spontaneously. Many patients reported that they could remember “like it happened yesterday.” van der Kolk et al.  18,19have described that memories tend to be of different quality. Personal traumatic memories are often in some aspects permanent and do not tend to fade over the years as more ordinary memories do. This may be of importance to the quality of the interviews despite that some of the episodes happened many years ago. In accordance with our own previous findings, 17% had delayed explicit memories.9 

Because awareness often leads to dissatisfaction and concern during subsequent anesthetics, it is not surprising that 41% reported that they were uncomfortable in anticipation of their next anesthesia, the one after being aware. With time and additional personal experience of successful anesthesia, this attitude faded, and before their most recent operation, only 9% maintained similar negative feelings, indicating reversibility.

It is interesting to notice that 33 (42%) of 79 patients being interviewed falsely considered themselves to be awareness victims before the interview.


We did not make any attempt to reach the seven patients who declined to participate in the study. Avoidance is a well-known behavior in patients with stress disorders, and we do not know whether this was the case in these seven patients. However, they could have denied ever having experienced awareness in the first interview, if avoidance was their primary goal. It should also be noted that they have consented to further anesthesia. There may also be other patients with grave avoidance behavior due to awareness, who will not show up for further anesthesia even if they badly need to. Finally, long-term memory may certainly be clouded in some cases.

Selection bias may affect the incidence and severity of late psychological symptoms in retrospective studies. We interviewed consecutive patients consenting for surgery about previous awareness and found initial problems comparable to those in previous studies, but a considerably lower incidence and less pronounced severity of late psychological symptoms. The method for recruiting patients in studies on late psychological symptoms after awareness may affect the apparent severity significantly.

Myles PS, Williams DL, Hendrata M, Anderson H, Weeks AM: Patient satisfaction after anaesthesia and surgery: Results of a prospective survey of 10,811 patients. Br J Anaesth 2000; 84:6–10
Osterman JE, Hopper J, Heran WJ, Keane TM, van der Kolk BA: Awareness under anesthesia and the development of posttraumatic stress disorder. Gen Hosp Psychiatry 2001; 23:198–204
Moerman N, Bonke B, Oosting J: Awareness and recall during general anesthesia: Facts and feelings. Anesthesiology 1993; 79:454–64
Domino KB, Posner KL, Caplan RA, Cheney FW: Awareness during anesthesia: A closed claims analysis. Anesthesiology 1999; 90:1053–6
Schwender D, Kunze-Kronawitter H, Dietrich P, Klasing S, Forst H, Madler C: Conscious awareness during general anaesthesia: Patients' perceptions, emotions, cognition and reactions. Br J Anaesth 1998; 80:133–9
Hutchinson R: Awareness during surgery: A study of its incidence. Br J Anaesth 1961; 33:463–9
Sebel PS, Bowdle TA, Ghoneim MM, Rampil IJ, Padilla RE, Gan TJ, Domino KB: The incidence of awareness during anesthesia: A multicenter United States study. Anesth Analg 2004; 99:833–9
Ranta SO, Laurila R, Saario J, Ali-Melkkila T, Hynynen M: Awareness with recall during general anesthesia: Incidence and risk factors. Anesth Analg 1998; 86:1084–9
Sandin RH, Enlund G, Samuelsson P, Lennmarken C: Awareness during anaesthesia: A prospective case study. Lancet 2000; 355:707–11
Liu WH, Thorp TA, Graham SG, Aitkenhead AR: Incidence of awareness with recall during general anaesthesia. Anaesthesia 1991; 46:435–7
Nordstrom O, Engstrom 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
Ekman A, Lindholm ML, Lennmarken C, Sandin R: Reduction in the incidence of awareness using BIS monitoring. Acta Anaesthesiol Scand 2004; 48:20–6
Myles PS, Leslie K, McNeil J, Forbes A, Chan MT: Bispectral index monitoring to prevent awareness during anaesthesia: The B-Aware randomised controlled trial. Lancet 2004; 363:1757–63
Meyer B, Blacher R: A traumatic neurotic reaction induced by succinylcholine chloride. NZ Med J 1961; 61:1255–61
Lennmarken C, Bildfors K, Enlund G, Samuelsson P, Sandin R: Victims of awareness. Acta Anaesthesiol Scand 2002; 46:229–31
Brice DD, Hetherington RR, Utting JE: A simple study of awareness and dreaming during anaesthesia. Br J Anaesth 1970; 42:535–4
Davidson AJ, Huang GH, Czarnecki C, Gibson MA, Stewart SA, Jamsen K, Stargatt R: Awareness during anesthesia in children: A prospective cohort study. Anesth Analg 2005; 100:653–61
van der Kolk BA, Fisler R: Dissociation and the fragmentary nature of traumatic memories: Overview and exploratory study. J Trauma Stress 1995; 8:505–25
van Der Kolk BA, Burbridge JA, Suzuki J: The psychobiology of traumatic memory: Clinical implications of neuroimaging studies. Ann N Y Acad Sci 1997; 821:99–113