Awareness under anesthesia, also referred to as intraoperative awareness or accidental awareness during general anesthesia (AAGA), is a rare complication of general anesthesia wherein patients regain varying levels of consciousness during their surgical procedures. While anesthesia awareness is possible without resulting in any long-term memory of the experience, it is also possible for victims to have awareness with explicit recall, where they can remember the events related to their surgery (intraoperative awareness with explicit recall).

Intraoperative awareness with explicit recall is an infrequent condition with potentially devastating psychological consequences. While it has gained popular recognition in the press, research shows that it occurs at an incidence rate of only 0.1–0.2%. Patients report a variety of experiences, ranging from vague, dreamlike states to being fully awake, immobilized, and in pain from the surgery. Intraoperative awareness is usually caused by the delivery of inadequate anesthetics relative to the patient's requirements. Risk factors can be anesthetic (e.g., use of neuromuscular blockade drugs, use of intravenous anesthetics, technical/mechanical errors), surgical (e.g., cardiac surgery, trauma/emergency, C-sections), or patient-related (e.g., reduced cardiovascular reserve, history of substance use, history of awareness under anesthesia).

Currently, the mechanism behind consciousness and memory under anesthesia is unknown, although there are many working hypotheses. However, intraoperative monitoring of anesthetic level with bispectral index (BIS) or end-tidal anesthetic concentration (ETAC) may help to reduce the incidence of intraoperative awareness, although clinical trials have yet to show a decreased incidence of AAGA with the BIS monitor.

There are also many preventative techniques considered for high-risk patients, such as pre-medicating with benzodiazepines, avoiding complete muscle paralysis, and managing patients' expectations. Diagnosis is made postoperatively by asking patients about potential awareness episodes and can be aided by the modified Brice interview questionnaire. A common but devastating complication of intraoperative awareness with recall is the development of post-traumatic stress disorder (PTSD) from the events experienced during surgery. Prompt diagnosis and referral to counseling and psychiatric treatment are crucial to the treatment of intraoperative awareness and the prevention of PTSD.

Signs and symptoms Intraoperative awareness can present with a variety of signs and symptoms. A large proportion of patients report vague, dreamlike experiences, while others report specific intraoperative events, such as: hearing noises or conversations in the operating room remembering details of the operation sensing pain associated with intubation or surgery having weakness or muscle paralysis feeling anxiety, helplessness, or an impending sense of doom

Intraoperative signs that may indicate patient awareness include: hypertension tachycardia patient movement tachypnea intravenous anesthesia line infiltrated or occluded

Patients under anesthesia are paralyzed if a neuromuscular blockade drug, a type of muscle relaxant, has been given as part of general anesthesia. When paralyzed, patients may not be able to communicate their distress or alert the operating room staff of their consciousness until the paralytic wears off. After surgery, recognition of the symptoms of an awareness event may be delayed. One review showed that only about 35% of patients are able to report an awareness event immediately after the surgery, with the rest remembering the experience from weeks to months afterward. Depending on the awareness experience, patients may have postoperative psychological problems that range from mild anxiety to post-traumatic stress disorder (PTSD). PTSD is characterized by recurrent anxiety, irritability, flashbacks or nightmares, avoidance of triggers related to the trauma, and sleep disturbances.

Causes

Paralytic and muscle relaxant use

The biggest risk factor is anesthesia performed by unsupervised trainees and the use of a medication that induces muscle paralysis, such as suxamethonium (succinylcholine) or non-depolarizing neuromuscular blocking drugs (muscle relaxants). During general anesthesia, the patient's muscles may be paralyzed in order to facilitate tracheal intubation or surgical exposure (abdominal and thoracic surgery can be performed only with adequate muscle relaxation). Because the patient cannot breathe for themselves, mechanical ventilation must be used. The paralyzing agent does not cause unconsciousness or take away the patient's ability to feel pain, but does prevent the patient from breathing, so the airway (trachea) must be protected and the lungs ventilated to ensure adequate oxygenation of the blood and removal of carbon dioxide.

A fully paralyzed patient is unable to move, speak, blink the eyes, or otherwise respond to the pain. If neuromuscular blocking drugs are used, this causes skeletal muscle paralysis but does not interfere with cardiac or smooth muscle or the functioning of the autonomic nervous system, so heart rate, blood pressure, intestinal peristalsis, sweating and lacrimation are unaffected. The patient cannot signal distress and may not exhibit the signs of awareness that would be expected to be detectable by clinical vigilance, because other drugs used during anaesthesia may block or obtund these.

Many types of surgery do not require the patient to be paralyzed. A patient who is anesthetized but not paralyzed can move in response to a painful stimulus if the analgesia is inadequate. This may serve as a warning sign that the anesthetic depth is inadequate. Movement under general anesthesia does not imply full awareness but is a sign that the anesthesia is light. Even without the use of neuromuscular blocking drugs the absence of movement does not necessarily imply anesthesia.

Light anesthesia

For certain operations, such as caesarean section, or in hypovolemic patients or patients with minimal cardiac reserve, the anesthesia provider may aim to provide "light anesthesia" and should discuss this with patients to warn them. During such circumstances, consciousness and recall may occur because judgments of depth of anesthesia are not precise. The anesthesia provider must weigh the need to keep the patient safe and stable with the goal of preventing awareness. Sometimes, it is necessary to provide lighter anesthesia in order to preserve the life of the patient. "Light" anesthesia means less drugs by the intravenous route or via inhalational means, leading to less cardiovascular depression (hypotension) but permitting "awareness" in the anesthetized subject.

Human error

Human errors include repeated attempts at intubation during which the short-acting anesthetic may wear off but the paralyzing drug does not; esophageal intubation; inadequate drug dose; a drug given by the wrong route or a wrong drug given; drugs given in the wrong sequence; inadequate monitoring; patient abandonment; disconnections and kinks in tubes from the ventilator; and failure to refill the anesthetic machine's vaporizers with volatile anesthetic. Other causes include unfamiliarity with techniques used, e.g. ⁠intravenous anesthetic regimes, and inexperience. Most cases of awareness are caused by inexperience and poor anesthetic technique, which can be any of the above, but also includes techniques that could be described as outside the boundaries of "normal" practice. The American Society of Anesthesiologists in 2007 released a Practice Advisory outlining the steps that anesthesia professionals and hospitals should take to minimize these risks. Other societies have released their own versions of these guidelines, including the Australian and New Zealand College of Anaesthetists.

To reduce the likelihood of awareness, anesthetists must be adequately trained, and supervised while still in training. Equipment that monitors depth of anesthesia, such as bispectral index monitoring, should not be used in isolation.

Current research attributes the incidence of AAGA to a combination of the risks mentioned above, together with ineffective practice from ODPs, anesthetic nurses, HCAs and anesthetists. The main failures include: Inattention or judgment errors related to drugs and volatile agents Termination of anesthesia too soon before surgery has finished, due to poor communication Lack of understanding of offset times of volatile agents Backflow of induction agent up a giving set Failure to fill vaporizers (which is the cause of 19% of the cases of AAGA) Under-dosing of induction agent during difficult intubation Failure to monitor MAC (minimum alveolar concentration of inhaled anaesthetic required to prevent movement in 50% of patients in response to surgical incision) Syringe swaps Rushing caused by organizational or individual circumstances (often associated with staff shortage and stressful work environment) Distractions caused by another member of staff

Equipment failure

Machine malfunction or misuse may result in an inadequate delivery of anesthetic. Many Boyle's machines in hospitals have the oxygen regulator serving as a slave to the pressure in the nitrous oxide regulator, to enable the nitrous oxide cut-off safety feature. If nitrous oxide delivery suffers due to a leak in its regulator or tubing, an 'inadequate' mixture can be delivered to the patient, causing awareness. Many World War II-vintage Boyle 'F' models are still functional and used in UK hospitals. Their emergency oxygen flush valves have a tendency to release oxygen into the breathing system, which, when added to the mixture set by the anesthesiologist, can lead to awareness. This may also be caused by an empty vaporizer (or nitrous oxide cylinder) or a malfunctioning intravenous pump or disconnection of its delivery tubing. Patient abandonment (when the anesthesiologist is no longer present) causes some cases of awareness and death.

Patient physiology Very rare causes of awareness include drug tolerance, or a tolerance induced by the interaction of other drugs. Some patients may be more resistant to the effects of anesthetics than others; factors such as younger age, obesity, tobacco smoking, or long-term use of certain drugs (alcohol, opioids, or amphetamines) may increase the anesthetic dose needed to produce unconsciousness. There may be genetic variations that cause differences in how quickly patients clear anesthetics, and there may be differences in how the sexes react to anesthetics as well. In addition, anesthetic requirement is increased in persons with naturally red hair. Marked anxiety prior to the surgery can increase the amount of anesthesia required to prevent recall.

Conscious sedation

There are various levels of consciousness. Full wakefulness and general anesthesia are the two extremes of the spectrum. Conscious sedation and monitored anesthesia care (MAC) refer to an awareness somewhere in the middle of the spectrum, depending on the degree to which a patient is sedated. Monitored anesthesia care involves titration of local anesthesia along with sedation and analgesia. Awareness/wakefulness does not necessarily imply pain or discomfort. The aim of conscious sedation or MAC is to provide a safe and comfortable anesthetic while maintaining the patient's ability to follow commands.