Awareness during anaesthesia: a review.

Following the introduction of muscle relaxants into anaesthesia there became recognised a state in which patients may be aware of their surroundings but unable to communicate their plight. This state of awareness is more likely to occur during light inhalational or total intravenous anaesthesia. Detection of awareness is difficult and several methods have been described. Measurement of the depth of anaesthesia is also difficult as clinical signs are unreliable and even sophisticated monitoring equipment is unhelpful. Awareness can occur without patient recall and may be due to equipment failure or anaesthetic failure. The former is avoidable and the latter ought to be. Recommendations have been made regarding the use of premedicant drugs and volatile anaesthetic agents to reduce the incidence of awareness.     

Nitrous oxide‐based vs. nitrous oxide‐free general anaesthesia and accidental awareness in surgical patients: an abridged Cochrane systematic review

Accidental awareness during general anaesthesia can arise from a failure to deliver sufficient anaesthetic agent, or from a patient's resistance to an expected sufficient dose of such an agent. Awareness is ‘explicit’ if the patient is subsequently able to recall the event. We conducted a systematic review into the effect of nitrous oxide used as part of a general anaesthetic on the risk of accidental awareness in people over the age of five years undergoing general anaesthesia for surgery. We included 15 randomised controlled trials, 14 of which, representing a total of 3439 participants, were included in our primary analysis of the frequency of accidental awareness events. The awareness incidence rate was rare within these studies, and all were considered underpowered with respect to this outcome. The risk of bias across all studies was judged to be high, and 76% of studies failed adequately to conceal participant allocation. We considered the available evidence to be of very poor quality. There were a total of three accidental awareness events reported in two studies, one of which reported that the awareness was the result of a kink in a propofol intravenous line. There were insufficient data to conduct a meta‐ or sub‐group analysis and there was insufficient evidence to draw outcome‐related conclusions. We can, however, recommend that future studies focus on potentially high‐risk groups such as obstetric or cardiac surgery patients, or those receiving neuromuscular blocking drugs or total intravenous anaesthesia.     

Recall of awareness during cardiac anaesthesia: influence of feedback information to the anaesthesiologist

We interviewed 303 cardiac surgery patients to evaluate the incidence of intraoperative awareness with recall.
First, we randomly interviewed 99 patients, of whom four patients (4%) reported awareness and recall. We informed the cardiac anaesthesiologists of the results of these interviews, and we also gave general information regarding means to reduce awareness and recall during general anaesthesia. Thereafter, we interviewed 204 consecutive cardiac surgery patients. Now, three of the patients (1.5%) had intraoperative awareness with recall. The reduction in the incidence from 4% to 1.5% was not significant. However, the doses of principal anaesthetic drugs had increased significantly between the two interview phases, while the dose of pancuronium, the main muscle relaxant used, had decreased significantly. Also, there was a significant increase in the number of anaesthesias where anaesthetic agents had been administered continuously instead of bolus or non-continuous dosing techniques. Between the patients with awareness and recall and those without it, there was no difference in the doses of anaesthetic agents given. The patients with awareness were significantly younger than those not aware.
In conclusion, with educational measures and vigilance over the problem, the incidence of intraoperative awareness during cardiac anaesthesia may be reduced. The incidence figure of 1.5% we observed is of the magnitude reported recently by others with modern cardiac anaesthesia techniques.     

Wachzustände während Allgemeinanästhesie Definition,Häufigkeit,klinische Relevanz,Ursachen, Vermeidung und medikolegale Aspekte

The possibility that a patient during general anaesthesia is aware of the operation going on and aware of severe pain that might be remembered postoperatively must be very alarming to patients and anaesthetists alike. Furthermore, there is experimental evidence showing that conscious recall of intraoperative events is only the tip of an iceberg; it seems very probable that there is even a higher incidence of unconscious perception during general anaesthesia. Therefore, the following stages of intraoperative awareness must be distinguished: (1) conscious awareness with explicit recall and with severe pain; (2) conscious awareness with explicit recall but no complaints of pain; (3) conscious awareness without explicit recall and possible implicit recall; (4) subconscious awareness without explicit recall and possible implicit recall; (5) no awareness. The incidence of conscious awareness with explicit recall and severe pain has been estimated at less frequent than 1/3000 general anaesthetics. Conscious awareness with explicit recall but no complaints of pain has been reported in the literature with an incidence of 0.5–2%. With 7–72%, conscious awareness without explicit recall and possible implicit recall shows a very wide range of variation and its occurrence probably depends on the anaesthetic drugs used. Subconscious awareness with possible implicit recall has an incidence of up to 80%, but there are many methodological problems in demonstrating implicit memory of intraoperative events. Reports of intraoperative awareness do not come exclusively from cardiac surgery and obstetrics, but also from all other operative specialities. Postoperatively, patients who experienced intraoperative awareness may develop a so-called post-traumatic stress syndrome. Symptoms involve re-experiencing the event awake or in dreams, sleep disturbances, depression, avoidance of stimuli associated with the event. The probability of the development of the post-traumatic stress syndrome seems to coincide with the experience of severe pain. When a patient complains of intraoperative awareness postoperatively the anaesthesiologist should discuss the event frankly with the patient. When the symptoms of the post-traumatic stress syndrome persist a psychotherapy should follow. Causes for intraoperative awareness may be: equipment failure, too-light anaesthesia, e.g. for a caesarean section or for emergency surgery in severely injured or polytraumatized patients, during cardiac surgery, bronchoscopy or difficult intubation. There is interindividual variability in anaesthetic effect; for example, chronic drug or alcohol abuse or overweight may make increased anaesthetic doses necessary. They are at risk for intraoperative awareness. Some general anaesthetics or anaesthetic procedures, e.g. the combination of a relaxant and N₂O, opioid mono-anaesthetics, or opioids combined with benzodiazepines, seem to involve a higher risk of intraoperative awareness than do volatile anaesthetics. The bases of litigation are medical malpractice, breach of contract by the anaesthesiologist or lack of informed consent from the patient. Therefore, patients who are at risk of intraoperative awareness should be given detailed information on this special risk before the operation.     

The 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: protocol,methods and analysis of data

Accidental awareness during general anaesthesia with recall is a potentially distressing complication of general anaesthesia that can lead to psychological harm. The 5th National Audit Project was designed to investigate the reported incidence, predisposing factors, causality and impact of accidental awareness. A nationwide network of local co‐ordinators across all UK and Irish public hospitals reported all new patient reports of accidental awareness to a central database, using a system of monthly anonymised reporting over a calendar year. The database collected the details of the reported event, anaesthetic and surgical technique, and any sequelae. These reports were categorised into main types by a multidisciplinary panel, using a formalised process of analysis. The main categories of accidental awareness were: certain or probable; possible; during sedation; on or from the intensive care unit; could not be determined; unlikely; drug errors; and statement only. The degree of evidence to support the categorisation was also defined for each report. Patient experience and sequelae were categorised using current tools or modifications of such. The 5th National Audit Project methodology may be used to assess new reports of accidental awareness during general anaesthesia in a standardised manner, especially for the development of an ongoing database of case reporting. This paper is a shortened version describing the protocols, methods and data analysis from 5th National Audit Project – the full report can be found at http://www.nationalauditprojects.org.uk/NAP5_home#pt .     

Monitoring intraoperativer Wachzustände Vegetative Zeichen,isolierte Unterarmtechnik,Elektroenzephalogramm und akustisch evozierte Potentiale

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 midlatency 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 imployed. 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.     

Arterial hypertension associated with the use of a tourniquet with either general or regional anaesthesia

A hypertensive patient with left cardiac enlargement developed marked hypertension under general anaesthesia, during which time a tourniquet was applied around his thigh. When the tourniquet was released, severe hypotension ensued which responded to therapy. The patient, however, died 16 h later of a myocardial infarction. Because of this incident, the anaesthetic and haemodynamic data of 699 patients who underwent limb surgery with a pneumatic tourniquet inflated for at least an hour were retrospectively examined using multivariate analysis. A 30% increase in systolic and/or diastolic arterial blood pressure occurred in 27% of the total patient material and in 67% of those who had had a general anaesthetic. There was a higher frequency of the occurrence of "tourniquet hypertension" with older age, longer operations and the operation site being the lower rather than the upper limb. Tourniquet hypertension rarely occurred in patients with spinal anaesthesia (2.7%) and brachial plexus blockade (2.5%), while those with intravenous regional anesthesia had a higher incidence (19%) of hypertension.     

Bispectral index in assessment of adequacy of general anaesthesia for lower segment caesarean section

Awareness among parturients during general anaesthesia for caesarean section, though now uncommon, remains a concern for obstetric anaesthetists. We examined the adequacy of our general anaesthetic technique for avoiding explicit awareness by determining the depth of anaesthesia using Bispectral Index (BIS) monitoring. Twenty ASA1 parturients having general anaesthesia for lower segment caesarean section were studied. The drugs and doses used for each anaesthetic were similar Intraoperative Bispectral Index, haemodynamic parameters, end-tidal isoflurane concentration and inspired nitrous oxide fraction were measured and the postoperative incidence of explicit awareness was assessed. All anaesthetists were blinded to the Bispectral Index value throughout the operation. The depth of anaesthesia at various stages of the operation was evaluated by recording the Bispectral Index. Patients were interviewed for any intraoperative recall or awareness at the end of operation. A median BIS of 70 or below was recorded on most occasions during surgery. The range was 52 to 70, with values reaching 60 and below at intubation, uterine incision and delivery. Haemodynamic stability was satisfactory and there was no case of uterine atony, fetal compromise or postpartum haemorrhage. No patient experienced intraoperative dreams, recall or awareness. Our current general anaesthetic technique appeared inadequate to reliably produce BIS values of less than 60 that are associated with a low risk of awareness. However, no patients experienced explicit awareness.     

The claims of compensation for awareness with recall during general anaesthesia in Finland

Background: Awareness during anaesthesia has been estimated to occur in 0.2%-0.4% of patients undergoing general surgery. In Finland, according to the Patient Injury Act, compensation is paid for an injury caused by medical treatment. We have analysed the claims for compensation involving awareness under anaesthesia filed between May, 1987 and December, 1993.
Methods: Original claims, hospital notes, and expert advisor's comments as well as the comments of the anaesthesiologist in charge of the anaesthesia, and decisions of the Patient Injury Association, were reviewed.
Results: A total of 23 363 claims of patient injury were made during the study period. Of these, 391 considered anaesthetic treatments, and there were four cases of awareness with recall.
Conclusion: Claims of compensation for awareness during anaesthesia were surprisingly few, possible reasons of which are discussed. Compensations paid were low in comparison with some other countries.     

A myoclonic seizure during propofol-alfentanil anesthesia?]

Total intravenous anaesthesia with propofol and alfentanil is an established alternative to inhalation anaesthesia for intracranial neurosurgical procedures. Its usefulness has been somewhat overshadowed by reports of seizure-like movements, both during anaesthesia and in the recovery period. These can be related to the use of either anaesthetic agent, but true epileptogenic properties still remain to be demonstrated in man. Opioid-induced rigidity is a well known phenomenon and must not be mistaken for an epileptic seizure. Myoclonic motor activity can be observed even under physiological conditions, e.g. sleep. Almost all anaesthetic agents have been found to produce "epileptic" EEG changes (spikes, polyspikes, spike-wave complexes), but in man these have never been correlated to motor reactions. Propofol's pro- or anticonvulsive action is unclear. While some groups found shortened convulsing times in patients undergoing electroconvulsive therapy with propofol instead of methohexitone, others have reported activation of epileptogenic foci in the EEGs of known epileptic patients. A synergistic effect of propofol and alfentanil in the generation of seizure-like movements cannot be excluded. Whether seizure-like movements indicate a true "epileptogenic potency" of the anaesthetic drugs or are related to other phenomena remains to be studied. Electro-encephalographic monitoring during anaesthesia as well as careful observation and documentation of motor reactions may contribute to elucidation of the problem. We report a case of seizure-like movements during propofol-alfentanil anaesthesia for an elective craniotomy. A 52-year-old patient presented with a history of headaches of increasing frequency. A CT brain scan demonstrated a tumor in the left occipital region.(ABSTRACT TRUNCATED AT 250 WORDS)     

Messung der Narkosetiefe, Awareness und EEG

Inapparent adverse intraoperative wakefulness is still a relevant problem in modern anaesthetic routine. It can be associated with serious negative effects on the postoperative recovery of the patients. Several different procedures have been developed to monitor and therefore avoid intraoperative situations of wakefulness during general anaesthesia. The most promising methods are the PRST-score, calculated from changes in the blood pressure, heart rate, sweating and tear production, the so-called isolated forearm technique, spontaneous EEG and its derived parameters such as spectral edge frequencies or BIS and finally mid-latency auditory evoked potentials. The observation of clinical autonomic signs, even including the calculation of the PRST-score does not seem to be valid enough to indicate or predict intraoperative wakefulness. The isolated forearm technique can be regarded as the most reliable tool to detect intraoperative wakefulness, but it can only be applied for a very limited period of time. The processed EEG with the median frequency, spectral edge frequency or bispectral index are important scientific tools to quantify central anaesthetic effects especially to develop pharmacodynamic-pharmacokinetic models of anaesthetic action. But they seem to be less suitable to indicate situations of intraoperative wakefulness or awareness. The mid-latency auditory evoked potentials are depressed dose-dependently by a series of anaesthetic agents, which correlate with the occurrence of situations of intraoperative wakefulness and awareness. There is a hierarchical correlation between certain values of the MLAEP and intraoperative wakefulness defined by purposeful movements, amnesic awareness with only implicit recall and conscious awareness with explicit recall. For some of the most commonly used anaesthetics reasonable threshold values of the MLAEP for the different states of consciousness have already been determined. Future studies in broad patient populations with all of the different routinely used anesthetics and procedures will have to finally identify the importance of the recording of mid-latency auditory evoked potentials as a routine method to assess the depth of anaesthesia.     

Intravenous glucose tolerance test during anaesthesia in dogs: insulin response and glucose clearance

To evaluate the insulin response and the rates of disappearance of glucose from plasma during high spinal analgesia and various types of general anaesthesia, a series of intravenous glucose tolerance tests was performed in six dogs. Plasma glucose and insulin levels were measured during the intravenous glucose tolerance tests. Insulinogenic indices were calculated. The values obtained during anaesthesia were compared to those obtained during an unanaesthetized state. The insulinogenic index was increased significantly during high spinal analgesia and thiopentone infusion. Halothane and enflurane anaesthesia decreased the insulinogenic index significantly while Innovar-nitrous oxide also decreased it, but not significantly. These findings suggest that insulin secretion in response to hyperglycaemia is stimulated by spinal analgesia and thiopentone anaesthesia, depressed by halothane and enflurane anaesthesia and unchanged during neuroleptanesthesia. A diuresis was observed in the thiopentone anaesthetic and spinal analgesic groups as compared to the other general anaesthetic groups. Urinary losses of insulin and glucose paralleled urinary output; yet the greatest mean urinary loss of glucose did not exceed 4.5 per cent of the load of glucose administered. Accordingly, 95 per cent of the administered glucose remained within the body, presumably available for utilization.     

Accidental awareness during general anaesthesia – a narrative review

Unintended accidental awareness during general anaesthesia represents failure of successful anaesthesia, and so has been the subject of numerous studies during the past decades. As return to consciousness is both difficult to describe and identify, the reported incidence rates vary widely. Similarly, a wide range of techniques have been employed to identify cases of accidental awareness. Studies which have used the isolated forearm technique to identify responsiveness to command during intended anaesthesia have shown remarkably high incidences of awareness. For example, the ConsCIOUS‐1 study showed an incidence of responsiveness around the time of laryngoscopy of 1:25. On the other hand, the 5th Royal College of Anaesthetists National Audit Project, which reported the largest ever cohort of patients who had experienced accidental awareness, used a system to identify patients who spontaneously self‐reported accidental awareness. In this latter study, the incidence of accidental awareness was 1:19,600. In the recently published SNAP‐1 observational study, in which structured postoperative interviews were performed, the incidence was 1:800. In almost all reported cases of intra‐operative responsiveness, there was no subsequent explicit recall of intra‐operative events. To date, there is no evidence that this occurrence has any psychological consequences. Among patients who experience accidental awareness and can later remember details of their experience, the consequences are better known. In particular, when awareness occurs in a patient who has been given neuromuscular blocking agents, it may result in serious sequelae such as symptoms of post‐traumatic stress disorder and a permanent aversion to surgery and anaesthesia, and is feared by patients and anaesthetists. In this article, the published literature on the incidence, consequences and management of accidental awareness under general anaesthesia with subsequent recall will be reviewed.     

Awareness during general anaesthesia: a review of 81 cases from the Anaesthetic Incident Monitoring Study

Because of recent studies suggesting that awareness is still a major issue in anaesthetic practice, we reviewed 8372 incidents reported to the Anaesthetic Incident Monitoring Study. There were 81 cases in which peri-operative recall was consistent with awareness. There were 50 cases of definite awareness and 31 cases with a high probability of awareness. In 13 of the 81 incidents, the patients appeared to receive adequate doses of anaesthetic drugs. Where the cause could be determined, awareness was mainly due to drug error resulting in inadvertent paralysis of an awake patient (n = 32) and failure of delivery of volatile anaesthetic (n = 16). Less common causes included prolonged attempts at intubation of the trachea (n = 5), deliberate withdrawal of volatile anaesthetic (n = 4) or muscle relaxant apnoea with inadequate administration of hypnotic (n = 3). An objective central nervous system depth of anaesthesia monitor may have prevented 42 of these incidents and an improved drug administration system may have prevented 32. On the basis of these reports, we have developed guidelines that may have prevented the majority of these incidents.     

The 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: summary of main findings and risk factors

We present the main findings of the 5th National Audit Project on accidental awareness during general anaesthesia. Incidences were estimated using reports of accidental awareness as the numerator, and a parallel national anaesthetic activity survey to provide denominator data. The incidence of certain/probable and possible accidental awareness cases was ~1:19 600 anaesthetics (95% CI 1:16 700–23 450). However, there was considerable variation across subtypes of techniques or subspecialties. The incidence with neuromuscular blockade was ~1:8200 (1:7030–9700), and without it was ~1:135 900 (1:78 600–299 000). The cases of accidental awareness during general anaesthesia reported to 5th National Audit Project were overwhelmingly cases of unintended awareness during neuromuscular blockade. The incidence of accidental awareness during caesarean section was ~1:670 (1:380–1300). Two thirds (82, 66%) of cases of accidental awareness experiences arose in the dynamic phases of anaesthesia, namely induction of and emergence from anaesthesia. During induction of anaesthesia, contributory factors included: use of thiopental; rapid sequence induction; obesity; difficult airway management; neuromuscular blockade; and interruptions of anaesthetic delivery during movement from anaesthetic room to theatre. During emergence from anaesthesia, residual paralysis was perceived by patients as accidental awareness, and commonly related to a failure to ensure full return of motor capacity. One third (43, 33%) of accidental awareness events arose during the maintenance phase of anaesthesia, most due to problems at induction or towards the end of anaesthesia. Factors increasing the risk of accidental awareness included: female sex; age (younger adults, but not children); obesity; anaesthetist seniority (junior trainees); previous awareness; out‐of‐hours operating; emergencies; type of surgery (obstetric, cardiac, thoracic); and use of neuromuscular blockade. The following factors were not risk factors for accidental awareness: ASA physical status; race; and use or omission of nitrous oxide. We recommend that an anaesthetic checklist, to be an integral part of the World Health Organization Safer Surgery checklist, is introduced as an aid to preventing accidental awareness. This paper is a shortened version describing the main findings from 5th National Audit Project – the full report can be found at http://www.nationalauditprojects.org.uk/NAP5_home#pt .     

MIDAZOLAM-ALFENTANIL: AN ANAESTHETIC? AN INVESTIGATION USING THE ISOLATED FOREARM TECHNIQUE

Thirty-two women underwent major gynaecological surgery witha midazolam-alfentanil total i.v. anaesthetic regimen. Adequacyof anaesthesia was assessed using a "pressure, rate, sweatingand tears" (PRST) scoring system in conjunction with the isolatedforearm technique (IFT). The IFT revealed that 72% of patientsresponded during surgery, but none had spontaneous, unpromptedpostoperative recall for the event. Three patients, on prompting,provided evidence of recall. The IFT, while indicating whichpatients are responsive, cannot be used to predict who willhave postoperative recall. Lack of explicit postoperative recalldoes not indicate unconsciousness during surgery. Twenty patients,asked specifically during surgery to indicate the presence orabsence of pain, experienced pain at some time during theirsurgical procedure. The PRST score could not be used to predictwhen a patient was awake. This low-dose i. v. anaesthetic techniquecannot be recommended for general use. (Br. J. Anaesth. 1993;70: 42–46)     

Maintenance of anaesthesia

Key goals for the maintenance phase of general anaesthesia are the provision of surgical anaesthesia while maintaining physiological parameters at levels that preserve organ function and avoid injury. Maintenance can be achieved with either inhaled or intravenous anaesthetic agents. A good understanding of the physiochemical properties of these agents is necessary for effective manipulation of depth of anaesthesia at any stage. Drugs suitable for total intravenous anaesthesia are mainly those with short context-sensitive half-times, such as propofol, remifentanil, and dexmedetomidine. Target-controlled infusion pumps utilize three compartment models in complex calculations to achieve the desired effect-site concentration. Monitoring during anaesthesia has been proven to reduce risk in the perioperative period. Sustained vigilance and good exchange of information at handover between anaesthetists are other essential aspects of safe anaesthesia during the maintenance phase.     

Peroperative Haemorrhage and Epidural Anaesthesia in Major Abdominal Surgery A Retrospective Study

The peroperative blood loss during resection of the colon, abdominal-perineal excision of the rectum and cystectomy, according to the method of Bricker, was studied from anaesthetic reports. The period under study was 18 months.
A total of 97 patients were divided into two main groups according to the type of anaesthesia (general anaesthesia and general anaesthesia combined with epidural analgesia), as well as into sub-groups according to the type of operation.
An evaluation was made of the blood loss, peroperative mean arterial blood pressure and the duration of the operation.
In contrast to reports published earlier on other types of operation, we have been unable to demonstrate a significant reduction in the blood loss of patients given general anaesthesia plus epidural analgesia, despite a lower mean arterial blood pressure during the operation.
We ignored any possible postoperative beneficial effect of epidural anaesthesia.     

Awareness in retrieval medicine

Awareness is the spontaneous recall of an event(s) that occurred during general anaesthesia and surgery. The incidence of awareness is approximately 0.2% of cases where neuromuscular blockers are used and half that where they are omitted. The majority of data relating to awareness is from anaesthetic practice. We report a case of awareness associated with an out-of-hospital transportation of a critically ill patient requiring a medical escort (retrieval). We discuss the risk factors associated with awareness during retrieval, in particular the trend toward excessive administration of neuromuscular blockers, and the unique challenges for the prevention of awareness within the retrieval environment.     

Attitudes of anaesthetists to awareness and depth of anaesthesia monitoring in the UK

BACKGROUND AND OBJECTIVE: Awareness with postoperative recall of intraoperative events is a rare but serious complication of general anaesthesia. This survey investigated the attitude of anaesthetists in the UK to awareness and depth of anaesthesia monitoring. METHODS: Questionnaires were sent to 4927 consultant anaesthetists in 285 hospitals in the UK in September 2004. The responses were recorded in an electronic database, summarized and compared with the results of studies performed in Australia and the USA. RESULTS: The response rate was 44%. When judged against published awareness rates, anaesthetists underestimated the incidence of awareness in their own practice (median 1: 5000). One-third of respondents have dealt with patients who have experienced intraoperative recall. The majority of anaesthetists perceived awareness as a minor problem on an 11-point scale (modal score 2, median score 3, IQR 2-5). Eighty-six percent of anaesthetists considered clinical signs unreliable but 91% felt that measurement of end-tidal anaesthetic agent concentration reduces the likelihood of awareness. The majority of anaesthetists would use a monitor at least some of the time if one was available to them. Overall, the attitudes of anaesthetists in the UK, USA and Australia are remarkably similar. CONCLUSIONS: Anaesthetists tend not to view awareness as a serious problem. Although most accept that clinical signs are unreliable indicators of awareness, few believe that monitors of anaesthetic depth should be used for routine cases.