Anesthesia awareness

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Awareness under anesthesia, also referred to as intraoperative awareness or accidental awareness during general anesthesia (AAGA), is a rare complication of general anesthesia where 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). [1]

Contents

Intraoperative awareness with explicit recall is an infrequent condition with potentially devastating psychological consequences. [2] While it has gained popular recognition in media, research shows that it only occurs at an incidence rate of 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. [3]

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: [4] [5] [6]

Intraoperative signs that may indicate patient awareness include: [6]

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. [8] 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 weeks to months afterward. [9] Depending on the awareness experience, patients may have postoperative psychological problems that range from mild anxiety to post-traumatic stress disorder (PTSD). [4] [10] PTSD is characterized by recurrent anxiety, irritability, flashbacks or nightmares, avoidance of triggers related to the trauma, and sleep disturbances. [11]

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 amnesia.

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. [12]

Anesthesiologist 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. [13]

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. [2] The main failures include:

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, opiates, 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. [14] 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. [15] 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.

Under certain circumstances, a general anesthetic, whereby the patient is completely unconscious, may be unnecessary or undesirable. For instance, with a caesarean delivery, the goal is to provide comfort with neuraxial anesthetic yet maintain consciousness [16] so that the mother can participate in the birth of the child. Other circumstances may include, but are not limited to, procedures that are minimally invasive or purely diagnostic (and thus not uncomfortable). Sometimes, the patient's health may not tolerate the stress of general anesthesia. The decision to provide MAC versus general anesthesia can be complex, involving careful consideration of individual circumstances and discussion with the patient about their preferences.

Patients who undergo conscious sedation or monitored anesthesia care are never meant to be without recall. [17] Whether a patient remembers the procedure depends on the type of anesthetic, dosages, patient physiology, and other factors. Many patients undergoing monitored anesthesia may go through profound amnesia, depending on the amount of anesthetic used. [18]

Some patients undergo sedation for smaller procedures such as biopsies and colonoscopies and are told they will be asleep, although in fact they are getting a sedation that may allow some level of awareness as opposed to a general anesthetic.

Memory

New research has been carried out to test what people can remember after a general anesthetic, in an effort to understand anesthesia awareness more clearly and help to protect patients from experiencing it. A memory is not one simple entity; it is a system of many intricate details and networks.

Memory is currently classified under two main subsections.

Some researchers are now formally interviewing patients postoperatively to calculate the incidence of anesthesia awareness. It is good practice for the anesthesiologist to visit the patient after the operation and check that the patient was not aware. Most patients who were not unduly disturbed by their experiences do not necessarily report cases of awareness unless directly asked. Many who are greatly disturbed report their awareness but anesthesiologists and hospitals deny that it has happened. It has been found that some patients may not recall experiencing awareness until one to two weeks after undergoing surgery. It was also found that some patients require a more detailed interview to jog their memories for intraoperative experiences but these are only untraumatic cases. Some researchers have found that while anesthesia awareness does not commonly occur in minor surgeries, it may occur more frequently in more serious surgeries, and that it is good practice to warn of the possibility of awareness in those cases where it may be more likely.

Prevention

The risk of awareness is reduced by avoidance of paralytics unless necessary; careful checking of drugs, doses and equipment; good monitoring, and careful vigilance during the case. The Isolated Forearm Technique (IFT) can be used to monitor consciousness; the technique involves applying a tourniquet to the patient's upper arm before the administration of muscle relaxants, so that the forearm can still be moved consciously. [21] [22] The technique is considered a reference standard by which other means of monitoring consciousness can be assessed. [23] [24]

Because the medical staff may not know if a person is unconscious or not, it has been suggested that the staff maintain the professional conduct that would be appropriate for a conscious patient. [25]

Monitors

Recent advances have led to the manufacture of monitors of awareness. Typically these monitor the EEG, which represents the electrical activity of the cerebral cortex, which is active when awake but quiescent under anesthesia (or in natural sleep). The monitors usually process the EEG signal down to a single number, where 100 corresponds to a patient who is fully alert, and zero corresponds to electrical silence. General anesthesia is usually signified by a number between 60 and 40 (this varies with the specific system used). There are several monitors now commercially available. These newer technologies include the bispectral index (BIS), [26] EEG entropy monitoring, auditory evoked potentials, and several other systems such as the SNAP monitor and the Narcotrend monitor.

None of these systems are perfect. For example, they are unreliable at extremes of age (e.g., neonates, infants or the very elderly). Secondly, certain agents, such as nitrous oxide, may produce anesthesia without reducing the value of the depth monitor. [27] This is because the molecular action of these agents (NMDA receptor antagonists) differs from that of more conventional agents, and they suppress cortical EEG activity less. Third, they are prone to interference from other biological potentials (such as EMG), or external electrical signals (such as electrosurgery). This means that the technology that will reliably monitor depth of anesthesia for every patient and every anesthetic does not yet exist. This may in part explain why a 2016 systematic review and meta analysis concluded that depth-of-anesthesia monitors had a similar effect to standard clinical monitoring on the risk of awareness during surgery [28]

Incidence

The incidence of anesthesia awareness is variable; it seems to affect 0.2% to 0.4% of patients. This variation reflects the surgical setting as well as the physiological state of the patient; the incidence is 0.2% in general surgery, about 0.4% during caesarean section, between 1% and 2% during cardiac surgery and between 10% and 40% for anesthesia of the traumatized. [29] [30] [31] [32] [33] [34] [35] [36] [37] The majority of these do not feel pain, although around one-third did, in a range of experience from a sore throat caused by the endotracheal tube, to traumatic pain at the incision site. The incidence is halved in the absence of neuromuscular blockade. [37]

The quoted incidences are controversial as many cases of "awareness" are open to interpretation.

The incidence is higher and has more serious sequelae when muscle relaxants or neuromuscular-blocking drugs are used. [38] This is because without relaxant the patient will move and the anesthesiologist will then deepen the anesthesia.

One study has indicated that this phenomenon occurs in 0.13% of patients, or between 1 and 2 per 1000. [39] There are conflicting data, however, as another study suggested it is a rarer phenomenon, with an incidence of 0.0068%, after review of data from a population of 211,842 patients. [40]

Postoperative interview by an anesthetist is common practice to elucidate whether awareness occurred in the case. If awareness is reported, a case review is immediately performed to identify machine, medication, or operator error.[ citation needed ]

Outcomes

Patients who experience full awareness with explicit recall may have suffered an enormous trauma due to the extreme pain of surgery. Some patients experience post-traumatic stress disorder (PTSD), leading to long-lasting after-effects such as nightmares, night terrors, flashbacks, insomnia, and in some cases even suicide. [41] Some cases of awareness alert the patient to intra-operative errors.[ citation needed ]

A study from Sweden in 2002 attempted to follow up 18 patients for approximately 2 years after having been previously diagnosed with awareness under anesthesia. [42] Four of the nine interviewed patients were still severely disabled due to psychiatric/psychological after-effects. All of these patients had experienced anxiety during the period of awareness, but only one had stated feeling pain. Another three patients had less severe, transient mental symptoms, although they could cope with these in daily life. Two patients denied any lasting effects from their awareness episode.[ citation needed ]

Society and culture

Related Research Articles

<span class="mw-page-title-main">Anesthesia</span> State of medically-controlled temporary loss of sensation or awareness

Anesthesia or anaesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia, paralysis, amnesia, and unconsciousness. An individual under the effects of anesthetic drugs is referred to as being anesthetized.

<span class="mw-page-title-main">Isoflurane</span> General anaesthetic given via inhalation

Isoflurane, sold under the brand name Forane among others, is a general anesthetic. It can be used to start or maintain anesthesia; however, other medications are often used to start anesthesia, due to airway irritation with isoflurane. Isoflurane is given via inhalation.

<span class="mw-page-title-main">General anaesthesia</span> Medically induced loss of consciousness

General anaesthesia (UK) or general anesthesia (US) is a method of medically inducing loss of consciousness that renders a patient unarousable even with painful stimuli. This effect is achieved by administering either intravenous or inhalational general anaesthetic medications, which often act in combination with an analgesic and neuromuscular blocking agent. Spontaneous ventilation is often inadequate during the procedure and intervention is often necessary to protect the airway. General anaesthesia is generally performed in an operating theater to allow surgical procedures that would otherwise be intolerably painful for a patient, or in an intensive care unit or emergency department to facilitate endotracheal intubation and mechanical ventilation in critically ill patients. Depending on the procedure, general anaesthesia may be optional or required. Regardless of whether a patient may prefer to be unconscious or not, certain pain stimuli could result in involuntary responses from the patient that may make an operation extremely difficult. Thus, for many procedures, general anaesthesia is required from a practical perspective.

<span class="mw-page-title-main">Anesthesiology</span> Medical specialty concerned with anesthesia and perioperative care

Anesthesiology, anaesthesiology, or anaesthesia is the medical specialty concerned with the total perioperative care of patients before, during and after surgery. It encompasses anesthesia, intensive care medicine, critical emergency medicine, and pain medicine. A physician specialized in anesthesiology is called an anesthesiologist, anaesthesiologist, or anaesthetist, depending on the country. In some countries, the terms are synonymous, while in other countries, they refer to different positions and anesthetist is only used for non-physicians, such as nurse anesthetists.

<span class="mw-page-title-main">Spinal anaesthesia</span> Form of neuraxial regional anaesthesia

Spinal anaesthesia, also called spinal block, subarachnoid block, intradural block and intrathecal block, is a form of neuraxial regional anaesthesia involving the injection of a local anaesthetic or opioid into the subarachnoid space, generally through a fine needle, usually 9 cm (3.5 in) long. It is a safe and effective form of anesthesia usually performed by anesthesiologists that can be used as an alternative to general anesthesia commonly in surgeries involving the lower extremities and surgeries below the umbilicus. The local anesthetic with or without an opioid injected into the cerebrospinal fluid provides locoregional anaesthesia: true analgesia, motor, sensory and autonomic (sympathetic) blockade. Administering analgesics in the cerebrospinal fluid without a local anaesthetic produces locoregional analgesia: markedly reduced pain sensation, some autonomic blockade, but no sensory or motor block. Locoregional analgesia, due to mainly the absence of motor and sympathetic block may be preferred over locoregional anaesthesia in some postoperative care settings. The tip of the spinal needle has a point or small bevel. Recently, pencil point needles have been made available.

<span class="mw-page-title-main">Anesthetic</span> Drug that causes anesthesia

An anesthetic or anaesthetic is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into two broad classes: general anesthetics, which result in a reversible loss of consciousness, and local anesthetics, which cause a reversible loss of sensation for a limited region of the body without necessarily affecting consciousness.

<span class="mw-page-title-main">Allergic reactions to anesthesia</span> Medical condition

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<span class="mw-page-title-main">Bispectral index</span>

Bispectral index (BIS) is one of several technologies used to monitor depth of anesthesia. BIS monitors are used to supplement Guedel's classification system for determining depth of anesthesia. Titrating anesthetic agents to a specific bispectral index during general anesthesia in adults allows the anesthetist to adjust the amount of anesthetic agent to the needs of the patient, possibly resulting in a more rapid emergence from anesthesia. Use of the BIS monitor could reduce the incidence of intraoperative awareness during anaesthesia. The exact details of the algorithm used to create the BIS index have not been disclosed by the company that developed it.

<span class="mw-page-title-main">Remifentanil</span> Synthetic opioid analgesic

Remifentanil, marketed under the brand name Ultiva is a potent, short-acting synthetic opioid analgesic drug. It is given to patients during surgery to relieve pain and as an adjunct to an anaesthetic. Remifentanil is used for sedation as well as combined with other medications for use in general anesthesia. The use of remifentanil has made possible the use of high-dose opioid and low-dose hypnotic anesthesia, due to synergism between remifentanil and various hypnotic drugs and volatile anesthetics.

A post-anesthesia care unit (PACU) and sometimes referred to as post-anesthesia recovery or PAR, or simply recovery, is a part of hospitals, ambulatory care centers, and other medical facilities. Patients who received general anesthesia, regional anesthesia, or local anesthesia are transferred from the operating room suites to the recovery area. The patients are monitored typically by anesthesiologists, nurse anesthetists, and other medical staff. Providers follow a standardized handoff to the medical PACU staff that includes, which medications were given in the operating room suites, how hemodynamics were during the procedures, and what is expected for their recovery. After initial assessment and stabilization, patients are monitored for any potential complications, until the patient is transferred back to their hospital rooms.

Guedel's classification is a means of assessing the depth of general anesthesia introduced by Arthur Ernest Guedel (1883–1956) in 1920.

<span class="mw-page-title-main">Gantacurium chloride</span> Chemical compound

Gantacurium chloride is a new experimental neuromuscular blocking drug or skeletal muscle relaxant in the category of non-depolarizing neuromuscular-blocking drugs, used adjunctively in surgical anesthesia to facilitate endotracheal intubation and to provide skeletal muscle relaxation during surgery or mechanical ventilation. Gantacurium is not yet available for widespread clinical use: it is currently undergoing Phase III clinical development.

Neurosurgical anesthesiology, neuroanesthesiology, or neurological anesthesiology is a subspecialty of anesthesiology devoted to the total perioperative care of patients before, during, and after neurological surgeries, including surgeries of the central (CNS) and peripheral nervous systems (PNS). The field has undergone extensive development since the 1960s correlating with the ability to measure intracranial pressure (ICP), cerebral blood flow (CBF), and cerebral metabolic rate (CMR).

<span class="mw-page-title-main">History of general anesthesia</span>

Throughout recorded history, attempts at producing a state of general anesthesia can be traced back to the writings of ancient Sumerians, Babylonians, Assyrians, Egyptians, Indians, and Chinese. Despite significant advances in anatomy and surgical technique during the Renaissance, surgery remained a last-resort treatment largely due to the pain associated with it. However, scientific discoveries in the late 18th and early 19th centuries paved the way for the development of modern anesthetic techniques.

<span class="mw-page-title-main">Brachial plexus block</span>

Brachial plexus block is a regional anesthesia technique that is sometimes employed as an alternative or as an adjunct to general anesthesia for surgery of the upper extremity. This technique involves the injection of local anesthetic agents in close proximity to the brachial plexus, temporarily blocking the sensation and ability to move the upper extremity. The subject can remain awake during the ensuing surgical procedure, or they can be sedated or even fully anesthetized if necessary.

<span class="mw-page-title-main">Postoperative residual curarization</span> Medical condition

Postoperative residual curarization (PORC) or residual neuromuscular blockade (RNMB) is a residual paresis after emergence from general anesthesia that may occur with the use of neuromuscular-blocking drugs. Today residual neuromuscular blockade is defined as a train of four ratio of less than 0.9 when measuring the response to ulnar nerve stimulation at the adductor pollicis muscle using mechanomyography or electromyography. A meta-analysis reported that the incidence of residual neuromuscular paralysis was 41% in patients receiving intermediate neuromuscular blocking agents during anaesthesia. It is possible that > 100,000 patients annually in the USA alone, are at risk of adverse events associated with undetected residual neuromuscular blockade. Neuromuscular function monitoring and the use of the appropriate dosage of sugammadex to reverse blockade produced by rocuronium can reduce the incidence of postoperative residual curarization. In this study, with usual care group receiving reversal with neostigmine resulted in a residual blockade rate of 43%.

The following outline is provided as an overview of and topical guide to anesthesia:

<span class="mw-page-title-main">History of neuraxial anesthesia</span>

The history of neuraxial anaesthesia dates back to the late 1800s and is closely intertwined with the development of anaesthesia in general. Neuraxial anaesthesia, in particular, is a form of regional analgesia placed in or around the Central Nervous System, used for pain management and anaesthesia for certain surgeries and procedures.

Obstetric anesthesia or obstetric anesthesiology, also known as ob-gyn anesthesia or ob-gyn anesthesiology, is a sub-specialty of anesthesiology that provides peripartum pain relief (analgesia) for labor and anesthesia for cesarean deliveries ('C-sections').

Total intravenous anesthesia (TIVA) refers to the intravenous administration of anesthetic agents to induce a temporary loss of sensation or awareness. The first study of TIVA was done in 1872 using chloral hydrate, and the common anesthetic agent propofol was licensed in 1986. TIVA is currently employed in various procedures as an alternative technique of general anesthesia in order to improve post-operative recovery.

References

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  35. ↑ Lyons G, Macdonald R (January 1991). "Awareness during caesarean section". Anaesthesia. 46 (1): 62–4. doi: 10.1111/j.1365-2044.1991.tb09321.x . PMID   1996761. S2CID   45800761.
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  37. 1 2 Sebel PS, Bowdle TA, Ghoneim MM, Rampil IJ, Padilla RE, Gan TJ, Domino KB (September 2004). "The incidence of awareness during anesthesia: a multicenter United States study". Anesthesia and Analgesia. 99 (3): 833–9, table of contents. doi: 10.1213/01.ANE.0000130261.90896.6C . PMID   15333419. S2CID   7413819.
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  43. ↑ "Anesthesia (2006)". IMDb. Retrieved 2007-11-26.
  44. ↑ "Return (2007) – 리턴 @ HanCinema :: The Korean Movie and Drama Database". HanCinema. Archived from the original on 14 October 2007. Retrieved 2007-11-26.
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