This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages)(Learn how and when to remove this template message)
Anesthesia awareness, also referred to as accidental awareness during general anaesthesia (AAGA) or unintended intra-operative awareness, is a potential complication occurring during general anesthesia where the intended state of complete unconsciousness is not maintained throughout the whole procedure. It can occur either because of failure to deliver sufficient anesthetic medication to the patient's body or because of individual patient factors that mean the patient is resistant to what would normally be an adequate dose of anesthetic medication.
- 1 Background
- 2 Awareness and recall
- 3 Experiences
- 4 Conscious sedation and monitored anesthesia care
- 5 Incidence
- 6 Outcomes
- 7 Causes and Risk Factors
- 8 Prevention
- 9 Monitors
- 10 Memory
- 11 Cognitive psychologists study memory under anesthesia
- 12 Cultural references
- 13 See also
- 14 References
- 15 External links
AAGA is an infrequent but extremely frightening event where the patient is unintentionally responsive during their surgical procedure and later recalls the episode. Its potentially distressing consequences and long-term psychological sequelae may affect the daily life of the patient  Awareness occurs when patients have anesthesia that is inadequate to keep them unconscious during an operation. The incidence of this anesthesia complication is variable and seems to affect 0.2% to 0.4% of patients according to the surgical setting carried out. This variation reflects the surgical setting as well as the physiological state of the patient. Thus, 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. The majority of these do not feel pain although around one third did, in a range of experience from a sore throat due to the endotracheal tube, to traumatic pain at 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 conversation, experience air hunger, or have difficulty breathing. The patient may be unable to communicate any distress because they have been given a 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 or anxiety, and 70% experience lasting symptoms which may be psychological and may be physical or neurological. The quoted incidences are controversial as many cases of "awareness" are open to interpretation. These usually involve feeling severe pain, clear recall of the conversations of the operating room staff or suffocation. 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. Sometimes neurological and brain injuries caused during the operation are wrongly diagnosed and described as PTSD.
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.
- Awareness 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 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 sequelae 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. Awareness/wakefulness does not necessarily imply 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 do not remember the experience.
The incidence of anesthesia awareness is higher and has more serious sequelae when muscle relaxants or neuromuscular-blocking drugs are used. This is because without relaxant the patient will move and the anesthesiologist will deepen the anesthesia.
One study has indicated this phenomenon occurs in about 1 or 2 per 1000 patients or 0.13%. There is conflicting data however as another study suggested it is a rare phenomenon, with an incidence of 0.0068% after review of their data from a patient population of 211,842 patients.
Post operative interview by an anesthetist is common practice to elucidate if awareness occurred in the case. If awareness is reported a case review is immediately performed to identify machine, medication, or operator error.
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, insomnia, and in some cases even suicide. Some cases of awareness alert the patient to intra-operative errors.
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 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.
Causes and Risk Factors
Paralytics/muscle relaxant use
The biggest risk factor is anaesthesia performed by unsupervised trainees and the use of a medication that induces muscle paralysis, such as Suxamethonium. Under general anesthesia, the patient's muscles may be paralyzed in order to facilitate tracheal intubation, surgical exposure, and because the patient cannot breathe for him or herself mechanical ventilation must be used. 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. If neuromuscular blocking drugs are used this causes skeletal muscle paralysis and interferes 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 imply full awareness but is a sign that the anesthesia is light. Even without the use of paralytics the absence of movement does not necessarily imply amnesia.
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 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.
Improper equipment maintenance or anesthesiologist error
Human errors include repeated attempts at intubation during which the short-acting anesthesic may wear off but the paralysing drug has not, oesophageal intubation, inadequate drug dose, drug given by the wrong route or 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 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.
Current research attributes the incidence of AAGA to a combination of the risks mentioned above, together with ineffective practice from ODPs, anaesthetic nurses, HCAs and anaesthetists . The main failures include: • Inattention or judgement errors related to drugs and volatile agents • Termination of anaesthesia 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 vaporisers (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 organisational or individual circumstances (bringing attention to staff shortage and stressful work environment) • Distractions caused by another member of staff
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 but this is often 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.
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. The technique is considered a reference standard by which other means of assessing consciousness can be assessed.
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 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, 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.
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 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. 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 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.
Cognitive psychologists study memory under anesthesia
A number of mainstream cognitive psychologists have studied memory as a basic cognitive process under anesthesia.
John F. Kihlstrom of the University of California, Berkeley is a cognitive psychologist and has contributed to a book on consciousness with a chapter on anesthesia.
Chantal Kerssens of Emory University in Atlanta was trained as a cognitive psychologist. Her research interests have been in memory function during anesthesia, in particular its relation to depth of sedation. She can be observed in a video lecture whose topic is: Neuroimaging Anesthetic Effect on Brain Networks.
Jackie Andrade of the Applied Psychology Group at University of Plymouth, U.K. has a special interest in "Priming and awareness during anaesthesia". She has written an article, "Unconscious memory formation during anaesthesia".
Phil Merikle of the Department of Psychology, University of Waterloo, Ontario, Canada has written and published on the subject of "Memory and Anaesthesia". He coauthored a meta-analysis Consciousness and Cognition.
Daniel L. Schacter former Chair, Department of Psychology, Harvard University published a book chapter, in 1990, entitled: “Anesthesia, amnesia, and the cognitive unconscious” and a journal article entitled “Implicit and Explicit Memory Following Surgical Anesthesia”.
- Awake, 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/Tuck a woman, Rhea Reynolds, experiences anesthesia awareness while having surgery to repair scarring on her face.
- Under: a 2006 film about anesthetic awareness
- 2014 Bollywood movie Heartless – the patient experienced full awareness during heart transplant.
- 2016 episode of Shortland Street, a New Zealand hospital soap opera, the patient experienced full awareness during facelift
- Almeida, Debora (Dec 2015). "Awake and unable to move: what can perioperative practitioners do to avoid accidental awareness under general anaesthesia?". Journal of Perioperative Practice. 25 (12): 257–261.
- Sebel PS (2004). "The incidence of awareness during anesthesia: A multicenter United States study". Anesth Analg. 99 (3): 833–9. doi:10.1213/01.ane.0000130261.90896.6c. PMID 15333419.
- Bogetz MS, Katz JA (1984). "Recall of surgery for major trauma". Anesthesiology. 61 (1): 6–9. doi:10.1097/00000542-198461010-00003. PMID 6742485.
- Bogod D, Orton J, Oh T (1990). "Detecting awareness during general anaesthetic caesarean section". Anaesthesia. 45 (4): 279–84. doi:10.1111/j.1365-2044.1990.tb14732.x. PMID 2337210.
- Dowd NP, Cheng DC, Karski JM, et al. (1998). "Intraoperative awareness in fast-track cardiac anesthesia". Anesthesiology. 89 (5): 1068–73. doi:10.1097/00000542-199811000-00006.
- Goldmann L, Shah MV, Hebden MW (1987). "Memory of cardiac anaesthesia". Anaesthesia. 42 (6): 596–603. doi:10.1111/j.1365-2044.1987.tb03082.x. PMID 3618993.
- Liu WH, Thorp TA, Graham SG, et al. (1991). "Incidence of awareness with recall during general anaesthesia". Anaesthesia. 46 (6): 435–7. doi:10.1111/j.1365-2044.1991.tb11677.x. PMID 2048657.
- Lyons G, Macdonald R. Awareness during Caesarean Section" Anaesthesia 1991; 46: 62-4.
- Sandin RH, Enlund G, Samuelsson P (2000). "Awareness during anaesthesia: a prospective case study". Lancet. 355 (9205): 707–711. doi:10.1016/s0140-6736(99)11010-9. PMID 10703802.
- Sebels PS, Bowdie TA, Ghoneim MM (2004). "The incidence of awareness during anaesthesia: a multi- centre United States study". Anesthesia and Analgesia. 99 (3): 833–839. doi:10.1213/01.ANE.0000130261.90896.6C. PMID 15333419.
- N. Moerman et al., Anesthesiology;79:454–464, 1993
- Osterman JE, Hopper J, Heran WJ, Keane TM, van der Kolk BA (2001). "Awareness under anesthesia and the development of posttraumatic stress disorder". Gen Hosp Psychiatry. 23 (4): 198–204. doi:10.1016/S0163-8343(01)00142-6. PMID 11543846.
- Ghoneim, Mohamed M (2001). Awareness during anesthesia. Butterworth Heinemann. p. 2. ISBN 0-7506-7201-3.
- Gajwani P, Muzina D, Gao K, Calabrese JR (2006). "Awareness under anesthesia during electroconvulsive therapy treatment". J ECT. 22 (2): 158–9. doi:10.1097/00124509-200606000-00018. PMID 16801837.
- Morgan, Jr. Clinical Anesthesiology. Mc Graw Hill. p. 291. ISBN 0-07-142358-3.
- Lekprasert, Varinee:"PreAnesthetic Assessment of the Patient Who Reports Previous Intraoperative Awareness", Anesthesiology News, June 2008, pages 35–38, www.AnesthesiologyNews.com.[full citation needed]
- Schneider G (2003). "[Intraoperative awareness]". Anasthesiol Intensivmed Notfallmed Schmerzther (in German). 38 (2): 75–84. doi:10.1055/s-2003-36993. PMID 12557119.
- Sebel, PS; Bowdle, TA; Ghoneim, MM; Rampil, IJ; Padilla, RE; Gan, TJ; Domino, KB (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.
- Pollard RJ, Coyle JP, Gilbert RL, Beck JE (2007). "Intraoperative awareness in a regional medical system: a review of 3 years' data". Anesthesiology. 106 (2): 269–74. doi:10.1097/00000542-200702000-00014. PMID 17264720.
- Breen, Tom (April 10, 2007). "Lawsuit: Wide-Awake Surgery Led to Death". Fox News Channel. CHARLESTON, W.Va. Retrieved 2009-09-04.
- Lennmarken C, Bildfors K, Enlund G, Samuelsson P, Sandin R (2002). "Victims of awareness". Acta anaesthesiologica Scandinavica. 46 (3): 229–31. doi:10.1034/j.1399-6576.2002.t01-1-460301.x. PMID 11939910.
- Lobato, Emilio B.; Nikolaus Gravenstein; Robert R. Kirby (2007). Complications in anesthesiology (3rd ed.). Lippincott Williams & Wilkins. p. 57. ISBN 0-7817-8263-5.
- "ANZCA – ANZCA". Archived from the original on 2007-10-14. Retrieved 2007-11-26.
- Almeida, Debora (December 2015). "Awake and unable to move: what can perioperative practitioners do to avoid accidental awareness under general anaesthesia?". Journal of Perioperative Practice. 25 (12): 257–261. Retrieved 7 December 2018.
- Liem EB, Lin CM, Suleman MI, et al. (2004). "Anesthetic requirement is increased in redheads". Anesthesiology. 101 (2): 279–283. doi:10.1097/00000542-200408000-00006. PMC 1362956. PMID 15277908.
- Tunstall, M. E. (1977). "Detecting wakefulness during general anaesthesia for caesarean section". British Medical Journal. 1 (6072): 1321. doi:10.1136/bmj.1.6072.1321-a. PMC 1607133. PMID 861598.
- Russell, I. F. (1986). "Comparison of wakefulness with two anaesthetic regimens. Total i.v. V. Balanced anaesthesia". British Journal of Anaesthesia. 58 (9): 965–8. doi:10.1093/bja/58.9.965. PMID 3756056.
- Jessop, J; Jones, JG (June 1991). "Conscious awareness during general anaesthesia--what are we attempting to monitor?". British Journal of Anaesthesia. 66 (6): 635–7. doi:10.1093/bja/66.6.635. PMID 2064875. Retrieved 15 December 2014.
- Veselis, RA (March 2006). "The remarkable memory effects of propofol". British Journal of Anaesthesia. 96 (3): 289–91. doi:10.1093/bja/ael016. PMID 16467436.
- Myles PS, Leslie K, McNeil J, Forbes A, Chan MT (2004). "Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware randomised controlled trial" (PDF). Lancet. 363 (9423): 1757–63. doi:10.1016/s0140-6736(04)16300-9. PMID 15172773.
- Clapcich AJ, Emerson RG, Roye DP, Xie H, Gallo EJ, Dowling KC, Ramnath B, Heyer EJ (2004). "The Effects of Propofol, Small-Dose Isoflurane, and Nitrous Oxide on Cortical Somatosensory Evoked Potential and Bispectral Index Monitoring in Adolescents Undergoing Spinal Fusion". Anesthesia and Analgesia. 99 (5): 1334-contents. doi:10.1213/01.ANE.0000134807.73615.5C. PMC 2435242. PMID 15502027.
- Sandin R (2006). "Outcome after awareness with explicit recall". Acta Anaesthesiol Belg. 57 (4): 429–32. PMID 17236646.
- Ghoneim MM; Weiskopf, Richard B. (2000). "Awareness during anesthesia". Anesthesiology. 92 (2): 597–602. doi:10.1097/00000542-200002000-00043. PMID 10691248.
- "Anesthesia (2007)". Retrieved 2010-05-29.
- "Emory University - Leading Research University in Atlanta, GA". www.med.emory.edu.
- "Chantal Kerssens PhD - SMPH Video Library". videos.med.wisc.edu.
- "Professor Jackie Andrade - University of Plymouth". www.plymouth.ac.uk.
- "Archived copy". Archived from the original on 2010-04-26. Retrieved 2010-06-12.
- "Archived copy" (PDF). Archived from the original (PDF) on 2009-12-29. Retrieved 2010-06-12.
- "Archived copy". Archived from the original on 2010-08-18. Retrieved 2010-08-17.
- Kihlstrom, John F.; Schacter, Daniel L.; Cork, Randall C.; Hurt, Catherine A.; Behr, Steven E. (1 September 1990). "Implicit and Explicit Memory following Surgical Anesthesia". Psychological Science. 1 (5): 303–306. doi:10.1111/j.1467-9280.1990.tb00222.x – via SAGE Journals.
- "Anesthesia (2006)". IMDb. Retrieved 2007-11-26.
- "Return (2007) – 리턴 @ HanCinema :: The Korean Movie and Drama Database". HanCinema. Archived from the original on 14 October 2007. Retrieved 2007-11-26.
- American Association of Nurse Anesthetists Awareness Brochure at aana.com
- American Association of Nurse Anesthestist Awareness Fact Sheet at aana.com
- American Society of Anesthesiologists at asahq.org
- Resource for Student & Working Nurse Anesthetists at nurse-anesthesia.org
- Resource for Physiology and Pharmacology at Stanford University