Accidental awareness is one of the most feared complications of general anaesthesia for both patients and anaesthetists. Patients report this failure of general anaesthesia in approximately 1 in every 19,000 cases, according to a new report published in the journal Anaesthesia.
Known as accidental awareness during general anaesthesia (AAGA), the terrifying complication occurs when general anaesthesia is intended but the patient remains conscious.
The updated estimate of patient reports of accidental awareness is much lower than previous figures, which were as high as 1 in 600. But the investigation also uncovered startling new findings about the long-term psychological consequences for those who experience accidental awareness.
The findings come from the largest-ever study of accidental awareness, the 5th National Audit Project (NAP5), which has been conducted over the last three years by the Royal College of Anaesthetists (RCoA) and the Association of Anaesthetists of Great Britain and Ireland (AAGBI).
“The project dramatically increases our understanding of anaesthetic awareness and highlights the range and complexity of patient experiences. NAP5, as the biggest ever study of this complication, has been able to define the nature of the problem and those factors that contribute to it more clearly than ever before,” says Dr. Tim Cook, Consultant Anaesthetist in Bath and co-author of the report. “As well as adding to the understanding of the condition, we have also recommended changes in practice to minimize the incidence of awareness and, when it occurs, to ensure that it is recognized and managed in such a way as to mitigate longer-term effects on patients.”
The use of general anaesthesia is normally safe and produces a state of sedation that doesn’t break in the middle of a procedure, doctors say. The patient and anaesthesiologist collect as much medical history as possible beforehand, including alcohol and drug habits, to help determine the most appropriate anesthetic.
While many of us think of it as “going to sleep,” in terms of what your body is doing, general anaesthesia has very little in common with taking a nap. During sleep, the brain is in its most active state; anaesthesia, on the other hand, depresses central nervous system activity. On the operating table, your brain is less active and consumes less oxygen — a state of unconsciousness nothing like normal sleep.
Doctors do not know exactly how general anesthesia produces this effect. It is clear that anesthetic drugs interfere with the transmission of chemicals in the brain across the membranes, or walls, of cells. But the mechanism remains the subject of ongoing research, and for many of us, the subject of our worst nightmares.
40 percent of AAGA cases led to long-term psychological harm
In the new study, researchers analyzed patient data from surgical and medical interventions in which anaesthesia care was provided, covering every public hospital in the UK and Ireland. During the study period from June 2012 through May 2013, more than 300 new reports of accidental awareness were reported.
The extensive analysis showed that the majority of episodes of awareness are short-lived, occur before surgery starts or after it finishes, and do not always cause concern to patients.
However, 51 percent of episodes led to distress and 41 percent to longer-term psychological harm, the team found. Sensations commonly experienced during these episodes included tugging, stitching, pain, paralysis, and choking; patients described feelings of dissociation, panic, extreme fear, suffocation, and even dying.
Most patients who reported feeling distressed at the time of the incident ended up suffering from chronic psychological distress, and many developed full-blown psychiatric conditions — namely, post-traumatic stress disorder.
One patient, Sandra, described her feelings when, as a 12-year-old, she suffered an episode of AAGA during a routine orthodontic operation:
“Suddenly, I knew something had gone wrong,” said Sandra, “I could hear voices around me, and I realized with horror that I had woken up in the middle of the operation, but couldn’t move a muscle… while they fiddled, I frantically tried to decide whether I was about to die.”
For many years after the operation Sandra described experiencing nightmares in which, “a Dr. Who style monster leapt on me and paralyzed me.” Sandra experienced the nightmares for more than 15 years until she realized the link: “I suddenly made the connection with feeling paralyzed during the operation; after that I was freed of the nightmare and finally liberated from the more stressful aspects of the event.”
Sandra’s account is borne out by the research findings that longer-term adverse effects are closely linked with patients experiencing a sensation of paralysis during their awareness. The use of drugs (muscle relaxants) to temporarily stop muscles from working, often needed for safe surgery, is responsible for the experience. Distress during paralysis appears to be key in the development of later psychological symptom, the researchers found.
“It is clear that the sensation of paralysis is a novel one with capacity to cause great psychological harm, unless it is counteracted by general anaesthesia,” the authors wrote. Conversely, AAGA without paralysis is far less likely to result in psychological distress.
AAGA risk factors
The team, led by Dr. Jaideep Pandit, Consultant Anaesthetist in Oxford, identified a variety of risk factors associated with the incidence of accidental awareness, including those related to surgery and drug type, patient characteristics, and organizational variables.
For instance, the vast majority of cases of accidental awareness took place during surgeries in which a neuromuscular blockade was used to induce temporary paralysis, and two thirds of the incidents arose during the dynamic phases of anaesthesia, which encompasses induction of and emergence from anaesthesia. Use of the drug thiopental was also associated with an increased incidence of AAGA.
Furthermore, the team found that AAGA is significantly more common during caesarean sections (associated with a 10-fold increase in AAGA) and cardiothoracic surgery (associated with a 2.5-fold increase in AAGA) compared to other procedures. The risk is also higher for obese patients, and during surgeries when there is difficulty managing the airway at the start of anaesthesia.
Other factors found to increase the risk of accidental awareness included: female sex; age (younger adults, but not children); anaesthetist seniority (junior trainees); previous accidental awareness; interruptions of anaesthetic delivery during movement from anaesthetic room to surgical theater; out-of-hours operating; and emergencies.
“However,” says Dr. Pandit, “the most compelling risk factor is the use of muscle relaxants, which prevent the patient [from] moving.”
Preventing accidental awareness
Meticulous monitoring of anaesthesia depth and patient response is critically important for the prevention of AAGA. According to the American Society of Anesthesiologists, anesthesiologists are required to monitor patients during the entire course of their surgery. During this time, they’re supposed to make sure patients are getting proper amounts of anaesthetic drugs; that they’re breathing properly, with the help of oxygen and mechanical ventilators; that their blood — and the drugs — is circulating properly, and that body temperature is constant.
However, while these are critical steps that greatly enhance the safety of surgical procedures involving anaesthesia, they are not foolproof. Some organizations, like the Anesthesia Awareness Campaign, are pushing for additional safeguards, including making brain activity monitoring a standard of care.
There has been controversy about the use of brain function monitors in general anesthesia. Advocates say brain monitoring is essential for ensuring the patient achieves the appropriate sedation so as to not wake up. The monitors use a scale of 0 to 100 to reflect what’s going on in the brain: 0 is a total absence of brain activity, 98 to 100 is wide awake, and 45 to 60 is about where general anesthesia puts the patient.
But a 2008 study in the New England Journal of Medicine found no benefit in using brain function monitoring to prevent anesthesia awareness. The American Society of Anesthesiology has said the monitoring is not routinely indicated for general anesthesia, but may have some value and be appropriate for specific patients. The downsides are that they are expensive, and should not be used in place of heart rate and breathing signals when regulating the anesthesia.
Significantly, the team behind the new study reports that “although brain monitors designed to reduce the risk of awareness have a role with certain types of anaesthetic, the study provides little support for their widespread use.”
The researchers note several key limitations — namely, that the data likely underestimate the true prevalence of AAGA. They suggest two competing theories that may explain why AAGA incidents often go unreported. One theory is that the trauma of such experiences is so severe that patients may resist reporting them to avoid re-living the trauma. On the other hand, the researchers say it also possible that some patients never report their experiences with AAGA because they were too trivial to cause concern.
In an accompanying editorial, Drs. Michael Avidan and Jamie Sleigh say the new findings are encouraging, but they warn against becoming complacent with current standards of care:
Taking the NAP5 results in the context of other recent studies, we agree that it is appropriate to convey the message that modern anaesthetic techniques usually succeed in preventing AAGA.
However, it would be regrettable if, based predominantly on NAP5, the public and the medical community were falsely reassured about a vanishingly low incidence of AAGA.
Based on the findings, the project report includes clear recommendations for changes in clinical practice. Two main recommendations are the of a simple anaesthesia checklist to be performed at the start of every operation, and the introduction of an Awareness Support Pathway — a structured approach to the management of patients reporting awareness. These two interventions are designed to decrease errors causing awareness and to minimize the psychological consequences when it occurs.
It is anticipated that NAP5 will lead to changes in the practice of individual anaesthetists, their training, and hospital support systems both nationally and internationally.