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Despite advances in anesthetic technique and technology, intraoperative awareness continues to occur with alarming regularity. The psychological effects on patients and the medicolegal consequences to providers have created the need for a reliable monitor of the hypnotic component of anesthesia. A new technology known as bispectral analysis (BIS) has the potential to put an end to the devastating occurrence of intraoperative awareness, as well as improve the overall effectiveness of anesthetic delivery and the surgical experience. Applicable to almost any situation requiring sedation or general anesthesia, BIS's reliability is a real-time measure of hypnosis levels.
PURPOSE OF REVIEW: This review will outline old and recent data about the prevalence, causes and potential consequences of intraoperative awareness in children and give details on its detection. RECENT FINDINGS: Recent studies have confirmed the higher incidence of intraoperative awareness in children than in adults while using modern anaesthetic techniques. To detect this complication in children, the Brice interview, commonly used in adults, has to be adapted to children's cognitive capacities, with an extended follow-up. Neither the old nor the recent studies clearly identify predictive risk factors. Children describe the same perceptions as adults during their awareness period (mainly auditory and tactile sensations), but with fewer negative thoughts. Moreover, they do not seem to be affected by this experience, as they do not have long-term psychological sequelae. The prevention of intraoperative awareness in children is the same as in adults, the major factor being awareness of this complication. SUMMARY: Intraoperative awareness is a reality in school-aged children. A larger multicentre study and large-scale follow-up is required in order to confirm the higher incidence of awareness and identify the risk factors and long-term psychological sequelae of this complication in the paediatric population.
STUDY OBJECTIVE: To determine how much patients are willing to pay to avoid intraoperative awareness? DESIGN: Observational study SETTING: University-affiliated metropolitan hospital. PATIENTS: 60 patients who completed a questionnaire (39 F, 21 M). The mean age was 43 years and the median household income range of 45,000-60,000 US dollars. INTERVENTIONS: Patients completed an interactive computer-generated questionnaire on the value of preventing intraoperative awareness and their willingness to pay for a "depth of anesthesia" monitor. Their willingness to pay for the prevention of postoperative pain, nausea and vomiting, postoperative grogginess, and sleepiness was also determined as a means of comparison. MEASUREMENTS AND MAIN RESULTS: Patients were willing to pay (WTP) 34 US dollars, 10 US dollars to 42 US dollars (median, interquartile range) for a monitor that would assist an anesthesia care provider assess the depth of anesthesia in an effort to avoid awareness. This increased to 43 US dollars, 20 US dollars to 77 US dollars (p < 0.0,001) (median, interquartile range), if the insurance company was making the payment and the WTP value only decreased minimally to 33 US dollars if the incidence of awareness was reduced 10-fold. CONCLUSION: The incidence of intraoperative awareness and WTP value for monitoring awareness have a nonlinear relationship (a risk averse utility function), which suggests that patients assign an intrinsic base value for a rare or very rare possibility of an event. Other healthcare economic analyses (such as cost effectiveness) do not take this factor into account and assume a linear value relationship (i.e., if something occurs ten times less frequently, it has ten times less value). IMPLICATION: The median value for patients' WTP for a monitor that might prevent awareness under anesthesia was 34 US dollars given an incidence of 5/1,000 cases. The incidence of awareness and WTP value have a nonlinear relationship suggesting that patients assign an intrinsic base value for the possibility of awareness.
Midlatency auditory evoked potentials (MLAEP) are suppressed dose-dependently during anaesthesia with a variety of general anaesthetics. Therefore, MLAEP have been proposed to measure depth of anaesthesia and to indicate intraoperative awareness. Several studies give evidence of a close relationship between MLAEP and motor signs of wakefulness, intraoperative awareness, and explicit and implicit memory functions during general anaesthesia. Summarising these data, one may conclude that there is a close hierarchical relation between cognitive function, memory and wakefulness during anaesthesia, and MLAEP latencies. A short Nb latency below 45 ms is consistent with conscious awareness and unimpaired memory function with explicit recall and adequate response to commands. When Nb latency increases to 45-50 ms, it may be associated with conscious awareness. Patients still respond to commands, but memory formation is impaired and explicit recall is lost. A further increase of Nb latencies seems to be consistent with unconscious awareness, characterised by implicit memory of intraoperative events; 60 ms seems to be the threshold value for motor signs of wakefulness during anaesthesia. With a further increase of MLAEP latency during anaesthesia, conscious awareness and memory formation, explicit and implicit recall, response to commands, and spontaneous purposeful movements during anaesthesia are blocked. The new volatile anaesthetic sevoflurane leads to a dose-dependent increase in MLAEP peak latencies and a decrease in MLAEP amplitudes. At about 1.5 vol.% end-expiratory sevoflurane concentration, MLAEP are significantly suppressed and Nb latency is in the range of 68-80 ms. Therefore, from the present data and those from the literature, one may expect that sevoflurane at concentrations greater than 1.5 vol.% for general anaesthesia would be able to suppress awareness phenomena such as purposeful movements, auditory perception, intraoperative wakefulness and awareness, memory formation, and explicit and implicit recall of intraoperative events.
The first cases of general anesthesia were already cases with awareness. Until today, case reports of patients with awareness are published. These published cases are likely to be the top of the iceberg, as most patients with postoperative recall do not inform their anesthesiologist. Incidence of awareness with recall is between 0.1 and 0.2 %. In a large multicenter-study, incidence of recall was 0.1 % without, and 0.18 % with the use of muscle relaxants. The risk is increased with decreased doses of anesthetics, e.g. in patients with hemodynamic instability (trauma cases), patients undergoing cesarean section or cardiac surgery. Intraoperative awareness does not necessarily cause explicit (conscious) memory. Even in the absence of explicit memory, implicit (unconscious) memory can still have consequences for the patient. In the worst case, it can cause post-traumatic stress disorder. There is doubt whether patients may profit from positive suggestions given during intraoperative awareness. Recommendations to administer benzodiazepines to prevent explicit memory must be reconsidered. Complete neuromuscular block should be avoided whenever possible. If a patient is thought to be aware, he should be contacted, his situation should be explained and affirming comments should be given until consciousness is lost again. Postoperative visit should include questions about awareness and recall. The anesthetist should not disbelieve reported recall. Explanation of what had happened and referral to an experienced psychologist must be offered. Thus, the incidence of severe sequelae should decrease.
A case of intraoperative awareness during a thoracotomy is described. The patient's recall coincided with an intraoperative period during which a Siemens 900B ventilator and a Siemens 952 isoflurane vaporiser were used. Subsequent assessment of this equipment with an anaesthetic agent analyzer revealed that, at the ventilator settings which had been used, the delivered anaesthetic vapour concentration varied greatly from the vaporizer settings. This problem eventually was traced to a malfunctioning inlet control valve on the ventilator. This complication may have been prevented if the end-tidal anaesthetic concentration had been monitored intraoperatively.
We experienced two cases of intraoperative awareness during intravenous anesthesia with propofol and fentanyl in morbidly obese patients. The rates of propofol infusion were calculated according to the adjusted body weights, or reduced intentionally as obese patients are generally believed to require lower doses of propofol compared with non-obese patients. Our postoperative analysis by simulations using the anesthesia records showed that, when the simulation was based on real body weight, the blood/effect-site concentrations of propofol in both patients would have been below the necessary levels to keep the patients unconscious during the operation, but when the simulation was based on adjusted body weight, those concentrations might have been within the necessary range to maintain an adequate hypnotic level. We propose that the rate of propofol infusion should be the same in obese and non-obese patients and should be calculated according to the real body weight not to the adjusted body weight.
PURPOSE: The aim of this clinical report is to describe a case of unintentional intraoperative awareness during sufentanil anaesthesia in a patient undergoing elective aortocoronary bypass grafting. CLINICAL FINDINGS: After premedication with morphine (5 mg) and scopolamine (0.2 mg), this 51-yr-old woman received sufentanil (10 micrograms.kg-1), midazolam (4 mg) and isoflurane (0.3-0.4% end-tidal). The patient recalled specific events and discussions which took place in the operating room during surgery. This patient's report was clear and corroborated by operating room personnel. The patient denied having felt pain, anxiety or emotional distress. CONCLUSION: Although awareness during opioid anaesthesia has been previously described with morphine and fentanyl, as far as we know this is the first clinical report of awareness with sufentanil. Given that recent efforts of early extubation in cardiac surgery patients may involve a reduction in the amount of opioid administered, this report serves as a reminder of the ever present potential for this disturbing complication.
We have reviewed randomized controlled trials to assess the effectiveness and safety of anaesthetics which omitted nitrous oxide (N2O) to prevent postoperative nausea and vomiting (PONV). Early and late PONV (6 and 48 h after operation, respectively), and adverse effects were evaluated using the numbers-needed-to-treat (NNT) method. In 24 reports with information on 2478 patients, the mean incidence of early and late vomiting with N2O (control) was 17% and 30%, respectively. Omitting N2O significantly reduced vomiting compared with a N2O regimen; the combined NNT to prevent both early and late vomiting with a N2O-free regimen was about 13 (95% confidence intervals (CI) 9, 30). The magnitude of the effect depended on the incidence of vomiting in controls. In studies with a baseline risk higher than the mean of all reports, the NNT to prevent both early and late vomiting with a N2O-free anaesthetic was 5 (95% CI 4, 10). When the baseline risk was lower than the mean, omitting N2O did not improve outcome. Omitting N2O had no effect on complete control of emesis or nausea. The NNT for intraoperative awareness with a N2O-free anaesthetic was 46 compared with anaesthetics where N2O was used. This clinically important risk of major harm reduces the usefulness of omitting N2O to prevent postoperative emesis.
The authors base their remark on a few cases of awareness which have been reported in their hospital and on the history a patient who experienced intraoperative awareness during cesarean section. Attention is focused on the ethical, social and medico-legal aspects of this phenomenon. Awareness may severely affect the patient's psychic equilibrium with the consequent onset of severe neuroses leading to the possibility of legal action and claims for compensation. Clinical experience has shown that the use of halogenate anesthetics, even in low concentrations, may help to avoid this phenomenon. Correct relations between the anesthetist and patient before and after surgery may also, even in the event of awareness, reduce the incidence and severity of consequent psychological sequelae.
Since the first case report by Winter-bottom [106], the problem of intraoperative awareness or recall has received increasing attention from patients, anaesthesiologists and, more recently, even law courts [4, 20, 21, 78]. Our own interest in awareness derives from a study with the opiate agonist tramadol as a supplement to balanced anaesthesia, which revealed an unexpectedly high incidence of about 65% of patients who could recall intraoperative music [55]. It was the aim of the present randomized double-blind study to evaluate, under identical experimental conditions, what the incidence would be with other analgesic supplements to balanced anaesthesia (fentanyl, pentazocine and ketamine). Because few reports on this subject are available in the German literature, it was felt that the result should be discussed within a comprehensive review. PATIENTS AND METHODS. A total of 60 patients (ASA I-II, age 27-66 years, weight 48-93 kg) undergoing elective gynaecological surgery of at least 90 min duration were each randomly assigned to one of three study groups (F, fentanyl; P, pentazocine; K, ketamine). Premedication was performed with diazepam 10 mg p.o. the evening before surgery and pethidine 1 mg/kg i.m.+promethazine 1.5 mg/kg i.m.+atropine 0.5 mg i.m. 60 min before anaesthesia. Induction was performed with alcuronium (2 + 8 mg), methohexital (1.5 mg/kg) and a bolus dose of the analgesic supplement (F, 5 micrograms/kg; P or K, 2 mg/kg), followed by continuous infusion (F, 2 micrograms kg-1 h-1, P or K 0.8 mg kg-1 h-1). Endotracheal intubation was performed with succinylcholine (1 mg/kg). Patients were ventilated to normocarbia using a Takaoka respirator (4 breaths/min, tidal volume 1600 ml, N2O/O2 75:25). If insufficient anaesthesia was suggested by increases in blood pressure or heart rate to more than 20% of preinduction values, excessive sweating or lacrimation, enflurane (0.5-2 vol.%) was added for short periods of time. At the end of surgery, patients were ventilated with 100% O2, and the neuromuscular block antagonized using atropine 0.5 mg and neostigmine 1 mg. Without prior announcement, tape-recorded music (Mantovani, 3 min followed by 3 min silence) was played to all patients via earphones throughout the time period between intubation and the end of nitrous oxide administration. Vegetative parameters, cumulative and relative enflurane application times and retrospective judgement of quality of anaesthesia by the anaesthesiologist were documented. Post-operative recovery and pain were monitored using verbal rating scales. Patients were interviewed immediately after extubation and on the day after surgery to determine the incidence of dreams and recollection of music. Patients were classified as amnestic if they could not recall the music, even with prompting, and partially amnestic if they remembered the music but were unable to define the time when they had heard it. No amnesia was assumed if patients recalled the intraoperative music spontaneously. Groups were statistically compared by means of analysis of variance, Mann-Wilcoxon rank sum test and chi-square test. RESULTS. Mean duration of anaesthesia was 129-134 min in the subgroups. The total analgesic supplement dose was F 614 +/- 129 micrograms, P 238 +/- 38 mg, and K 230 +/- 50 mg (mean +/- SD). Enflurane substitution was necessary in 45 patients, regardless of the type of analgesic supplement. Mean cumulative enflurane application time was 26-28% in the treatment groups, corresponding to about 20% of anaesthesia duration. The most important reasons for enflurane substitution were increases in blood pressure (mostly in groups F and P) or heart rate (K). Recovery was fastest with F, followed by P, and slowest with K. Retrospective judgement of the quality of anaesthesia by the anaesthesiologist did not differ significantly between the treatment groups. Most (93%) of the patients were satisfied with their anaesthesia; 2 patients each who received P and K were dis
Intraoperative wakefulness is not only limited to adults and can also be found at a similar percentage (0.8%) in paediatric anaesthesia. For prevention of awareness neurophysiologic methods like auditory evoked potentials might be helpful. We report a case of a 2-year-old boy receiving balanced anaesthesia with sevoflurane and alfentanil. Midlatency auditory evoked potentials (MLAEPs) were recorded continuously before, during and after the surgical procedure. During the surgical procedure sevoflurane was withdrawn unintentionally. After a short period of time the boy started coughing and moved his legs, which was interpreted as insufficient analgesia. Several boli of alfentanil did not lead to the expected clinical effect on the depth of anaesthesia. After a recheck of the anaesthetic ventilator the error was determined and delivery of the volatile anaesthetic restored. The postoperative evaluation of the MLAEPs revealed the inadequate suppression of auditory processing during this incident with latencies comparable to the awake state. After reapplication of sevoflurane the MLAEPs were almost completely suppressed demonstrating adequate anesthetic depth. Exemplarily this case suggests that MLAEPs could be used to detect intraoperative awareness also in paediatric anaesthesia. Investigations to prove the validity and reproducibility of MLAEPs in children will be necessary.
This report describes a case of awareness and recall during propofol anesthesia combined with epidural anesthesia in a 32-year-old woman scheduled for a resection of left ovarian tumor. After induction, anesthesia was maintained with propofol and epidural anesthesia. About one hour into maintenance, the patient was moving with haemodynamic signs suggesting inadequate analgesia. Immediately after extubation, the patient could recall the abdomen being touched during laparotomy. This case indicates that even if appropriate dose of propofol is administrated, intraoperative awareness may occur especially with inadequate analgesia.
BACKGROUND: Fast-track cardiac anesthesia, using low-dose narcotics combined with short-acting anesthetic and sedative agents, facilitates early tracheal extubation after cardiac surgery. The incidence of awareness with this anesthetic technique has not been investigated previously. The purpose of this study was to prospectively investigate the incidence of intraoperative awareness with explicit memory of events during fast-track cardiac anesthesia. METHODS: Data were collected prospectively over a 4-month period from 617 consecutive adult patients undergoing cardiac surgery at a university hospital. All patients received a fast-track cardiac anesthetic regimen. Patients underwent a structured interview by a research nurse 18 h after extubation. A standard set of questions was asked during this interview to determine if the patient had explicit memory of any event from induction of anesthesia to recovery of consciousness. RESULTS: Nine patients did not complete a postoperative interview because of death (n = 7) or postoperative confusion (n = 2). The last memory before surgery reported in 420 (69.1%) patients was waiting in the holding area at the operating suite, and in the remaining 188 (30.9%) patients it was lying on the operating table before induction of anesthesia. Two patients (0.3%) had explicit memory of intraoperative events. One of the two patients also had explicit memory of pain. Neither patient reported adverse psychological sequelae. CONCLUSIONS: The authors report an incidence of awareness in fast-track cardiac anesthesia of 0.3%. This is the lowest incidence of awareness currently reported during cardiac surgery. This low incidence of awareness may be related to the use of a balanced anesthetic technique involving the continuous administration of volatile (isoflurane) or intravenous (propofol) anesthetic agents before, during, and after cardiopulmonary bypass.
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Several methods have been developed to quantify central anaesthetic effects and monitor awareness during general anaesthesia. The most important of these are the PRST score, calculated from changes in blood pressure, heart rate, sweating, and tear production, the isolated forearm technique, where the patient is allowed to move during surgery, the processed electroencephalogram (EEG) and the derived parameters median frequency (MF) and spectral-edge frequency (SEF), and mid-latency auditory evoked potentials (MLAEP). In clinical practice, the application of individual doses of anaesthetics is generally guided by autonomic vegetative clinical signs such as changes in blood pressure, heart rate, sweating, and tear production, quantified as the PRST score. Unfortunately, these parameters are not very reliable with regard to predicting the suppression of consciousness and awareness, especially when high-dose opioids are used in patients with cardiovascular medications and a variety of accompanying diseases. The PRST score probably indicates mainly the autonomic responses to painful stimuli, and seems to be useful in guiding the individual use of analgesics. The isolated forearm technique is a useful test of the patient's responsiveness during general anaesthesia, and thus an instrument for investigating the incidence of awareness during different anaesthetic regimens and when muscle relaxants are employed. A disadvantage is that it can only be used for 20 to 30 min because of pressure-induced nerve blocks or lesions. It can not be employed when long-term relaxation is necessary and consciousness and awareness are to be monitored continuously. The processed EEG and the derived parameters MF and SEF are important scientific tools to quantify central effects of many anaesthetics and opioid analgesics that allow the development of pharmacodynamic-pharmacokinetic models of anaesthetic action. MF has proven to be useful in monitoring closed-loop feedback of intravenous drug administration. Unfortunately, until now there have been no clinical studies that document the usefulness of MF or SEF with regard to predicting intraoperative arousal or awareness. To the contrary, some experimental data failed to predict imminent arousal and response to surgical incision or verbal commands by MF or SEF. Therefore, the EEG seems to be of limited value for monitoring awareness, consciousness, or memory formation during anaesthesia. MLAEP are suppressed in a dose-dependent fashion by many general anaesthetics and correlate with wakefulness, awareness, and explicit and implicit memory during anaesthesia and seem to be a promising method of monitoring awareness during anaesthesia. Nevertheless, future studies will have to determine threshold values for the different MLAEP parameters for intraoperative awareness and explicit and implicit recall of intraoperatively presented information for the different commonly used anaesthetics. Only then will it be possible to determine the usefulness of the method in clinical practice.