Anesthesia awareness
Encyclopedia
Anesthesia awareness, or unintended intra-operative awareness occurs during general anesthesia
, on the operating table, when the patient has not been given enough of the general anesthetic or analgesic
to render the patient unconscious during general anesthesia (often when agents used to paralyze the patient have been administered). In brief, it is the post-operative recall of intra-operative events.
However, it can also occur in the post-anesthesia care unit (PACU) or in the intensive-care unit (ICU), where patients are kept sedated, tranquilized and sometimes paralyzed (and intubated) and are connected to life support systems, awaiting normalization of their physiology.
In some cases, post traumatic stress disorder (PTSD) may arise after intraoperative awareness, causing the patient to require counseling for an extended period.
The incidence of a state with both responses in diverse degrees is also possible. The drugs that induce paralysis would also prevent responding to commands.
The experiences of patients who have experienced anesthesia awareness vary widely depending on why they became aware, whether they were paralyzed and patient responses and sequela
e vary widely as well. It is unusual for someone having experienced awareness without pain or suffocation to suffer bad sequelae. The experience may be extremely traumatic for the patient or not at all depending on whether they could breathe and what errors were made.
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.
Under certain circumstances, a general anesthetic, whereby the patient is completely unconscious, may be unnecessary and/or undesirable. For instance, with a cesarean delivery, the goal is to provide comfort with neuraxial anesthetic yet maintain consciousness so that the mother can participate in the birth of her 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 monitored anesthesia care versus general anesthesia can be complex involving careful consideration of individual circumstances and after discussion with the patient as to their preferences.
Patients who undergo conscious sedation or monitored anesthesia care are never meant to be without recall. Whether or not a patient remembers the procedure depends on the type of medications used, the dosages used, patient physiology, and other factors. Many patients undergoing monitored anesthesia care do not remember the experience.
Several studies have indicated this occurs in about 1 or 2 per 1000. Other studies show a much lower incidence, usually because the anesthesiologists know they are in a trial and are very experienced. Some studies suggest it is a rare phenomenon, with rates varying from 0.13% to as low as 0.0068%.
Anesthesia equipment should always be checked prior to use but because of haste this does not always happen. Prompt inspection of the anesthesia equipment and record after a patient reports awareness must be done immediately and may help prevent future occurrences unless it was caused by human error (as it usually is). All drugs used and empty syringes must be carefully examined and tested because drug errors cause a high percentage of awareness cases. It is also important that a case of suspected awareness be communicated to the patient's healthcare team immediately, and that the event be scrutinized closely by senior anesthetic medical staff.
, and in some cases even suicide.
. Under general anesthesia, the patient's muscles may be paralyzed in order to facilitate tracheal intubation, surgical exposure, or mechanical ventilation
. The paralytic agent does not cause unconsciousness or take away the patient's ability to feel pain but it does prevent the patient from breathing so they must be ventilated correctly.
A fully paralyzed patient is unable to move, speak, blink the eyes, or otherwise respond to the pain. It is incorrect to think that physiological signs such as increased heart rate (tachycardia
), blood pressure (hypertension
), dilation of the pupils (mydriasis
), sweating (diaphoresis
), and the formation of tears (lacrimation) will continue to occur normally in response to pain in the anesthetized state. If neuromuscular blocking drugs are used this causes skeletal muscle paralysis and often interfere with the functioning of the autonomic nervous system
. The patient cannot signal their distress and they may not exhibit the signs of awareness that would be expected to be detectable by clinical vigilance.
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 correlate with full awareness but is a sign that the anesthesia is light. Even without the use of paralytics the absence of movement does not necessarily correlate with amnesia.
, or in hypovolemic patients or patients with minimal cardiac reserve, the anesthesia provider may aim to provide "light anesthesia" and should discuss this with the patient 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, causing 'awareness' in the anesthetized subject.
s with volatile anesthetic. Other causes of awareness include unfamiliarity with techniques used, e.g. intravenous anesthetic regimes, or 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
recently 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
.
Machine malfunction or misuse may result in an inadequate delivery of anesthetic. Many Boyle's machines used in many 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 leaves, causes some cases of awareness and death.
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.
. Some patients may be more resistant to the effects of anesthetics than others, women need more anesthetic than men, there are several possible reasons for this, e.g. less alcohol consumption, female hormones, different fat distribution in the body, but nobody has researched this. Younger age, obesity, tobacco smoking, or long-term use of certain drugs (alcohol
, opiate
s, or amphetamine
s) may increase the anesthetic dose needed to produce unconsciousness but often this is used as an excuse for poor technique. 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.
, which represents the electrical activity of the cerebral cortex
, which is active when awake but quiescent when anesthetized (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), 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
, ketamine
or xenon
, may produce anesthesia without reducing the value of the depth monitor. 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. Thirdly, 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.
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. 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 deny it. 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 anesthesia awareness does not commonly occur in minor surgeries. It occurs more frequently in more serious surgeries.
Dr. John F. Kihlstrom of the University of California, Berkeley is one such cognitive psychologists and he has contributed to a book on consciousness with a chapter on anesthesia.
Dr. Chantal Kerssens, Ph.D. of Emory University in Atlanta was trained as a cognitive psychologist (MS, PhD). Her research interests have been in memory function during anesthesia, in particular its relation to depth of sedation.1 She can be observed in a video lecture whose topic is: Neuroimaging Anesthetic Effect on Brain Networks. 2
Professor Jackie Andrade of the Applied Psychology Group at University of Plymouth, U.K. has a special interest in “Priming and awareness during anaesthesia”. 3 An abstract of an article she has written with a title “Unconscious memory formation during anaesthesia” can be assessed from the footnote link. 4
Dr. Phil Merikle, Distinguished Professor Emeritus of the Department of Psychology, University of Waterloo, Ontario, Canada has written and published on the subject of “Memory and Anaesthesia”.5 He coauthored an influential meta-analysis article in this area in 1996 in a journal entitled Consciousness and Cognition.6
Dr. Daniel L. Schacter former Chair, Department of Psychology, Harvard University 7 has been actively concerned with this topic since at least 1990, when he published a book chapter entitled: “Anesthesia, amnesia, and the cognitive unconscious”. In the same year he published a journal article entitled “Implicit and Explicit Memory Following Surgical Anesthesia”. 8
General anaesthetic
A general anaesthetic is a drug that brings about a reversible loss of consciousness. These drugs are generally administered by an anaesthesia provider to induce or maintain general anaesthesia to facilitate surgery...
, on the operating table, when the patient has not been given enough of the general anesthetic or analgesic
Analgesic
An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....
to render the patient unconscious during general anesthesia (often when agents used to paralyze the patient have been administered). In brief, it is the post-operative recall of intra-operative events.
However, it can also occur in the post-anesthesia care unit (PACU) or in the intensive-care unit (ICU), where patients are kept sedated, tranquilized and sometimes paralyzed (and intubated) and are connected to life support systems, awaiting normalization of their physiology.
Background
Awareness occurs in 20,000–40,000 patients out of the 20 million US surgeries performed each year (between 0.1% and 0.2%) when patients have anesthesia that is inadequate to keep them unconscious during an operation. Large trials have demonstrated that around 1 to 2 per 1000 patients experience some form of awareness. The majority of these do not feel pain although around one third did, be it a sore throat from an endotracheal tube or pain from the incision site. The incidence is halved in the absence of neuro-muscular blockade. In this situation, the patient may feel the pain or pressure of surgery, hear conversations, or feel as if they cannot breathe. The patient may be unable to communicate any distress because they have been given a paralytic/muscle relaxant; without this, they can move and the anesthesiologists are alerted and provide more anesthetic drugs to render the patient unconscious again. If anesthesia awareness does occur, about 42% feel the pain of the operation, 94% experience panic/anxiety (sometimes because they cannot breathe), and 70% experience lasting psychological symptoms. The quoted incidences are highly controversial as many cases of "awareness" are open to interpretation; only a small number are irrefutably so. These usually involve feeling severe pain, or clear recall of the conversations of the operating room staff. Some anesthetic drugs may cause vivid dreams in the period before going to sleep, which may be interpreted as "being awake". 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"In some cases, post traumatic stress disorder (PTSD) may arise after intraoperative awareness, causing the patient to require counseling for an extended period.
Awareness and recall
There are two states of consciousness that may be present:- Awareness: That is, patients seem to be cognizant responding to commands but with no postoperative recall or memory of the events.
- Memorization and recall: That is, patients can recall events postoperatively, but were not necessarily conscious enough to respond to commands.
The incidence of a state with both responses in diverse degrees is also possible. The drugs that induce paralysis would also prevent responding to commands.
The experience of anesthesia awareness
The most traumatic case of anesthesia awareness is full consciousness during surgery with pain and explicit recall of intraoperative events. In less severe cases, patients may have only poor recollection of conversations, events, pain, pressure, or difficulty in breathing. Some cases of difficulty in breathing are caused by intubation errors and/or problems with the ventilator and a patient might be suffocating.The experiences of patients who have experienced anesthesia awareness vary widely depending on why they became aware, whether they were paralyzed and patient responses and sequela
Sequela
A sequela) is a pathological condition resulting from a disease, injury, or other trauma.Chronic kidney disease, for example, is sometimes a sequela of diabetes, and neck pain is a common sequela of whiplash or other trauma to the cervical vertebrae. Post-traumatic stress disorder may be a...
e vary widely as well. It is unusual for someone having experienced awareness without pain or suffocation to suffer bad sequelae. The experience may be extremely traumatic for the patient or not at all depending on whether they could breathe and what errors were made.
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.
Conscious sedation and monitored anesthesia care
There are various levels of consciousness. Wakefulness and general anesthesia are 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. It is important to note that awareness/wakefulness is not necessarily correlated with pain or discomfort. The aim of conscious sedation or monitored anesthetic care 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 and/or undesirable. For instance, with a cesarean delivery, the goal is to provide comfort with neuraxial anesthetic yet maintain consciousness so that the mother can participate in the birth of her 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 monitored anesthesia care versus general anesthesia can be complex involving careful consideration of individual circumstances and after discussion with the patient as to their preferences.
Patients who undergo conscious sedation or monitored anesthesia care are never meant to be without recall. Whether or not a patient remembers the procedure depends on the type of medications used, the dosages used, patient physiology, and other factors. Many patients undergoing monitored anesthesia care do not remember the experience.
Incidence
The incidence of anesthesia awareness is higher when muscle relaxants are used. This is because without relaxant the patient will move and the anesthesiologist will deepen the anesthesia.Several studies have indicated this occurs in about 1 or 2 per 1000. Other studies show a much lower incidence, usually because the anesthesiologists know they are in a trial and are very experienced. Some studies suggest it is a rare phenomenon, with rates varying from 0.13% to as low as 0.0068%.
Anesthesia equipment should always be checked prior to use but because of haste this does not always happen. Prompt inspection of the anesthesia equipment and record after a patient reports awareness must be done immediately and may help prevent future occurrences unless it was caused by human error (as it usually is). All drugs used and empty syringes must be carefully examined and tested because drug errors cause a high percentage of awareness cases. It is also important that a case of suspected awareness be communicated to the patient's healthcare team immediately, and that the event be scrutinized closely by senior anesthetic medical staff.
Outcomes
Patients who experience full awareness with explicit recall may have suffered an enormous trauma. Some patients experience post traumatic stress disorder (PTSD), leading to long-lasting after-effects such as nightmares, night terrors, flashbacks, insomniaInsomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...
, and in some cases even suicide.
Paralytics/muscle relaxant use
The biggest risk factor is the use of a medication that induces muscle paralysis, such as SuxamethoniumSuxamethonium chloride
Suxamethonium chloride , also known as suxamethonium or succinylcholine, is a paralytic drug used to induce muscle relaxation and short-term paralysis, usually to facilitate tracheal intubation. Suxamethonium is sold under the trade names Anectine, Quelicin, and Scoline. It is used as a paralytic...
. Under general anesthesia, the patient's muscles may be paralyzed in order to facilitate tracheal intubation, surgical exposure, or mechanical ventilation
Mechanical ventilation
In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...
. The paralytic agent does not cause unconsciousness or take away the patient's ability to feel pain but it does prevent the patient from breathing so they must be ventilated correctly.
A fully paralyzed patient is unable to move, speak, blink the eyes, or otherwise respond to the pain. It is incorrect to think that physiological signs such as increased heart rate (tachycardia
Tachycardia
Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...
), blood pressure (hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
), dilation of the pupils (mydriasis
Mydriasis
Mydriasis is a dilation of the pupil due to disease, trauma or the use of drugs. Normally, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day...
), sweating (diaphoresis
Diaphoresis
Diaphoresis is excessive sweating commonly associated with shock and other medical emergency conditions.Diaphoretic is the state of perspiring profusely, or something that has the power to cause increased perspiration....
), and the formation of tears (lacrimation) will continue to occur normally in response to pain in the anesthetized state. If neuromuscular blocking drugs are used this causes skeletal muscle paralysis and often interfere with the functioning of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
. The patient cannot signal their distress and they may not exhibit the signs of awareness that would be expected to be detectable by clinical vigilance.
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 correlate with full awareness but is a sign that the anesthesia is light. Even without the use of paralytics the absence of movement does not necessarily correlate with amnesia.
Light anesthesia
For certain operations, such as Cesarean sectionCaesarean section
A Caesarean section, is a surgical procedure in which one or more incisions are made through a mother's abdomen and uterus to deliver one or more babies, or, rarely, to remove a dead fetus...
, or in hypovolemic patients or patients with minimal cardiac reserve, the anesthesia provider may aim to provide "light anesthesia" and should discuss this with the patient 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
Hypotension
In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...
) but, causing 'awareness' in the anesthetized subject.
Improper equipment maintenance or anesthesiologist error
Human errors include oesophageal intubation, inadequate drug dose, drug given by the wrong route or wrong drug given, drugs given in the wrong sequence, inadequate monitoring, disconnections and kinks in tubes from the ventilator, and failure to refill the anesthetic machine's vaporizerAnaesthetic vaporiser
An anaesthetic vaporiser is a device generally attached to an anaesthetic machine which delivers a given concentration of a volatile anaesthetic agent.The design of these devices takes account of varying*ambient temperature*fresh gas flow...
s with volatile anesthetic. Other causes of awareness include unfamiliarity with techniques used, e.g. intravenous anesthetic regimes, or 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
American Society of Anesthesiologists
The American Society of Anesthesiologists is an association of physicians, primarily anesthesiologists, that share a common goal of raising the standard of the medical specialty of anesthesiology and the improvement of patient care by fostering and encouraging education through research and...
recently 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
Australian and New Zealand College of Anaesthetists
The Australian and New Zealand College of Anaesthetists is responsible for examining and qualifying anaesthetists in Australia and New Zealand. The College maintains standards of practice in anaesthesia.-Membership:...
.
Machine malfunction or misuse may result in an inadequate delivery of anesthetic. Many Boyle's machines used in many 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
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
cylinder
Gas cylinder
A gas cylinder is a pressure vessel used to store gases at above atmospheric pressure. High pressure gas cylinders are also called bottles. Although they are sometimes colloquially called "tanks", this is technically incorrect, as a tank is a vessel used to store liquids at ambient pressure and...
) or a malfunctioning intravenous pump or disconnection of its delivery tubing. Patient abandonment, when the anesthesiologist leaves, causes some cases of awareness and death.
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
Bispectral index
Bispectral index is one of several technologies which purport to monitor depth of anesthesia. BIS monitors are intended to replace or supplement Guedel's classification system for determining depth of anesthesia...
, should not be used in isolation.
Patient physiology
Rare causes of awareness include drug tolerance, or a tolerance induced by the interaction of other drugsMedication
A pharmaceutical drug, also referred to as medicine, medication or medicament, can be loosely defined as any chemical substance intended for use in the medical diagnosis, cure, treatment, or prevention of disease.- Classification :...
. Some patients may be more resistant to the effects of anesthetics than others, women need more anesthetic than men, there are several possible reasons for this, e.g. less alcohol consumption, female hormones, different fat distribution in the body, but nobody has researched this. Younger age, obesity, tobacco smoking, or long-term use of certain drugs (alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
, opiate
Opiate
In medicine, the term opiate describes any of the narcotic opioid alkaloids found as natural products in the opium poppy plant.-Overview:Opiates are so named because they are constituents or derivatives of constituents found in opium, which is processed from the latex sap of the opium poppy,...
s, or amphetamine
Amphetamine
Amphetamine or amfetamine is a psychostimulant drug of the phenethylamine class which produces increased wakefulness and focus in association with decreased fatigue and appetite.Brand names of medications that contain, or metabolize into, amphetamine include Adderall, Dexedrine, Dextrostat,...
s) may increase the anesthetic dose needed to produce unconsciousness but often this is used as an excuse for poor technique. 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
Red hair
Red hair occurs on approximately 1–2% of the human population. It occurs more frequently in people of northern or western European ancestry, and less frequently in other populations...
. Marked anxiety prior to the surgery can increase the amount of anesthesia required to prevent recall.
Prevention
The risk of awareness is reduced by simple steps and good clinical practice: well-trained personnel; avoidance of paralytics unless necessary; careful checking of drugs, doses and equipment; good monitoring, and careful vigilance during the case.Monitors
Recent advances have led to the manufacture of monitors of awareness. Typically these monitor the EEGElectroencephalography
Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
, which represents the electrical activity of the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
, which is active when awake but quiescent when anesthetized (or in natural sleep
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...
). 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
Bispectral index
Bispectral index is one of several technologies which purport to monitor depth of anesthesia. BIS monitors are intended to replace or supplement Guedel's classification system for determining depth of anesthesia...
(BIS), EEG entropy monitoring
Entropy monitoring
Entropy monitoring is a relatively new method of assessing anaesthetic depth. It was commercially developed by Datex-Ohmeda, now part of GE Healthcare.It relies on a method of assessing the degree of irregularity in electroencephalogram signals...
, 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
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
, ketamine
Ketamine
Ketamine is a drug used in human and veterinary medicine. Its hydrochloride salt is sold as Ketanest, Ketaset, and Ketalar. Pharmacologically, ketamine is classified as an NMDA receptor antagonist...
or xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
, may produce anesthesia without reducing the value of the depth monitor. This is because the molecular action of these agents (NMDA
NMDA
N-Methyl-D-aspartic acid or N-Methyl-D-aspartate is an amino acid derivative which acts as a specific agonist at the NMDA receptor mimicking the action of glutamate, the neurotransmitter which normally acts at that receptor...
receptor antagonists) differs from that of more conventional agents, and they suppress cortical EEG activity less. Thirdly, they are prone to interference from other biological potentials (such as EMG
Electromyography
Electromyography is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle...
), or external electrical signals (such as electrosurgery
Electrosurgery
Electrosurgery is the application of a high-frequency electric current to biological tissue as a means to cut, coagulate, desiccate, or fulgurate tissue. . Its benefits include the ability to make precise cuts with limited blood loss...
). This means that the technology that will reliably monitor depth of anesthesia for every patient and every anesthetic does not yet exist.
Controversies
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. Four of the nine interviewed patients were still severely disabled due to psychiatric/psychological sequelae. 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 sequelae from their awareness episode.Remembrance
New research has been carried out to test what people can remember after a general anesthetic in an effort to more clearly understand anesthesia awareness and help to protect patients from experiencing it. A memoryMemory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
is not one simple entity; it is a system of many intricate details and networks.
Memory is currently classified under two main subsections.
- First there is explicit or conscious memory, which refers to the conscious recollection of previous experiences. An example of explicit memory is remembering what you did last weekend. When it comes to an anesthetized patient, a doctor may ask the patient after undergoing general anesthesia if he or she could remember hearing any distinct sounds or words while under anesthesia. This approach is called a "recall test" because patients are asked to recall any memories they had during surgery.
- The second main type of memory is implicit memory or unconscious memory, which refers to the changes in performance or behavior that are produced by previous experiences but without any conscious recollection of those experiences. An example of this is a recognition test, where patients are asked to determine, after surgery, which of a selection of words could be heard to during the surgery. The following scenario is an example. Patients were exposed during anesthesia to a list of words containing the word "pension". Postoperatively, when they were presented with the three-letter word stem PEN___ and were asked to supply the first word that came to their minds beginning with those letters, they gave the word "pension" more often than "pencil" or "peninsula" or others.
Some researchers are now formally interviewing patients postoperatively to calculate the incidence of anesthesia awareness. 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 deny it. 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 anesthesia awareness does not commonly occur in minor surgeries. It occurs more frequently in more serious surgeries.
Cognitive psychologists study memory under anesthesia
A number of mainstream cognitive psychologists have studied memory as a basic cognitive process under anesthesia.Dr. John F. Kihlstrom of the University of California, Berkeley is one such cognitive psychologists and he has contributed to a book on consciousness with a chapter on anesthesia.
Dr. Chantal Kerssens, Ph.D. of Emory University in Atlanta was trained as a cognitive psychologist (MS, PhD). Her research interests have been in memory function during anesthesia, in particular its relation to depth of sedation.1 She can be observed in a video lecture whose topic is: Neuroimaging Anesthetic Effect on Brain Networks. 2
Professor Jackie Andrade of the Applied Psychology Group at University of Plymouth, U.K. has a special interest in “Priming and awareness during anaesthesia”. 3 An abstract of an article she has written with a title “Unconscious memory formation during anaesthesia” can be assessed from the footnote link. 4
Dr. Phil Merikle, Distinguished Professor Emeritus of the Department of Psychology, University of Waterloo, Ontario, Canada has written and published on the subject of “Memory and Anaesthesia”.5 He coauthored an influential meta-analysis article in this area in 1996 in a journal entitled Consciousness and Cognition.6
Dr. Daniel L. Schacter former Chair, Department of Psychology, Harvard University 7 has been actively concerned with this topic since at least 1990, when he published a book chapter entitled: “Anesthesia, amnesia, and the cognitive unconscious”. In the same year he published a journal article entitled “Implicit and Explicit Memory Following Surgical Anesthesia”. 8
Cultural references
- AwakeAwake (film)Awake is a 2007 American crime/supernatural/conspiracy thriller written and directed by Joby Harold. It stars Hayden Christensen, Jessica Alba, Terrence Howard and Lena Olin. The film was released in the United States and Canada on November 30, 2007....
, a 2007 film about anesthetic awareness - Anesthesia, an award-winning horror film about anesthesia awareness.
- Return, a Korean thriller movie about anesthesia awareness.
- In an episode of Nip/TuckNip/TuckNip/Tuck is an American drama series created by Ryan Murphy, which aired on FX in the United States. The series focuses on McNamara/Troy, a plastic surgery practice, and follows its founders, Sean McNamara and Christian Troy...
a woman, Rhea Reynolds, experiences anesthesia awareness while having surgery to repair scarring on her face. - Under: a 2006 film about anesthetic awareness
- Hannah MontanaHannah MontanaHannah Montana is an American television series, which debuted on March 24, 2006 on the Disney Channel. The series focuses on a girl who lives a double life as an average teenage school girl named Miley Stewart by day and a famous pop singer named Hannah Montana by night, concealing her real...
, Ones that Miley,experiences anesthesia awareness while having surgery to repair her leg .
See also
- Anesthetic machineAnaesthetic machineThe anaesthetic machine is used by anaesthesiologists and nurse anaesthetists to support the administration of anaesthesia...
- Carol WeihrerCarol WeihrerCarol Weihrer is an activist for victims of anesthesia awareness. Beginning in 1989, Weiher suffered chronic pain from recurrent corneal erosion syndrome. After 14 unsuccessful surgeries to relieve the increasing severity of the pain, in 1998 she underwent an eye removal surgery and reportedly...
- Iatrogenic
- Awake (film)Awake (film)Awake is a 2007 American crime/supernatural/conspiracy thriller written and directed by Joby Harold. It stars Hayden Christensen, Jessica Alba, Terrence Howard and Lena Olin. The film was released in the United States and Canada on November 30, 2007....
External links
- interactive site for those with an interest in awareness includes short videos telling one woman's story
- Anaesthetic Awareness Network UK & Ireland – was a support base for Anaesthetic Awareness patients in Europe, site has not been updated since 2008
- American Society of Anesthesiologists at asahq.org
- Doctor Evidence Intraoperative Awareness Database an authoritative database based on ALL published anesthesia awareness data
- Resource for Student & Working Nurse Anesthetists at nurse-anesthesia.org
- Resource for Physiology and Pharmacology at Stanford UniversityStanford UniversityThe Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
- Anesthesia Awareness Registry -Anesthesia Awareness Registry where people who have experienced awareness can register to share their perspective