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Patients' conscious recollections from cardiac anesthesia
Patients’ Conscious Recollections From Cardiac Anesthesia Seppo O.-V. Ranta, MD, Pirkko Herranen, RN, and Markku Hynynen, MD Objective: To estimate the current incidence of conscious recollections from the time of anesthesia, the contribution of anesthetic drugs to this incidence, and the patients’ experience of cardiac anesthesia and surgery. Design: Prospective, horizontal survey of cardiac surgery patients using structured interview method. Setting: Tertiary care university hospital. Participants: All cardiac surgery patients during 1 year (n ⴝ 1,218). Interventions: None. Measurements and Main Results: Of 1,218 patients operated on, 929 were interviewed. The patients’ memories were classified to estimate the number of patients with possible or definite intraoperative awareness and later conscious recall. The use of anesthetics was estimated from anesthetic charts for patients with awareness and recall and control patients. These charts were compared using Poisson regression. The incidence of definite awareness with recall was
T
HE INCIDENCE OF awareness with recall during anesthesia has been estimated to be 0.15% to 0.7% for general surgery1-4 and 1% to 23% for cardiac surgery.5-8 It generally has been accepted that cardiac surgery carries an increased risk of awareness.9,10 In contrast to this view, Dowd et al11 reported a frequency of awareness with recall of only 0.3% in fast-track cardiac surgical patients. The authors’ group showed earlier that the risk of awareness can be reduced by giving information to cardiac anesthesiologists regarding anesthetic techniques. This information, which is included in the education files of the unit, suggests continuous use of either intravenous or inhalation anesthetic drugs and use of minimal doses of muscle relaxants. As these techniques became generally accepted in this institution, the authors assumed that the risk of awareness during cardiac surgery would be further reduced. A study was designed in which a structured interview method was used to determine the present incidence and risk factors for awareness and recall during cardiac anesthesia. The dose of anesthetic agents in patients with conscious recollections of awareness was correlated with the dose in patients without recall by Poisson regression method, which adjusts for the rare occurrence of awareness with recall. Only a few studies previously have undertaken such a correlation.3,8
From the Departments of Anaesthesia and Intensive Care Medicine, Helsinki University Central Hospital, Helsinki; and Department of Anaesthesia and Intensive Care Medicine, Helsinki University Central Hospital, Jorvi Hospital, Espoo, Finland. Supported in part by a research grant from the Finnish-Norwegian Medical Foundation and from the Finnish Medical Foundation. Presented in part at the Fourth International Symposium on Memory and Awareness in Anaesthesia, London, UK, July 11-12, 1998. Address reprint requests to Seppo O.-V. Ranta, MD, Department of Anaesthesia, Helsinki University Central Hospital, Children’s Hospital, Stenba¨ckinkatu 11, FIN-00290 Helsinki, Finland. E-mail: [email protected] Copyright 2002, Elsevier Science (USA). All rights reserved. 1053-0770/02/1604-0007$35.00/0 doi:10.1053/jcan.2002.125149 426
0.5% (5 patients), and the incidence of possible recall was 2.3% (21 patients). A lower dose of midazolam was used for the patients with awareness and recall. Only 1 patient rated the experience of awareness as the worst perioperative memory. Benzodiazepine premedication caused amnesia for the preoperative period but not for the time of anesthesia. Conclusion: The incidence of awareness and recall is similar to the incidence reported during general surgery. Cardiac surgery does not carry increased risk of awareness. Benzodiazepines given during anesthesia are effective in decreasing the incidence of recalled awareness, and the experience of awareness is not often particularly traumatizing. Premedication with benzodiazepine is not effective in preventing recollection of anesthesia, however. Copyright 2002, Elsevier Science (USA). All rights reserved. KEY WORDS: anesthesia, awareness, cardiac surgery, complications, memory METHODS The present study is a prospective, open, cross-sectional survey of the explicit memories of cardiac surgery in a tertiary care center. All cardiac surgery patients operated on during a 12-month period beginning January 13, 1995, were included in the study. After obtaining permission from the institutional ethics committee, the patients were structurally interviewed in the postoperative wards by 2 of the authors (S.V.-O.R. and P.H.) using the questions originally formulated by Brice et al12 (Table 1). Emphasis was placed on the patients’ own idea of whether they had any intraoperative recollections. This was done because a patient’s own experience and interpretation of that experience cause the possible psychological aftereffects. Patients unable to communicate in the interview because of disease or language, patients who were not willing to participate, and patients who postoperatively stayed in the intensive care unit (ICU) for ⬎5 days were excluded from the study. After the interviews, the dosing of anesthetics was recorded from the anesthetic charts in all cases of possible awareness with recall or unpleasant dreams. For control purposes, the dosing was recorded in 308 random cases selected from the group of interviewed patients without recall of awareness. Continuous administration of an anesthetic was defined as follows: Administration of an inhaled or intravenous anesthetic was started within 15 minutes after induction and continued throughout the anesthesia until the end of surgery without breaks ⬎15 minutes.3,8 The dose of the inhaled anesthetic drugs was calculated from the anesthetic charts as follows: The inspired concentration of the anesthetic agent was multiplied by the time (in minutes) that this concentration was used. These totals for different concentrations and times were added to a grand total, which was divided by the anesthesia time. This figure was
Table 1. Questions Asked During the Interviews 1. What is the last thing you remember before going to sleep for the operation? 2. What is the first thing you remember after waking after the operation? 3. Do you remember anything in between? 4. Did you have any dreams? 5. What was the most unpleasant thing you remember from your operation and anesthesia?
Journal of Cardiothoracic and Vascular Anesthesia, Vol 16, No 4 (August), 2002: pp 426-430
PATIENTS’ RECOLLECTIONS FROM CARDIAC ANESTHESIA
427
Table 2. Cardiac Surgery Procedures During the Year of Study Operated Patients Procedure
CABG surgery Valvular surgery CABG plus valvular surgery Heart transplantation Lung transplantation Heart and lung transplantation Other procedures Procedure not recorded Total
n
934 141 72 22 2 6 38 3 1,218
% of Total
76.7 11.6 5.9 1.8 0.2 0.5 3.1 0.2 100
Interviewed Patients n
% Interviewed of Operated
736 104 50 15 0 2 19 3
78.8 73.8 69.4 68.2 0 33.3 50.0 100.0
929
76.3
(mean Fi percentage). Frequency of use of the following drugs was also included in the models: diazepam, midazolam, lorazepam, isoflurane, and enflurane. For all statistical comparisons, p value ⬍ 0.05 was considered significant. RESULTS
Abbreviations: CABG, coronary artery bypass graft.
used as an estimate of how much anesthetic the anesthesiologist intended to give to the patient.3,8 For the analysis of intravenous anesthetic agents, dosing in relation to patient weight and anesthesia time was used. The anesthetic time was defined as the time from the beginning of the induction until the time the patient was transferred to the ICU. For statistical testing, chi-squared test, t-test, Mann-Whitney U test, and one-way analysis of variance with Tukey’s honestly significant differences post hoc test were used as appropriate. In addition, Poisson regression was used to create models of factors influencing the occurrence of awareness with recall. For this analysis, 25 patients with possible awareness (n ⫽ 21) or unpleasant dreams (n ⫽ 4) were used, and 308 patients randomly selected from the group of interviewed patients were used as controls. For the Poisson analysis, anesthetic data of all patients with possible awareness and patients with unpleasant dreams were used. The outcome (recall of awareness or dreams or no awareness and no dreams) formed the dependent factor. The independent factors entered into the Poisson regression analysis included patient sex; surgical procedure; cardiopulmonary bypass time; nature of dosing the anesthetic agents (continuous or noncontinuous intravenous infusion or inhaled vapor); body mass index of the patient; dosing of lorazepam premedication (mg/kg); dosing of diazepam, midazolam, lorazepam, thiopental, propofol, fentanyl, sufentanil, alfentanil, and pancuronium (g/kg/min); and dosing of isoflurane and enflurane
During the study period, 1,218 cardiac surgery patients were operated on, and 929 (76%) were interviewed. Cardiac procedures done on these patients are listed in Table 2. The interviews were done in the immediate postoperative period (median, postoperative day 4; range, postoperative days 1 to 18). The time between the operation and interview was similar in patients with recall of awareness and in patients without recall. Of patients, 289 were not interviewed for the following reasons: 149 (51.6%) could not be reached before they were transferred to other hospitals after the operation, 62 (21.5%) stayed in the ICU for ⬎5 days, 38 (13.1%) died before the interview, 25 (8.7%) developed neurologic symptoms preventing interview, 6 (2.0%) did not speak Finnish, 2 (0.7%) had psychiatric symptoms preventing interview, and 7 (2.4%) had various other reasons (eg, another operation in the immediate postoperative period) for noninterview. The patients’ last memories before induction of general anesthesia were influenced by the age of the patient and the nature of premedication: benzodiazepines or opioids (Table 3). Most patients in the opioid group received a combination of morphine and scopolamine. The ages of patients receiving benzodiazepines or opioids as premedication were not significantly different from each other. One patient (0.1% of interviewed patients) had long-lasting intraoperative recollections, and 4 patients (0.4%) recalled some intraoperative objective memories; the incidence of awareness with recall in the interviewed patients was 0.5% (Table 4). In addition, 16 patients had memories that could be of intraoperative origin, but these patients did not recollect any objective facts that could be traced back to the intraoperative period. Some of the recollections of the latter group may have originated immediately before the induction of
Table 3. Last Recollection of the Patient Before Induction of General Anesthesia in Relation to the Premedication Used or Age Premedication Last Recollection
Unknown
No Premedication
Before receiving premedications Receiving the premedication Transferring to the operating floor Entry to the operating room Induction of anesthesia No recollection
1 (14.3%) 1 (14.3%) 1 (14.3%) 0 3 (42.8%) 1 (14.3%)
0 2 (28.6%) 1 (14.3%) 1 (14.3%) 2 (28.6%) 1 (14.3%)
Totals
7 (2.1%)
7 (2.1%)
Benzodiazepine*†
Age n
95% CI Range (y)
Opioid†‡
Row Total
13 (5.7%) 49 (21.4%) 74 (32.3%) 29 (12.7%) 50 (21.8%) 14 (6.1%)
5 (5.6%) 7 (7.8%) 14 (15.6%) 22 (24.4%) 36 (41.4%) 6 (6.7%)
18 (5.6%) 58 (17.9%) 88 (27.2%) 52 (16.0%) 87 (26.9%) 21 (6.5%)
38 (4.1%) 177 (19.1%) 261 (28.1%) 158 (17.0%) 242 (26.0%) 53 (5.7%)
60.7-67.3 60.5-63.4 60.9-63.5 59.6-62.8 56.1-58.8§ 66.2-70.7
229 (68.8%)
90 (27.0%)
333 (100.0%)
929 (100.0%)
60.5-61.9
NOTE. Figures are number of patients (percentage). Data in relation to the premedication were analyzed from a randomly selected patient database (n ⫽ 333) used for the medication analysis. Data in relation to patient age were analyzed using the whole interview database (n ⫽ 929). Abbreviation: CI, confidence interval. *In the benzodiazepine group, 227 patients received lorazepam and 2 diazepam. †Patients in the opioid group lost their conscious (explicit) recollections later than patients in the benzodiazepine group (p ⬍ 0.005). ‡In the opioid group, 81 patients received combination of morphine and scopolamine, 5 patients oxycodone intramuscularly, and 4 patients morphine intravenously or intramuscularly without supplementation of scopolamine. §Age of patients recalling the induction of anesthesia is younger than age of patients losing conscious recollections earlier (p ⬍ 0.001).
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Table 4. Description of Patients With Awareness and Recall During Cardiac Surgery Patient No.
Awareness Class*
Age (y), Sex
Type of Operation
1
3
54, M
CABG
2
2
68, M
CABG
3
2
47, M
CABG
4 5
2 2
53, M 71, M
CABG CABG
6 7 8
1 1 1
72, M 70, M 54, M
CABG CABG CABG ⫹ MVR
9
1
60, M
CABG
10
1
69, M
CABG
11
1
82, M
CABG
12
1
61, M
CABG
13
1
53, M
CABG
14 15 16 17 18 19
1 1 1 1 1 1
52, 53, 82, 55, 68, 57,
M F M M M M
CABG CABG CABG CABG CABG CABG
20
1
50, M
CABG
21
1
74, F
CABG
Notes of the Operation and Recollections of the Patient
Suffered from serious mental depression before the operation, and antidepressive medication was started a week before the operation. Recollects waking with much pain in his chest “like the chest was opened with a saw.” Saw people moving around him and heard women laughing. Also felt pain in his neck. Thinks that he was aware of what is going on around him for 2 to 3 h This patient underwent an unsuccessful coronary angioplasty and was immediately transferred to the OR for surgical CABG. The patient recollects discussions, pain in his neck, and a tracheal tube in his throat The patient underwent a second operation because of postoperative bleeding 6 h after the primary operation. The patient recollects being unable to open his eyes, shortness of breath, and utmost anxiety. Then remembers falling asleep again Recollects the intubation Recollects hearing a rattling noise, which the patient attributes to sawing of the sternum. Recollects thinking that one should not hear this Pain that the patient attributes to the time of awakening Heard male voices; the patient attributes this to the preoperative period in the OR Memories of movement. The patient cannot attribute the recollection to a specified time Remembers a discussion about reoperation. The patient underwent a reoperation because of inadequate hemostasis 6.5 hours after the primary operation. Recollections are likely to have occurred during the interval between the operations Opened his eyes during the operation. Does not remember this. Recollects loud male and female voices, “like in a noisy restaurant.” The patient attributes this to the postoperative period in the ICU Unpleasant feeling coupled with nausea. The patient attributes this to the intraoperative period Recollects that tubes were pulled out of his chest. This was accompanied with slight pain. The patient attributes this to the last phase of the operation. AEP monitoring was used during this operation but not after the cardiopulmonary bypass period. The memories may originate in the ICU period Remembers someone talking to him. An unpleasant feeling in his throat. Cannot attribute the recollections to a specified time. Recollects being transported from one place to another Recollects having seen some lights Remembers feeling very bad, considered himself as dead Recollects few people talking to him about fixing the intubation tube Recollects seeing tubes and drains Recollects falling asleep. Then felt pain in the chest and simultaneously heard somebody saying “we are removing something and you may feel pain.” The patient attributes this to the preoperative period. That the patient was told that “you may feel pain,” suggests that the recollections are not intraoperative The patient underwent a second operation because of postoperative bleeding 4 hours after the primary operation. Recollects hearing a discussion with a concerned tone. During that time thought that he is still in the middle of an operation Recollects dreaming about somebody slaughtering sheep in an attic. Simultaneously felt something in her throat. The feeling was frightening
Abbreviations: CABG, coronary artery bypass graft; MVR, mitral valve replacement; OR, operating room; ICU, intensive care unit; AEP, auditory evoked potential. *Classification of awareness: 1 ⫽ unclear memories that could be of intraoperative origin; 2 ⫽ clear momentary intraoperative memories; 3 ⫽ clear, long-lasting intraoperative memories.
anesthesia or during the transfer to or stay in the ICU. The incidence of possible awareness is 2.3% when all these cases are included. There was no difference in the gender or age distribution of the patients with awareness with recall and patients without recall.
The doses of anesthetic agents are shown in Table 5. There was a significant difference in the dose of midazolam between the patients with awareness and recall and patients without recall in the Poisson regression model. Lorazepam premedication (the most frequently used benzodiazepine premedication)
PATIENTS’ RECOLLECTIONS FROM CARDIAC ANESTHESIA
429
Table 5. Dose of Anesthetic Drugs During Cardiac Surgery Given to Patients With and Without Awareness and Recall Dose
Anesthetic
n
Median
Range
n
Median
Range
p (Poisson regression model)
Diazepam (g/kg/min) Lorazepam (g/kg/min) Midazolam (g/kg/min) Propofol (g/kg/min) Thiopental (g/kg/min) Alfentanil (g/kg/min) Fentanyl (g/kg/min) Sufentanil (g/kg/min) Pancuronium (g/kg/min) Enflurane (FiAA%/min)* Isoflurane (FiAA%/min)*
11 2 10 2 2 1 13 7 20 7 13
0.47 0.14 0.88 26.5 11.4
0.24-0.96 0.10-0.18 0.46-1.94 4.5-48.6 4.8-18.0 1.01 0.11-0.32 0.02-0.05 0.35-0.82 0.09-0.63 0.14-0.60
113 33 157 24 65 35 189 79 297 91 205
0.60 0.17 1.14 4.4 9.7 1.45 0.22 0.04 0.56 0.37 0.33
0.11-2.01 0.08-0.53 0.29-3.18 0.4-88.2 2.4-49.7 0.29-3.99 0.02-6.45 0.01-0.18 0.06-1.00 0.04-0.87 0.02-0.95
0.149 0.491 0.047 0.653 0.713 0.319 0.841 0.711 0.277 0.106 0.789
Patients With Awareness
0.22 0.04 0.52 0.12 0.34
Patients Without Awareness
Relative Risk for 1 Unit Change in Dose
NA NA 0.13 NA NA NA NA NA NA NA NA
Abbreviations: NA, not assessed; Fi, inspiratory fraction. *The inspiratory concentration that would have been delivered had the total dose of the inhalation anesthetic been divided equally during the whole duration of anesthesia. For details, see Methods section.
had no significant influence on the incidence of recall of awareness in the Poisson regression model. One of the 21 patients (patient 3, Table 4) with definite or possible intraoperative awareness and recall named that experience as the worst of what they had gone through during the cardiac operation. The worst perioperative experience of the patients is shown in Table 6. DISCUSSION
The authors surveyed the experience of 929 cardiac surgery patients. The incidence of awareness with postoperative recall in the patients undergoing cardiac surgery was 0.5% when only the patients with objective recollections were included. This figure is smaller than in many previous reports in cardiac surgical patients,5-7 including the authors’ previous report,8 but of similar magnitude as in another study by Dowd et al11 undertaken in fast-track cardiac surgery patients. The 0.5% incidence of objective recollections is close to that reported in studies of noncardiac surgery populations.2,3,13 It seems that modern cardiac anesthesia does not carry any special increased risk of conscious recollection of awareness. When all possible cases of awareness with recall in the current study are included, the incidence was 2.3%, which is a
Table 6. Recollections From the Perioperative Period of Cardiac Surgery That the Patients Regarded as the Worst Experience Experience
n (% of Total Respondents)
Nothing Postoperative pain Being intubated on the respirator PONV* Thirst Drains or their removal Preoperative anxiety/fear Removal of the tracheal tube Various other experiences Unknown
437 (47.0%) 99 (10.7%) 54 (5.8%) 53 (5.7%) 47 (5.1%) 33 (3.5%) 27 (2.9%) 21 (2.3%) 155 (16.7%) 3 (0.3%)
*Postoperative nausea and vomiting.
higher incidence than that found (0.7%) in another study during noncardiac surgery.3 One explanation for the higher incidence during cardiac surgery may be the more frequent use of benzodiazepines as the principal anesthetic in cardiac anesthesia compared with the volatile anesthetic agents used during noncardiac surgery. Benzodiazepines are excellent drugs in producing amnesia but are not reliable in producing unconsciousness during general anesthesia.14 Also, the amnesia produced by benzodiazepines is not as profound for emotionally significant stimuli as for nonsignificant stimuli, which may explain recall of highly emotional stimuli during a surgical operation.15 The recovery period in the ICU is probably also likely to cause memories that may be interpreted as originating from the period of anesthesia. In studies evaluating explicit awareness during anesthesia, figures of possible awareness are reported only infrequently3 even though the exact reconstruction and timing of the events memorized are not always possible. All studies of intraoperative recall have to rely on the patient’s memories,9,16 which sometimes may be quite confusing. Contrary to many other articles, the authors have chosen to report all cases, including suspect patients. Only 1 of the 21 patients with definite or possible awareness with postoperative recall considered this recollection as the worst experience during the cardiac surgery procedure. Probably the relatively high doses of opioids prevented painful awareness. Also, based on earlier findings during general surgery, it seems that intraoperative awareness with postoperative recall is relatively rarely a traumatizing experience.3 Lower doses of midazolam were used in patients with awareness and recall, and a lower median dose of midazolam seemed to be an independent risk factor for postoperative recall. Possibly the profound amnestic properties of midazolam, in doses large enough, play a significant role in preventing recall of conscious awareness.15,17 The present finding is in agreement with the authors’ previous observations that patients with awareness and recall receive smaller doses of principal anesthetic agents than patients without awareness and recall.3 Comparisons of doses of anesthetic drugs have been undertaken
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previously only in few studies.3 The lack of difference in the dosing of drugs other than midazolam may be due in part to the low power of the statistical methods in detecting subtle differences because the number of patients in each category of drug combinations was relatively small. Variation in the individual amnestic response to anesthetics makes it difficult to find differences in such an infrequent event as conscious awareness with recall. The anesthesia technique was not standardized for the present study, which was undertaken to find risk factors of conscious awareness during normal clinical situations. During this cross-sectional evaluation of all anesthetics administered during a 12-month period, various anesthetic drugs and their combinations were used. It seems also that benzodiazepine premedication produces a higher degree of amnesia for the preoperative period compared with opioids even if supplemented with scopolamine. Benzodiazepine premedication seems not to be effective, however, in preventing conscious memories from the time of anesthesia. Similar amnestic effect for the preoperative period is produced by old age itself. The minor role of benzodiazepine premedication in preventing intraoperative awareness and recall is also suggested by another study.4
This study excluded patients staying in the ICU longer than normal. Most of these patients had a complicated course of disease or surgery, had sedative medications not used for patients without complications, and often underwent secondary procedures. In such patients, it is difficult to interpret the phase of the operation or postoperative care from which the recollections originate. More studies and better tools for timing and quantifying patient recollections are needed. In conclusion, these results suggest that the risk of awareness with recall during cardiac surgery is similar to that reported during other types of procedures requiring general anesthesia. When administered in combination with other anesthetic agents, higher doses of midazolam given during anesthesia seem to be efficient in decreasing the recall of conscious awareness in cardiac surgical patients. Benzodiazepines given as premedication cause amnesia for the preoperative, but not intraoperative, period. The experience of awareness with postoperative recall is not always emotionally traumatizing. ACKNOWLEDGMENT The authors express their gratitude to biostatistician Mr. Arttu Laine, for performing the Poisson analysis.
REFERENCES 1. Jones JG: Perception and memory during general anaesthesia. Br J Anaesth 73:31-37, 1994 2. Liu WH, Thorp TA, Graham SG, Aitkenhead AR: Incidence of awareness with recall during general anaesthesia. Anaesthesia 46:435437, 1991 3. Ranta SOV, Laurila R, Saario J, et al: Awareness with recall during general anesthesia: Incidence and risk factors. Anesth Analg 86:1084-1089, 1998 4. Sandin RH, Enlund G, Samuelsson P, Lennmarken C: Awareness during anaesthesia: A prospective case study. Lancet 355:707-711, 2000 5. Kim CL: Awareness during cardiopulmonary bypass. J Am Assoc Nurs Anesth 46:373-383, 1978 6. Goldmann L, Shah MV, Hebden MW: Memory of cardiac anaesthesia: Psychological sequelae in cardiac patients of intraoperative suggestion and operating room conversation. Anaesthesia 42:596-603, 1987 7. Phillips AA, McLean RF, Devitt JH, Harrington EM: Recall of intraoperative events after general anaesthesia and cardiopulmonary bypass. Can J Anaesth 40:922-926, 1993 8. Ranta S, Jussila J, Hynynen M: Recall of awareness during cardiac anaesthesia: Influence of feedback information to the anaesthesiologist. Acta Anaesthesiol Scand 40:554-560, 1996 9. Ghoneim MM, Block RI: Learning and consciousness during general anesthesia. Anesthesiology 76:279-305, 1992
10. Tempe DK, Siddique RA: Awareness during cardiac surgery. J Cardiothorac Vasc Anesth 13:214-219, 1999 11. Dowd NP, Cheng DC, Karski JM, et al: Intraoperative awareness in fast-track cardiac anesthesia. Anesthesiology 89:1068-1073, 1998 12. Brice DD, Hetherington RR, Utting JE: A simple study of awareness and dreaming during anaesthesia. Br J Anaesth 42:535-542, 1970 13. Nordstro¨ m O, Engstro¨ m S, Persson S, Sandin R: Incidence of awareness in total IV anaesthesia based on propofol, alfentanil and neuromuscular blockade. Acta Anaesthesiol Scand 41:978-984, 1997 14. Russell IF: Midazolam-alfentanil: An anaesthetic? An investigation using the isolated forearm technique. Br J Anaesth 70:42-46, 1993 15. Ghoneim MM, Mewaldt SP: Benzodiazepines and human memory: A review. Anesthesiology 72:926-938, 1990 16. Kihlstrom JF, Schacter DL: Anaesthesia, amnesia, and the cognitive unconscious, in Bonke B, Fitch W, Millar K (ed): Memory and Awareness in Anaesthesia. Amsterdam, Swets & Zeitlinger Publishers, 1990, pp 21-44 17. Miller DR, Blew PG, Martineau RJ, Hull KA: Midazolam and awareness with recall during total intravenous anaesthesia. Can J Anaesth 43:946-953, 1996
T
HE INCIDENCE OF awareness with recall during anesthesia has been estimated to be 0.15% to 0.7% for general surgery1-4 and 1% to 23% for cardiac surgery.5-8 It generally has been accepted that cardiac surgery carries an increased risk of awareness.9,10 In contrast to this view, Dowd et al11 reported a frequency of awareness with recall of only 0.3% in fast-track cardiac surgical patients. The authors’ group showed earlier that the risk of awareness can be reduced by giving information to cardiac anesthesiologists regarding anesthetic techniques. This information, which is included in the education files of the unit, suggests continuous use of either intravenous or inhalation anesthetic drugs and use of minimal doses of muscle relaxants. As these techniques became generally accepted in this institution, the authors assumed that the risk of awareness during cardiac surgery would be further reduced. A study was designed in which a structured interview method was used to determine the present incidence and risk factors for awareness and recall during cardiac anesthesia. The dose of anesthetic agents in patients with conscious recollections of awareness was correlated with the dose in patients without recall by Poisson regression method, which adjusts for the rare occurrence of awareness with recall. Only a few studies previously have undertaken such a correlation.3,8
From the Departments of Anaesthesia and Intensive Care Medicine, Helsinki University Central Hospital, Helsinki; and Department of Anaesthesia and Intensive Care Medicine, Helsinki University Central Hospital, Jorvi Hospital, Espoo, Finland. Supported in part by a research grant from the Finnish-Norwegian Medical Foundation and from the Finnish Medical Foundation. Presented in part at the Fourth International Symposium on Memory and Awareness in Anaesthesia, London, UK, July 11-12, 1998. Address reprint requests to Seppo O.-V. Ranta, MD, Department of Anaesthesia, Helsinki University Central Hospital, Children’s Hospital, Stenba¨ckinkatu 11, FIN-00290 Helsinki, Finland. E-mail: [email protected] Copyright 2002, Elsevier Science (USA). All rights reserved. 1053-0770/02/1604-0007$35.00/0 doi:10.1053/jcan.2002.125149 426
0.5% (5 patients), and the incidence of possible recall was 2.3% (21 patients). A lower dose of midazolam was used for the patients with awareness and recall. Only 1 patient rated the experience of awareness as the worst perioperative memory. Benzodiazepine premedication caused amnesia for the preoperative period but not for the time of anesthesia. Conclusion: The incidence of awareness and recall is similar to the incidence reported during general surgery. Cardiac surgery does not carry increased risk of awareness. Benzodiazepines given during anesthesia are effective in decreasing the incidence of recalled awareness, and the experience of awareness is not often particularly traumatizing. Premedication with benzodiazepine is not effective in preventing recollection of anesthesia, however. Copyright 2002, Elsevier Science (USA). All rights reserved. KEY WORDS: anesthesia, awareness, cardiac surgery, complications, memory METHODS The present study is a prospective, open, cross-sectional survey of the explicit memories of cardiac surgery in a tertiary care center. All cardiac surgery patients operated on during a 12-month period beginning January 13, 1995, were included in the study. After obtaining permission from the institutional ethics committee, the patients were structurally interviewed in the postoperative wards by 2 of the authors (S.V.-O.R. and P.H.) using the questions originally formulated by Brice et al12 (Table 1). Emphasis was placed on the patients’ own idea of whether they had any intraoperative recollections. This was done because a patient’s own experience and interpretation of that experience cause the possible psychological aftereffects. Patients unable to communicate in the interview because of disease or language, patients who were not willing to participate, and patients who postoperatively stayed in the intensive care unit (ICU) for ⬎5 days were excluded from the study. After the interviews, the dosing of anesthetics was recorded from the anesthetic charts in all cases of possible awareness with recall or unpleasant dreams. For control purposes, the dosing was recorded in 308 random cases selected from the group of interviewed patients without recall of awareness. Continuous administration of an anesthetic was defined as follows: Administration of an inhaled or intravenous anesthetic was started within 15 minutes after induction and continued throughout the anesthesia until the end of surgery without breaks ⬎15 minutes.3,8 The dose of the inhaled anesthetic drugs was calculated from the anesthetic charts as follows: The inspired concentration of the anesthetic agent was multiplied by the time (in minutes) that this concentration was used. These totals for different concentrations and times were added to a grand total, which was divided by the anesthesia time. This figure was
Table 1. Questions Asked During the Interviews 1. What is the last thing you remember before going to sleep for the operation? 2. What is the first thing you remember after waking after the operation? 3. Do you remember anything in between? 4. Did you have any dreams? 5. What was the most unpleasant thing you remember from your operation and anesthesia?
Journal of Cardiothoracic and Vascular Anesthesia, Vol 16, No 4 (August), 2002: pp 426-430
PATIENTS’ RECOLLECTIONS FROM CARDIAC ANESTHESIA
427
Table 2. Cardiac Surgery Procedures During the Year of Study Operated Patients Procedure
CABG surgery Valvular surgery CABG plus valvular surgery Heart transplantation Lung transplantation Heart and lung transplantation Other procedures Procedure not recorded Total
n
934 141 72 22 2 6 38 3 1,218
% of Total
76.7 11.6 5.9 1.8 0.2 0.5 3.1 0.2 100
Interviewed Patients n
% Interviewed of Operated
736 104 50 15 0 2 19 3
78.8 73.8 69.4 68.2 0 33.3 50.0 100.0
929
76.3
(mean Fi percentage). Frequency of use of the following drugs was also included in the models: diazepam, midazolam, lorazepam, isoflurane, and enflurane. For all statistical comparisons, p value ⬍ 0.05 was considered significant. RESULTS
Abbreviations: CABG, coronary artery bypass graft.
used as an estimate of how much anesthetic the anesthesiologist intended to give to the patient.3,8 For the analysis of intravenous anesthetic agents, dosing in relation to patient weight and anesthesia time was used. The anesthetic time was defined as the time from the beginning of the induction until the time the patient was transferred to the ICU. For statistical testing, chi-squared test, t-test, Mann-Whitney U test, and one-way analysis of variance with Tukey’s honestly significant differences post hoc test were used as appropriate. In addition, Poisson regression was used to create models of factors influencing the occurrence of awareness with recall. For this analysis, 25 patients with possible awareness (n ⫽ 21) or unpleasant dreams (n ⫽ 4) were used, and 308 patients randomly selected from the group of interviewed patients were used as controls. For the Poisson analysis, anesthetic data of all patients with possible awareness and patients with unpleasant dreams were used. The outcome (recall of awareness or dreams or no awareness and no dreams) formed the dependent factor. The independent factors entered into the Poisson regression analysis included patient sex; surgical procedure; cardiopulmonary bypass time; nature of dosing the anesthetic agents (continuous or noncontinuous intravenous infusion or inhaled vapor); body mass index of the patient; dosing of lorazepam premedication (mg/kg); dosing of diazepam, midazolam, lorazepam, thiopental, propofol, fentanyl, sufentanil, alfentanil, and pancuronium (g/kg/min); and dosing of isoflurane and enflurane
During the study period, 1,218 cardiac surgery patients were operated on, and 929 (76%) were interviewed. Cardiac procedures done on these patients are listed in Table 2. The interviews were done in the immediate postoperative period (median, postoperative day 4; range, postoperative days 1 to 18). The time between the operation and interview was similar in patients with recall of awareness and in patients without recall. Of patients, 289 were not interviewed for the following reasons: 149 (51.6%) could not be reached before they were transferred to other hospitals after the operation, 62 (21.5%) stayed in the ICU for ⬎5 days, 38 (13.1%) died before the interview, 25 (8.7%) developed neurologic symptoms preventing interview, 6 (2.0%) did not speak Finnish, 2 (0.7%) had psychiatric symptoms preventing interview, and 7 (2.4%) had various other reasons (eg, another operation in the immediate postoperative period) for noninterview. The patients’ last memories before induction of general anesthesia were influenced by the age of the patient and the nature of premedication: benzodiazepines or opioids (Table 3). Most patients in the opioid group received a combination of morphine and scopolamine. The ages of patients receiving benzodiazepines or opioids as premedication were not significantly different from each other. One patient (0.1% of interviewed patients) had long-lasting intraoperative recollections, and 4 patients (0.4%) recalled some intraoperative objective memories; the incidence of awareness with recall in the interviewed patients was 0.5% (Table 4). In addition, 16 patients had memories that could be of intraoperative origin, but these patients did not recollect any objective facts that could be traced back to the intraoperative period. Some of the recollections of the latter group may have originated immediately before the induction of
Table 3. Last Recollection of the Patient Before Induction of General Anesthesia in Relation to the Premedication Used or Age Premedication Last Recollection
Unknown
No Premedication
Before receiving premedications Receiving the premedication Transferring to the operating floor Entry to the operating room Induction of anesthesia No recollection
1 (14.3%) 1 (14.3%) 1 (14.3%) 0 3 (42.8%) 1 (14.3%)
0 2 (28.6%) 1 (14.3%) 1 (14.3%) 2 (28.6%) 1 (14.3%)
Totals
7 (2.1%)
7 (2.1%)
Benzodiazepine*†
Age n
95% CI Range (y)
Opioid†‡
Row Total
13 (5.7%) 49 (21.4%) 74 (32.3%) 29 (12.7%) 50 (21.8%) 14 (6.1%)
5 (5.6%) 7 (7.8%) 14 (15.6%) 22 (24.4%) 36 (41.4%) 6 (6.7%)
18 (5.6%) 58 (17.9%) 88 (27.2%) 52 (16.0%) 87 (26.9%) 21 (6.5%)
38 (4.1%) 177 (19.1%) 261 (28.1%) 158 (17.0%) 242 (26.0%) 53 (5.7%)
60.7-67.3 60.5-63.4 60.9-63.5 59.6-62.8 56.1-58.8§ 66.2-70.7
229 (68.8%)
90 (27.0%)
333 (100.0%)
929 (100.0%)
60.5-61.9
NOTE. Figures are number of patients (percentage). Data in relation to the premedication were analyzed from a randomly selected patient database (n ⫽ 333) used for the medication analysis. Data in relation to patient age were analyzed using the whole interview database (n ⫽ 929). Abbreviation: CI, confidence interval. *In the benzodiazepine group, 227 patients received lorazepam and 2 diazepam. †Patients in the opioid group lost their conscious (explicit) recollections later than patients in the benzodiazepine group (p ⬍ 0.005). ‡In the opioid group, 81 patients received combination of morphine and scopolamine, 5 patients oxycodone intramuscularly, and 4 patients morphine intravenously or intramuscularly without supplementation of scopolamine. §Age of patients recalling the induction of anesthesia is younger than age of patients losing conscious recollections earlier (p ⬍ 0.001).
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Table 4. Description of Patients With Awareness and Recall During Cardiac Surgery Patient No.
Awareness Class*
Age (y), Sex
Type of Operation
1
3
54, M
CABG
2
2
68, M
CABG
3
2
47, M
CABG
4 5
2 2
53, M 71, M
CABG CABG
6 7 8
1 1 1
72, M 70, M 54, M
CABG CABG CABG ⫹ MVR
9
1
60, M
CABG
10
1
69, M
CABG
11
1
82, M
CABG
12
1
61, M
CABG
13
1
53, M
CABG
14 15 16 17 18 19
1 1 1 1 1 1
52, 53, 82, 55, 68, 57,
M F M M M M
CABG CABG CABG CABG CABG CABG
20
1
50, M
CABG
21
1
74, F
CABG
Notes of the Operation and Recollections of the Patient
Suffered from serious mental depression before the operation, and antidepressive medication was started a week before the operation. Recollects waking with much pain in his chest “like the chest was opened with a saw.” Saw people moving around him and heard women laughing. Also felt pain in his neck. Thinks that he was aware of what is going on around him for 2 to 3 h This patient underwent an unsuccessful coronary angioplasty and was immediately transferred to the OR for surgical CABG. The patient recollects discussions, pain in his neck, and a tracheal tube in his throat The patient underwent a second operation because of postoperative bleeding 6 h after the primary operation. The patient recollects being unable to open his eyes, shortness of breath, and utmost anxiety. Then remembers falling asleep again Recollects the intubation Recollects hearing a rattling noise, which the patient attributes to sawing of the sternum. Recollects thinking that one should not hear this Pain that the patient attributes to the time of awakening Heard male voices; the patient attributes this to the preoperative period in the OR Memories of movement. The patient cannot attribute the recollection to a specified time Remembers a discussion about reoperation. The patient underwent a reoperation because of inadequate hemostasis 6.5 hours after the primary operation. Recollections are likely to have occurred during the interval between the operations Opened his eyes during the operation. Does not remember this. Recollects loud male and female voices, “like in a noisy restaurant.” The patient attributes this to the postoperative period in the ICU Unpleasant feeling coupled with nausea. The patient attributes this to the intraoperative period Recollects that tubes were pulled out of his chest. This was accompanied with slight pain. The patient attributes this to the last phase of the operation. AEP monitoring was used during this operation but not after the cardiopulmonary bypass period. The memories may originate in the ICU period Remembers someone talking to him. An unpleasant feeling in his throat. Cannot attribute the recollections to a specified time. Recollects being transported from one place to another Recollects having seen some lights Remembers feeling very bad, considered himself as dead Recollects few people talking to him about fixing the intubation tube Recollects seeing tubes and drains Recollects falling asleep. Then felt pain in the chest and simultaneously heard somebody saying “we are removing something and you may feel pain.” The patient attributes this to the preoperative period. That the patient was told that “you may feel pain,” suggests that the recollections are not intraoperative The patient underwent a second operation because of postoperative bleeding 4 hours after the primary operation. Recollects hearing a discussion with a concerned tone. During that time thought that he is still in the middle of an operation Recollects dreaming about somebody slaughtering sheep in an attic. Simultaneously felt something in her throat. The feeling was frightening
Abbreviations: CABG, coronary artery bypass graft; MVR, mitral valve replacement; OR, operating room; ICU, intensive care unit; AEP, auditory evoked potential. *Classification of awareness: 1 ⫽ unclear memories that could be of intraoperative origin; 2 ⫽ clear momentary intraoperative memories; 3 ⫽ clear, long-lasting intraoperative memories.
anesthesia or during the transfer to or stay in the ICU. The incidence of possible awareness is 2.3% when all these cases are included. There was no difference in the gender or age distribution of the patients with awareness with recall and patients without recall.
The doses of anesthetic agents are shown in Table 5. There was a significant difference in the dose of midazolam between the patients with awareness and recall and patients without recall in the Poisson regression model. Lorazepam premedication (the most frequently used benzodiazepine premedication)
PATIENTS’ RECOLLECTIONS FROM CARDIAC ANESTHESIA
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Table 5. Dose of Anesthetic Drugs During Cardiac Surgery Given to Patients With and Without Awareness and Recall Dose
Anesthetic
n
Median
Range
n
Median
Range
p (Poisson regression model)
Diazepam (g/kg/min) Lorazepam (g/kg/min) Midazolam (g/kg/min) Propofol (g/kg/min) Thiopental (g/kg/min) Alfentanil (g/kg/min) Fentanyl (g/kg/min) Sufentanil (g/kg/min) Pancuronium (g/kg/min) Enflurane (FiAA%/min)* Isoflurane (FiAA%/min)*
11 2 10 2 2 1 13 7 20 7 13
0.47 0.14 0.88 26.5 11.4
0.24-0.96 0.10-0.18 0.46-1.94 4.5-48.6 4.8-18.0 1.01 0.11-0.32 0.02-0.05 0.35-0.82 0.09-0.63 0.14-0.60
113 33 157 24 65 35 189 79 297 91 205
0.60 0.17 1.14 4.4 9.7 1.45 0.22 0.04 0.56 0.37 0.33
0.11-2.01 0.08-0.53 0.29-3.18 0.4-88.2 2.4-49.7 0.29-3.99 0.02-6.45 0.01-0.18 0.06-1.00 0.04-0.87 0.02-0.95
0.149 0.491 0.047 0.653 0.713 0.319 0.841 0.711 0.277 0.106 0.789
Patients With Awareness
0.22 0.04 0.52 0.12 0.34
Patients Without Awareness
Relative Risk for 1 Unit Change in Dose
NA NA 0.13 NA NA NA NA NA NA NA NA
Abbreviations: NA, not assessed; Fi, inspiratory fraction. *The inspiratory concentration that would have been delivered had the total dose of the inhalation anesthetic been divided equally during the whole duration of anesthesia. For details, see Methods section.
had no significant influence on the incidence of recall of awareness in the Poisson regression model. One of the 21 patients (patient 3, Table 4) with definite or possible intraoperative awareness and recall named that experience as the worst of what they had gone through during the cardiac operation. The worst perioperative experience of the patients is shown in Table 6. DISCUSSION
The authors surveyed the experience of 929 cardiac surgery patients. The incidence of awareness with postoperative recall in the patients undergoing cardiac surgery was 0.5% when only the patients with objective recollections were included. This figure is smaller than in many previous reports in cardiac surgical patients,5-7 including the authors’ previous report,8 but of similar magnitude as in another study by Dowd et al11 undertaken in fast-track cardiac surgery patients. The 0.5% incidence of objective recollections is close to that reported in studies of noncardiac surgery populations.2,3,13 It seems that modern cardiac anesthesia does not carry any special increased risk of conscious recollection of awareness. When all possible cases of awareness with recall in the current study are included, the incidence was 2.3%, which is a
Table 6. Recollections From the Perioperative Period of Cardiac Surgery That the Patients Regarded as the Worst Experience Experience
n (% of Total Respondents)
Nothing Postoperative pain Being intubated on the respirator PONV* Thirst Drains or their removal Preoperative anxiety/fear Removal of the tracheal tube Various other experiences Unknown
437 (47.0%) 99 (10.7%) 54 (5.8%) 53 (5.7%) 47 (5.1%) 33 (3.5%) 27 (2.9%) 21 (2.3%) 155 (16.7%) 3 (0.3%)
*Postoperative nausea and vomiting.
higher incidence than that found (0.7%) in another study during noncardiac surgery.3 One explanation for the higher incidence during cardiac surgery may be the more frequent use of benzodiazepines as the principal anesthetic in cardiac anesthesia compared with the volatile anesthetic agents used during noncardiac surgery. Benzodiazepines are excellent drugs in producing amnesia but are not reliable in producing unconsciousness during general anesthesia.14 Also, the amnesia produced by benzodiazepines is not as profound for emotionally significant stimuli as for nonsignificant stimuli, which may explain recall of highly emotional stimuli during a surgical operation.15 The recovery period in the ICU is probably also likely to cause memories that may be interpreted as originating from the period of anesthesia. In studies evaluating explicit awareness during anesthesia, figures of possible awareness are reported only infrequently3 even though the exact reconstruction and timing of the events memorized are not always possible. All studies of intraoperative recall have to rely on the patient’s memories,9,16 which sometimes may be quite confusing. Contrary to many other articles, the authors have chosen to report all cases, including suspect patients. Only 1 of the 21 patients with definite or possible awareness with postoperative recall considered this recollection as the worst experience during the cardiac surgery procedure. Probably the relatively high doses of opioids prevented painful awareness. Also, based on earlier findings during general surgery, it seems that intraoperative awareness with postoperative recall is relatively rarely a traumatizing experience.3 Lower doses of midazolam were used in patients with awareness and recall, and a lower median dose of midazolam seemed to be an independent risk factor for postoperative recall. Possibly the profound amnestic properties of midazolam, in doses large enough, play a significant role in preventing recall of conscious awareness.15,17 The present finding is in agreement with the authors’ previous observations that patients with awareness and recall receive smaller doses of principal anesthetic agents than patients without awareness and recall.3 Comparisons of doses of anesthetic drugs have been undertaken
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previously only in few studies.3 The lack of difference in the dosing of drugs other than midazolam may be due in part to the low power of the statistical methods in detecting subtle differences because the number of patients in each category of drug combinations was relatively small. Variation in the individual amnestic response to anesthetics makes it difficult to find differences in such an infrequent event as conscious awareness with recall. The anesthesia technique was not standardized for the present study, which was undertaken to find risk factors of conscious awareness during normal clinical situations. During this cross-sectional evaluation of all anesthetics administered during a 12-month period, various anesthetic drugs and their combinations were used. It seems also that benzodiazepine premedication produces a higher degree of amnesia for the preoperative period compared with opioids even if supplemented with scopolamine. Benzodiazepine premedication seems not to be effective, however, in preventing conscious memories from the time of anesthesia. Similar amnestic effect for the preoperative period is produced by old age itself. The minor role of benzodiazepine premedication in preventing intraoperative awareness and recall is also suggested by another study.4
This study excluded patients staying in the ICU longer than normal. Most of these patients had a complicated course of disease or surgery, had sedative medications not used for patients without complications, and often underwent secondary procedures. In such patients, it is difficult to interpret the phase of the operation or postoperative care from which the recollections originate. More studies and better tools for timing and quantifying patient recollections are needed. In conclusion, these results suggest that the risk of awareness with recall during cardiac surgery is similar to that reported during other types of procedures requiring general anesthesia. When administered in combination with other anesthetic agents, higher doses of midazolam given during anesthesia seem to be efficient in decreasing the recall of conscious awareness in cardiac surgical patients. Benzodiazepines given as premedication cause amnesia for the preoperative, but not intraoperative, period. The experience of awareness with postoperative recall is not always emotionally traumatizing. ACKNOWLEDGMENT The authors express their gratitude to biostatistician Mr. Arttu Laine, for performing the Poisson analysis.
REFERENCES 1. Jones JG: Perception and memory during general anaesthesia. Br J Anaesth 73:31-37, 1994 2. Liu WH, Thorp TA, Graham SG, Aitkenhead AR: Incidence of awareness with recall during general anaesthesia. Anaesthesia 46:435437, 1991 3. Ranta SOV, Laurila R, Saario J, et al: Awareness with recall during general anesthesia: Incidence and risk factors. Anesth Analg 86:1084-1089, 1998 4. Sandin RH, Enlund G, Samuelsson P, Lennmarken C: Awareness during anaesthesia: A prospective case study. Lancet 355:707-711, 2000 5. Kim CL: Awareness during cardiopulmonary bypass. J Am Assoc Nurs Anesth 46:373-383, 1978 6. Goldmann L, Shah MV, Hebden MW: Memory of cardiac anaesthesia: Psychological sequelae in cardiac patients of intraoperative suggestion and operating room conversation. Anaesthesia 42:596-603, 1987 7. Phillips AA, McLean RF, Devitt JH, Harrington EM: Recall of intraoperative events after general anaesthesia and cardiopulmonary bypass. Can J Anaesth 40:922-926, 1993 8. Ranta S, Jussila J, Hynynen M: Recall of awareness during cardiac anaesthesia: Influence of feedback information to the anaesthesiologist. Acta Anaesthesiol Scand 40:554-560, 1996 9. Ghoneim MM, Block RI: Learning and consciousness during general anesthesia. Anesthesiology 76:279-305, 1992
10. Tempe DK, Siddique RA: Awareness during cardiac surgery. J Cardiothorac Vasc Anesth 13:214-219, 1999 11. Dowd NP, Cheng DC, Karski JM, et al: Intraoperative awareness in fast-track cardiac anesthesia. Anesthesiology 89:1068-1073, 1998 12. Brice DD, Hetherington RR, Utting JE: A simple study of awareness and dreaming during anaesthesia. Br J Anaesth 42:535-542, 1970 13. Nordstro¨ m O, Engstro¨ m S, Persson S, Sandin R: Incidence of awareness in total IV anaesthesia based on propofol, alfentanil and neuromuscular blockade. Acta Anaesthesiol Scand 41:978-984, 1997 14. Russell IF: Midazolam-alfentanil: An anaesthetic? An investigation using the isolated forearm technique. Br J Anaesth 70:42-46, 1993 15. Ghoneim MM, Mewaldt SP: Benzodiazepines and human memory: A review. Anesthesiology 72:926-938, 1990 16. Kihlstrom JF, Schacter DL: Anaesthesia, amnesia, and the cognitive unconscious, in Bonke B, Fitch W, Millar K (ed): Memory and Awareness in Anaesthesia. Amsterdam, Swets & Zeitlinger Publishers, 1990, pp 21-44 17. Miller DR, Blew PG, Martineau RJ, Hull KA: Midazolam and awareness with recall during total intravenous anaesthesia. Can J Anaesth 43:946-953, 1996