awareness during general anaesthesia. implications of explicit intraoperative recall

Transcription

1 European Review for Medical and Pharmacological Sciences Awareness during general anaesthesia implications of explicit intraoperative recall D. RADOVANOVIC, Z. RADOVANOVIC Oncology Institute of Vojvodina, Novi Sad (Serbia) 2011; 15: Abstract. Anaesthesia awareness (AA) is postoperative recall of events experienced under general anaesthesia. Most frequently patients remember an auditory perception, the feeling of motor function lost, pain, helplessness, anxiety, panic, impending death. The prevalence of awareness in nonobstetric and noncardiac surgical cases is 0.1%-0.2%. The prevalence is higher in cardiac surgery, obstetric and major trauma cases. According to the results of many studies light anaesthesia is the most common cause of the AA. Posttraumatic stress disorder appears in 33%-56% of patients who experienced awareness during general anaesthesia. Extreme awareness experiences are very uncommon, but traumatic and can have lasting effects on patients. Several brain-function monitors based on the processed electroencephalogram or evoked potentials have been developed to assess anaesthetic depth. Measures to prevent awareness include avoidance of light anesthesia, gaining more knowledge about patient anaesthetic requirements and development of methods to detect consciousness during anesthesia. Key Words: Anaesthesia general, Anaesthesia depth, Complications awareness, Explicit recall. Introduction Anaesthesia awareness (AA) is postoperative recall of events experienced under general anaesthesia. This term refers to the situation when we cannot assume, on the basis of usual clinical signs (such as blood pressure increase, heart rate frequency, muscular contractions, lacrimation, etc.), that anaesthesia is not of adequate depth. After operation patient could remember some or all events during the surgery and it is possible that he didn t feel anything or might have felt moderate or intense pain or pressure if the analgesics dose hadn t been adequate. It is believed that awareness occurs as a result of auditory and verbal stimuli that are registered by brain cortex during the anaesthesia of apparently adequate depth. Explicit awareness means that patients are able to express their memories postoperatively. It occurs spontaneously or after being provoked by some questions or a postoperative event shortly after operation. With implicit awareness patients are not able to express their memories postoperatively and are not aware of them, but there are changes in performance or behavior that can be proved by hypnosis, specific tests and other methods 1,2. In 1985, Bennett 3 carried out a double-blind study of implicit awareness, in which he randomized 33 patients to either suggestion or control group. Suggestion group patients were called by their names while they were under anaesthesia and asked to pull their ear postoperatively. They received nitrous oxide, halothane or enflurane. After the operation none of the patients could recall the suggestion but the patients who had received the message intraoperatively 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 of motor function lost (not being able to breath 48%, sensation of paralysis 17%), pain (38%), feelings of helplessness, anxiety, panic, impending death, or catastrophe (34%) 4,5. Depending of what part of the operation they remember, the pain can come from intubation, incision or the following surgical procedure. When do Patients Become Aware? Sandin et al. 6 performed one of the largest study on this topic which included pa- Corresponding Author: Dragana Radovanović, MD; dsakic@eunet.rs 1085

2 D. Radovanovic, Z. Radovanovic Risk Factors Regarding the different kinds of surgical interventions, awareness is more frequent at major traumas that are followed by hypovolemia and hypotension, cardiac surgeries, C-sections, at intervention that are carried out at night, in operation of patient who undergo general anaesthesia for the first time 1,10. A careful review of the literature reveals that regarding the sex and age as risk factors, results are very different 4,7, So, in the study which included 3843 patients in Finland 16, awareness was identified only in female patients, with incidence of awareness of 0.07% in outpatients and 0.13% in inpatients. On the other side, an American study on patients 19 showed that the prevalence of awareness was two times higher in male patients of an older age. The Table I shows the major and minor criteria of awareness frequency during general anaesthesia. The patient with the higher risk for awaretients. They identified 18 cases of awareness and one case of inadvertent muscle blockade that had occurred before unconsciousness. Prevalence of awareness was 0.18% in cases in which neuromuscular blocking drugs were used, and 0.1% in the absence of such drugs. Results showed that 39% of patients awareness was identified already in post-anaesthesia care unit (PACU), in 33% of the patients between the 1 st and the 3 rd day after the operation and in 27% of the patients awareness was detected on the 7 th day after the operation and anaesthesia. Significant percentage of patients report awareness at PACU but they negate it during the following checks and vice versa. The detection of awareness depends on the interview technique, timing of the interview and structure of the interview 7. Therefore, it is necessary to check the patients who are suspected of being aware under anaesthesia minimum three times, in three different time intervals. Frequency The prevalence of awareness in nonobstetric and noncardiac surgical cases is 0.1%-0.2% 2,4,6-8. In a study from Australia, Myles et al 8 reported a frequency of awareness of 0.10%; it was the highest risk factor for patient dissatisfaction after anesthesia. However, in certain patient groups, such those undergoing anesthesia for cardiac, emergency trauma, obstetric surgery or bronchoscopy, an increased risk for awareness and recall has been reported. The prevalence in cardiac surgery ranges from %, in obstetric cases (0.4%) and major trauma cases (11-43%) 1,2,9-14. Studies that have been performed recently show that awareness is more common in children than in adults, which causes a real problem 15. There are several reasons for that: it is believed that the children up to third year don t have ex- plicit memory completely developed, so they are not able to express their memories. Besides, the EEG is changing during the children s growth, so there is some data showing that the methods for monitoring awareness such as bispectral index (BIS) and entropy, are less reliable in children younger than one year old ones. The frequency of AA is not high, but we shouldn t forget the great number of various interventions that are performed under general anesthesia all over the world every day. At issue here is a significant number of AA cases. We should have in mind that the presence of awareness under general anesthesia falls within the range of responsibilities of an anaesthesiologist, thus a case of AA can turn into a law suit case against an anaesthesiologist. 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 opiates, benzodiazepines, or cocaine Heavy alcohol 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

3 Awareness during general anaesthesia implications of explicit intraoperative recall Modern Monitoring Several brain-function monitors based on the processed electroencephalogram or evoked potentials have been developed to assess anaesthetic depth. Results of few investigations suggested that BIS reduced anaesthetic use, recovery times, risk of awareness and cost 9,26,27. Findings in study by Avidan do not support routine BIS monitoring as part of standard monitoring. According to results of this study AA occurred even when BIS values and end-tidal anesthetic gas (ETAG) concentrations were within the target ranges; the use of the BIS protocol was not associated with reduced administration of volatile anaesthetic gases. It is important to emphasize that the BIS monitoring may be useful during total intraness is the one with at least one major risk criterion or two minor risk criteria. It has been suggested that there may be a higher frequency of awareness in obese patients for several reasons, including often prolonged time for endotracheal intubation, the use of higher concentrations of oxygen in nitrous oxide-oxygen mixtures and the difficulty of giving appropriate doses of drugs without causing postoperative respiratory depression 4,16,20. Causes (Table II) The light anaesthesia was the most common cause of the AA according to results of many studies 2,4,10,13,17,18. Sometimes it is impossible to avoid inadequate anaesthetic dose: some cases of emergency procedures, procedures that are carried out at night, procedures followed by massive blood loss and hemodynamic instability, in patients with low cardiac reserve. Some patients need more anaesthetic that can be the cause of this complication 10. Routine administration of muscle relaxants, especially if they are given before hypnotics as an introduction to anaesthesia, poor connection between intravenous cannula and extravascular parts of the aparatusses, empty evaporators, evaporators that are not calibrated and other causes that may consequently result in an inadequate delivery of anaesthetic 1,2,7. Regarding the anaesthetic technique, it should be considered wheather it affects the frequency of awareness. The results of some studies show that the frequency of awareness is higher when total IV anesthesia (TIVA) technique is used compared with balanced technique. However, with TIVA, it s impossible to monitor the concentration of i.v. agents in the blood. On the other hand, with inhalation anesthesia, it is possible to monitor the N 2 O level and volatile anaesthetics in expiratory air 10,21. Table II. Causes of anaesthesia awareness. Inadequate anaesthetic dose emergency trauma, hypovolemic patients, emergency C-section, cardiac surgery Resistance to anaesthetics hyperthyroidism, obesity, anxiety, younger age, long-term use of certain drugs (alcohol, opiates or amphetamines) Routine administration of muscle relaxants Mechanical malfunction or misuse of anaesthetic machine Anaesthetic technique? In particular, according to the results of the research carried out in Spain with 4001 patients included, the prevalence of awareness in elective surgery was 0.6%. The patients were divided into three groups on the basis of anaesthetic technique: the prevalence of awareness was significantly higher in patients where inhalation anaesthetics halogen-containing were not used, the prevalence was 1% for TIVA propofol anaesthesia (which means 1% out of all patients who got TIVA were aware), 0.59% for balanced anaesthesia, 5% for O 2 /N 2 O 10. Consequences Posttraumatic stress disorder appears in 33%- 56% of patients who experienced awareness during general anaesthesia: depression, anxiety, sleep disturbances, nightmares, panic attacks may appear even after 2 years and more 7,17, Extreme awareness experiences are very uncommon, but traumatic and can have lasting effects on patients. Treatment Includes the following: calming down the patient, open discussion about the risk factors for awareness during general anaesthesia, why and how often it happens, the necessity of informing the anaesthesiologist about the problem before the next anesthesia, offering an apology and explanation. In some institutions it is openly discussed with patients before surgical interventions about the possible awareness episodes during the anaesthesia. It hasn t been proved if such discussions can psychologically influence the increased number of cases of anaesthesia awareness reported by the patients

4 D. Radovanovic, Z. Radovanovic venous anaesthesia, since it is not presently possible to monitor the blood concentrations of anaesthetic agents 28. We can conclude that the clinical monitoring of patients is an irreplaceable and necessary procedure in interpretation of the results coming with modern monitoring. How to Avoid Anesthesia Awareness? (Table III) We should preoperatively consider if there is a higher risk for anaesthesia awareness and inform selected patients of the possibility of intraoperative awareness. The American Society of Anesthesiologists (ASA) has published guidelines recommended that stringent efforts must be made to prevent AA 1. We should consider premedication with amnestic agents. The results of some studies show that the application of benzodiazepines reduces the incidence of awareness 10,29. There was no difference in the frequency of awareness and recall in respect to premedication, according to the results of Sandin et al. study 6. This observation seems to agree with the suggestion of a minor role of benzodiazepine premedication in protection from awareness and recall during anaesthesia 6,16. Any firm conclusion about the effect of 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 surgery varied considerably. Table III. How to avoid anaesthesia awareness? Consider if there is a higher risk for AA preoperatively Consider premedication with amnestic agents? Ensure patient is asleep prior to intubation Provide additional doses of hypnotic or volatile agent for repeated intubation attempts Avoid paralysis unless needed Use an end-tidal agent monitor Give adequate doses of anaesthetic agents administer at least 0,8-1 minimum alveolar concentration (MAC) when volatile agents are used alone Check all anaesthesia equipment: anaesthesia machine, vaporizer, infusion pumps Pay more attention on possible awareness when use β-blockers Be careful about the discussion in the surgical room Patients with high risk for awareness consider use of brain function monitoring Consultants who participated in ASA Practice advisory for intraoperative awareness strongly agree that functioning of anaesthesia delivery systems (e.g., vaporizers, infusion pumps, fresh gas flow, intravenous lines) should be checked to reduce the risk of intraoperative awareness. Monitoring of the concentrations of inspired and expired gases and inhalation agents; and general vigilance should eliminate cases caused by inadequate anaesthetic delivery 1,2. In high risk situations, monitoring of depth of anaesthesia is justified. Use of such monitoring may also be advisable in patients in whom clinical signs of light anaesthesia may be masked (concurrent β-blockers, diabetes). Awareness during anaesthesia is uncommon, but well described adverse outcome that may result in serious emotional injury and post-traumatic stress disorder. A properly trained anaesthetist, administering anaesthesia according to knowledge of pharmacology and patient and surgical characteristics, assisted by clinical signs and monitoring, can minimize the risk of awareness. Measures to prevent awareness include avoidance of light anesthesia, gaining more knowledge about anaesthetic requirements of patients and development of methods to detect consciousness during anesthesia. References 1) Practice advisory for intraoperative awareness and brain functioning monitoring: A report by the American Society of Anesthesiologists Task Force on Intraoperative Monitoring. Anesthesiology 2006; 104: ) GHONEIM MM. Awareness during anesthesia. Anesthesiology 2000; 92: ) BENNETT HL. Non-verbal response to intraoperative conversation. Br J Anaesth 1985; 57: ) GHONEIM MM, BLOCK RI, HAFFARNAN M, MATHEWS MJ. Awareness during anesthesia: risk factors, causes and sequelae: A Review of reported cases in the literature. Anesth Analg 2009; 108: ) SCHWENDER D, KUNZE-KRONAWITTER H, DIETRISH P, K LAS- ING S, FORST H, MADLER C. Conscious awareness during general anaesthesia: patients perceptions, emotions, cognition and reactions. Br J Anaesth 1998; 80: ) SANDIN RH, ENLUND G, SAMUELSSON P, LENNMARKEN C. Awareness during anaesthesia: a prospective case study. Lancet 2000; 355:

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