European Review for Medical and Pharmacological Sciences 2011; 15: 1085-1089 Awareness during – implications of explicit intraoperative

D. RADOVANOVIC, Z. RADOVANOVIC

Oncology Institute of Vojvodina, Novi Sad (Serbia)

Abstract. – Anaesthesia awareness (AA) that he didn’t feel anything or might have felt is postoperative recall of events experienced un- moderate or intense pain or pressure if the anal- der general anaesthesia. Most frequently pa- gesics dose hadn’t been adequate. tients remember an auditory perception, the feel- It is believed that awareness occurs as a result ing of motor function lost, pain, helplessness, , panic, impending death. The prevalence of auditory and verbal stimuli that are registered of awareness in nonobstetric and noncardiac by brain cortex during the anaesthesia of appar- surgical cases is 0.1%-0.2%. The prevalence is ently adequate depth. Explicit awareness means higher in , obstetric and major that patients are able to express their trauma cases. According to the results of many postoperatively. It occurs spontaneously or after studies light anaesthesia is the most common being provoked by some questions or a postoper- cause of the AA. Posttraumatic stress disorder ative event shortly after operation. With implicit appears in 33%-56% of patients who experi- enced awareness during general anaesthesia. awareness patients are not able to express their Extreme awareness experiences are very un- memories postoperatively and are not aware of common, but traumatic and can have lasting ef- them, but there are changes in performance or fects on patients. Several brain-function moni- behavior that can be proved by hypnosis, specific tors based on the processed electroencephalo- tests and other methods1,2. In 1985, Bennett3 car- gram or evoked potentials have been developed ried out a double-blind study of implicit aware- to assess anaesthetic depth. Measures to pre- vent awareness include avoidance of light anes- ness, in which he randomized 33 patients to ei- thesia, gaining more knowledge about patient ther suggestion or control group. Suggestion anaesthetic requirements and development of group patients were called by their names while methods to detect during anes- they were under anaesthesia and asked to pull thesia. their ear postoperatively. They received , halothane or enflurane. After the operation Key Words: none of the patients could recall the suggestion Anaesthesia general, Anaesthesia depth, Complica- but the patients who had received the message in- tions awareness, Explicit recall. traoperatively were recorded to pull their ears more frequently than patients in the control group.

What do Patients Most often Remember? Most frequently they remember an auditory perception (voices 66%, noises 17%), the feeling Introduction of motor function lost (not being able to breath 48%, sensation of paralysis 17%), pain (38%), Anaesthesia awareness (AA) is postoperative feelings of helplessness, anxiety, panic, impend- recall of events experienced under general anaes- ing death, or catastrophe (34%)4,5. Depending of thesia. This term refers to the situation when we what part of the operation they remember, the cannot assume, on the basis of usual clinical pain can come from intubation, incision or the signs (such as blood pressure increase, heart rate following surgical procedure. frequency, muscular contractions, lacrimation, etc.), that anaesthesia is not of adequate depth. When do Patients Become Aware? After operation patient could remember some or Sandin et al.6 performed one of the largest all events during the surgery and it is possible study on this topic which included 11785 pa-

Corresponding Author: Dragana Radovanović, MD; e-mail: [email protected] 1085 D. Radovanovic, Z. Radovanovic tients. They identified 18 cases of awareness and plicit completely developed, so they are one case of inadvertent muscle blockade that had not able to express their memories. Besides, the occurred before unconsciousness. Prevalence of EEG is changing during the children’s growth, so awareness was 0.18% in cases in which neuro- there is some data showing that the methods for muscular blocking drugs were used, and 0.1% in awareness such as the absence of such drugs. Results showed that (BIS) and entropy, are less reliable in children 39% of patients awareness was identified already younger than one year old ones. in post-anaesthesia care unit (PACU), in 33% of The frequency of AA is not high, but we the patients between the 1st and the 3rd day after shouldn’t forget the great number of various in- the operation and in 27% of the patients aware- terventions that are performed under general ness was detected on the 7th day after the opera- all over the world every day. At issue tion and anaesthesia. Significant percentage of here is a significant number of AA cases. We patients report awareness at PACU but they should have in mind that the presence of aware- negate it during the following checks and vice ness under general anesthesia falls within the versa. The detection of awareness depends on the range of responsibilities of an anaesthesiologist, interview technique, timing of the interview and thus a case of AA can turn into a law suit case structure of the interview7. Therefore, it is neces- against an anaesthesiologist. sary to check the patients who are suspected of being aware under anaesthesia minimum three Risk Factors times, in three different time intervals. Regarding the different kinds of surgical inter- ventions, awareness is more frequent at major Frequency traumas that are followed by hypovolemia and The prevalence of awareness in nonobstetric , cardiac surgeries, C-sections, at in- and noncardiac surgical cases is 0.1%-0.2%2,4,6-8. tervention that are carried out at night, in opera- In a study from Australia, Myles et al8 reported a tion of patient who undergo general anaesthesia frequency of awareness of 0.10%; it was the high- for the first time1,10. est risk factor for patient dissatisfaction after anes- A careful review of the literature reveals that thesia. However, in certain patient groups, such regarding the sex and age as risk factors, results those undergoing anesthesia for cardiac, emer- are very different4,7,16-18. So, in the study which gency trauma, obstetric surgery or bronchoscopy, included 3843 patients in Finland16, awareness an increased risk for awareness and recall has was identified only in female patients, with inci- been reported. The prevalence in cardiac surgery dence of awareness of 0.07% in outpatients and ranges from 1.1-1.5%, in obstetric cases (0.4%) 0.13% in inpatients. On the other side, an Ameri- and major trauma cases (11-43%)1,2,9-14. can study on 177468 patients19 showed that the Studies that have been performed recently prevalence of awareness was two times higher in show that awareness is more common in children male patients of an older age. than in adults, which causes a real problem15. The Table I shows the major and minor criteria There are several reasons for that: it is believed of awareness frequency during general anaesthe- that the children up to third year don’t have ex- sia. The patient with the higher risk for aware-

Table I. Major and minor criteria of awareness incidence during general anaesthesia.

Major criteria Minor criteria

• Preoperative long-term use of anticonvulsant agents, • Use of beta-blockers , , or cocaine • Heavy intake • Chronic obstructive pulmonary disease (COPD) • History of anaesthesia awareness and/or history of • Obesity BMI > 30 difficult intubation • ASA physical status class 4 or class 5 • Smoking two or more packs of cigarettes per day • Cardiac ejection fraction (EF) < 40% • Aortic stenosis • Pulmonary hypertension

1086 Awareness during general anaesthesia – implications of explicit intraoperative recall ness is the one with at least one major risk crite- In particular, according to the results of the rion or two minor risk criteria. research carried out in Spain with 4001 patients It has been suggested that there may be a high- included, the prevalence of awareness in elective er frequency of awareness in obese patients for surgery was 0.6%. The patients were divided into several reasons, including often prolonged time three groups on the basis of anaesthetic tech- for endotracheal intubation, the use of higher nique: the prevalence of awareness was signifi- concentrations of oxygen in nitrous oxide-oxy- cantly higher in patients where inhalation anaes- gen mixtures and the difficulty of giving appro- thetics halogen-containing were not used, the priate doses of drugs without causing postopera- prevalence was 1% for TIVA propofol anaesthe- tive respiratory depression4,16,20. sia (which means 1% out of all patients who got TIVA were aware), 0.59% for balanced anaesthe- 10 Causes (Table II) sia, 5% for O2/N2O . The light anaesthesia was the most common cause of the AA according to results of many Consequences studies2,4,10,13,17,18. Sometimes it is impossible to Posttraumatic stress disorder appears in 33%- avoid inadequate anaesthetic dose: some cases of 56% of patients who experienced awareness dur- emergency procedures, procedures that are car- ing general anaesthesia: depression, anxiety, ried out at night, procedures followed by massive disturbances, , panic attacks blood loss and hemodynamic instability, in pa- may appear even after 2 years and more7,17,22-25. tients with low cardiac reserve. Some patients Extreme awareness experiences are very uncom- need more anaesthetic that can be the cause of mon, but traumatic and can have lasting effects this complication10. Routine administration of on patients. muscle relaxants, especially if they are given be- fore hypnotics as an introduction to anaesthesia, Treatment poor connection between intravenous cannula Includes the following: calming down the pa- and extravascular parts of the aparatusses, empty tient, open discussion about the risk factors for evaporators, evaporators that are not calibrated awareness during general anaesthesia, why and and other causes that may consequently result in how often it happens, the necessity of informing an inadequate delivery of anaesthetic1,2,7. the anaesthesiologist about the problem before Regarding the anaesthetic technique, it should the next anesthesia, offering an apology and ex- be considered wheather it affects the frequency planation. In some institutions it is openly dis- of awareness. The results of some studies show cussed with patients before surgical interventions that the frequency of awareness is higher when about the possible awareness episodes during the total IV anesthesia (TIVA) technique is used anaesthesia. It hasn’t been proved if such discus- compared with balanced technique. However, sions can psychologically influence the increased with TIVA, it’s impossible to monitor the con- number of cases of anaesthesia awareness report- centration of i.v. agents in the blood. On the oth- ed by the patients1. er hand, with inhalation anesthesia, it is possible to monitor the N2O level and volatile anaesthetics Modern Monitoring in expiratory air10,21. Several brain-function monitors based on the processed electroencephalogram or evoked po- tentials have been developed to assess anaesthet- Table II. Causes of anaesthesia awareness. ic depth. Results of few investigations suggested that BIS reduced anaesthetic use, recovery times, • Inadequate anaesthetic dose – emergency trauma, risk of awareness and cost9,26,27. Findings in study hypovolemic patients, emergency C-section, cardiac by Avidan do not support routine BIS monitoring surgery as part of standard monitoring. According to re- • Resistance to anaesthetics – hyperthyroidism, obesity, sults of this study AA occurred even when BIS anxiety, younger age, long-term use of certain drugs (alcohol, opiates or ) values and end-tidal gas (ETAG) con- centrations were within the target ranges; the use • Routine administration of muscle relaxants of the BIS protocol was not associated with re- • Mechanical malfunction or misuse of duced administration of volatile anaesthetic gas- • Anaesthetic technique? es. It is important to emphasize that the BIS monitoring may be useful during total intra-

1087 D. Radovanovic, Z. Radovanovic venous anaesthesia, since it is not presently pos- Consultants who participated in ASA Practice sible to monitor the blood concentrations of advisory for intraoperative awareness strongly anaesthetic agents28. agree that functioning of anaesthesia delivery We can conclude that the clinical monitoring systems (e.g., vaporizers, infusion pumps, fresh of patients is an irreplaceable and necessary pro- gas flow, intravenous lines) should be checked to cedure in interpretation of the results coming reduce the risk of intraoperative awareness. Mon- with modern monitoring. itoring of the concentrations of inspired and ex- pired gases and inhalation agents; and general How to Avoid Anesthesia Awareness? vigilance should eliminate cases caused by inad- (Table III) equate anaesthetic delivery1,2. In high risk situa- We should preoperatively consider if there is a tions, monitoring of depth of anaesthesia is justi- higher risk for anaesthesia awareness and inform fied. Use of such monitoring may also be advis- selected patients of the possibility of intraopera- able in patients in whom clinical signs of light tive awareness. The American Society of Anes- anaesthesia may be masked (concurrent β-block- thesiologists (ASA) has published guidelines rec- ers, diabetes). ommended that stringent efforts must be made to Awareness during anaesthesia is uncommon, prevent AA1. but well described adverse outcome that may re- We should consider premedication with sult in serious emotional injury and post-traumat- amnestic agents. The results of some studies ic stress disorder. A properly trained anaesthetist, show that the application of benzodiazepines re- administering anaesthesia according to knowl- duces the incidence of awareness10,29. There was edge of pharmacology and patient and surgical no difference in the frequency of awareness and characteristics, assisted by clinical signs and recall in respect to premedication, according to monitoring, can minimize the risk of awareness. the results of Sandin et al. study6. This observa- Measures to prevent awareness include avoid- tion seems to agree with the suggestion of a mi- ance of light anesthesia, gaining more knowledge nor role of premedication in pro- about anaesthetic requirements of patients and tection from awareness and recall during anaes- development of methods to detect consciousness thesia6,16. Any firm conclusion about the effect of during anesthesia. benzodiazepines on the frequency of awareness and recall should be drawn cautiously, because the timing of the administration in relation to the operation is not standardized, and the duration of References surgery varied considerably. 1) Practice advisory for intraoperative awareness and brain functioning monitoring: A report by the Table III. How to avoid anaesthesia awareness? American Society of Anesthesiologists Task Force on Intraoperative Monitoring. Anesthesiolo- • Consider if there is a higher risk for AA preoperatively gy 2006; 104: 847-864. • Consider premedication with amnestic agents? 2) GHONEIM MM. Awareness during anesthesia. • Ensure patient is asleep prior to intubation 2000; 92: 597-602. • Provide additional doses of hypnotic or volatile agent 3) BENNETT HL. Non-verbal response to intraoperative for repeated intubation attempts conversation. Br J Anaesth 1985; 57: 174-179.

• Avoid paralysis unless needed 4) GHONEIM MM, BLOCK RI, HAFFARNAN M, MATHEWS MJ. • Use an end-Tidal agent monitor Awareness during anesthesia: risk factors, caus- • Give adequate doses of anaesthetic agents – administer es and sequelae: A Review of reported cases in at least 0,8-1 minimum alveolar concentration (MAC) the literature. Anesth Analg 2009; 108: 527-535. when volatile agents are used alone 5) SCHWENDER D, KUNZE-KRONAWITTER H, DIETRISH P, K LAS- • Check all anaesthesia equipment: anaesthesia machine, ING S, FORST H, MADLER C. Conscious awareness vaporizer, infusion pumps during general anaesthesia: patients’ perceptions, • Pay more attention on possible awareness when use emotions, cognition and reactions. Br J Anaesth β-blockers 1998; 80: 133-139. • Be careful about the discussion in the surgical room 6) SANDIN RH, ENLUND G, SAMUELSSON P, L ENNMARKEN C. • Patients with high risk for awareness consider use of Awareness during anaesthesia: a prospective brain function monitoring case study. Lancet 2000; 355: 707-711.

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