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Thread: Anesthesia awareness

  1. #1
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    Lightbulb Anesthesia awareness

    Anesthesia awareness, or "unintended intra-operative awareness" occurs during general anesthesia, when a patient has not had enough general anesthetic or analgesic to prevent consciousness and the recall of events.

    For patients undergoing general anesthesia, very few experience an anesthetic that is inadequate to keep them unconscious during an operation. In rare instances, the anesthetic may be inadequate resulting in awareness. In this situation,which is very rare, a 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. If anesthesia awareness does occur it is more common for the patient to be aware but do not feel pain or other unpleasant sensations.

    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 of difficulty in breathing.

    The experiences of patients with anesthesia awareness vary widely, and patient responses and sequelae vary widely as well. This experience may be extremely traumatic for the patient.

    Similar situations
    Patients who have conscious sedation and/or regional anesthesia (such as spinal or epidural anesthesia), are expected to have some recall, and are not considered to have experienced anesthesia awareness. These patients are awake enough to indicate to the anesthetist if they feel pain during the operation. Many patients remember fragments of conversation they heard as they were drifting off into general anesthesia, while they were waking up, or while they were recovering in PACU (post anesthesia care unit). These patients do not recall pain or unpleasant stimuli of the surgery, but may be frightened by the belief that they were "awake" during the operation.

    In some cases, post traumatic stress disorder (PTSD) may arise after intraoperative awareness, causing the patient to require counseling for an extended period.

    Patients who experience full awareness with explicit recall may have suffered an enormous trauma. Some patients experience posttraumatic stress disorder (PTSD), leading to long-lasting after-effects such as nightmares, night terrors, flashbacks, insomnia, and in some cases even suicide.There is evidence that early psychological counselling and support can reduce the amount of harm and chances of developing PTSD.The patient must be treated sympathetically and with compassion.

    Prompt inspection of the anesthesia equipment and record is important and may help prevent future occurrences. It is also important that a case of suspected awareness be communicated to the patient's healthcare team, and that the event be scrutinised closely by senior anesthetic medical staff.

    Risk factors/Causes

    Paralytics/muscle relaxant use
    The most common risk factor is the use of a paralytic/muscle relaxant. Under general anesthesia it is common for the patient's muscles to be paralysed (with a neuromuscular blocking drug) in order to allow the surgeon safe access to the body cavities (e.g. abdomen, thorax or cranium), or to ensure the patient tolerates mechanical ventilation, or to keep the patient absolutely still for microsurgery, e.g. on the eye. The paralytic agent does not affect consciousness, or the ability to feel pain, at all. A fully paralyzed patient is unable to move, to speak, to blink the eyes, or otherwise respond to the pain. Muscle paralysis does not typically interfere with the functioning of the autonomic nervous system. This may result in signs such as an increased heart rate (tachycardia) and blood pressure (hypertension), as well as dilation of the pupils (mydriasis), sweating (diaphoresis), and the formation of tears (lacrimation) in response to pain. Therefore, even though the patient may not be able to directly signal their distress, they may exhibit signs of awareness which may be detectable by clinical vigilance.

    Many types of surgery do not require the patient to be paralysed. A patient who is anesthetised, but not paralysed, is likely to move in response to a painful stimulus if the anesthetic is inadequate for any reason. This can happen without conscious perception or memory of the painful stimulus. Therefore, anesthetic awareness is uncommon in patients who have not been paralysed.

    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." 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 patients.

    Improper equipment maintenance/anesthetist error
    Human errors include inadequate drug dose, inadequate monitoring, and failure to refill the anesthetic machine's vaporisers with volatile anesthetic. Other causes of awareness include unfamiliarity with techniques used, e.g. intravenous anesthetic regimes, or inexperience. Poor anesthetic technique is a combination of any of the above, but also includes techniques which 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. This may be caused by an empty vaporizer (or nitrous oxide cylinder) or a malfunctioning intravenous pump or disconnection of its delivery tubing. Problems with flowmeters or monitors may also contribute to risk of awareness.

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

    Patient physiology
    Possible 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. Younger age, 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. Anxiety prior to the surgery can increase the amount of anesthesia required to prevent recall.

    The risk of awareness is reduced by simple steps and good clinical practice: well-trained personnel; careful checking of drugs, doses and equipment; good monitoring, and careful vigilance during the case.

    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 anaesthetised (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 anaesthesia is usually signified by a number between 60 and 40 (this varies with the specific system used). These newer technologies include the bispectral index (BIS),EEG entropy monitoring, auditory evoked potentials, and several other systems.
    The most recent technological advancement in awareness monitors is the SNAP II. The SNAP II monitor is the only monitor to evaluate high and low frequency EEG in real time to create an objective metric SNAP Index, which helps measure the state of the brain and assess the level of consciousness. The SNAP monitor captures the most useful information in low-frequency EEG and utilizes high-frequency component in return to consciousness

    Studies have shown that a low frequency band in the 1-15Hz range of 0.40 indicates declining alertness while high frequency range between 201-500Hz can be a marker of cognitive function and or capacity which the SNAP utilizes in return to consciousness. The SNAP monitor also minimizes the bands that are most heavily contaminated by Electromyography (EMG), which causes interference in other monitors.
    A study done by the British Journal of Anesthesia in June 2006,stated, the SNAP index 1 min before awakening had returned to or exceeded the baseline awake value in 64% of the subjects, and in 90% of the subjects at awakening. The corresponding percentages for the BIS were 8% at both times. Therefore the SNAP II may have an advantage compared with the BIS in predicting imminent awakening when compared with the awake baseline values. The faster return to baseline found with the SNAP device may be a result of the inclusion of the high-frequency EEG component in the Calculation of the index, as frequencies as high as 128Hz have shown a high prediction probability for separation of awareness and unresponsiveness .

    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 diathermy). This means that the technology does not yet exist which will reliably monitor depth of anaesthesia for every patient and every anaesthetic.

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

    Currently, the anesthesia provider community accepts that anesthesia awareness occurs, however there is not much of a consensus on the incidence or on how often patients experience long term mental distress. A study from Sweden in 2002 attempted to follow up 18 patients approximately 2 years after previously diagnosed 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 complained about 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.

  2. #2
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    Lightbulb Anesthesia awareness (Contd...)

    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 which of the following words were played to you during your surgery. As a further example please note the following scenario. 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 being directly asked. 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.

    Awake craniotomy
    Under very unusual circumstances, neurosurgeons may wish to wake a patient during an operation in order to test the function of specific parts of their brain while they are awake. This procedure is called an awake craniotomy.
    Under very unusual circumstances, neurosurgeons may wish to wake a patient during an operation in order to test the function of specific parts of their brain while they are awake. This procedure is called an awake craniotomy.

  3. #3
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    Lightbulb Awake During Surgery: How Rare?

    Less Than 1% of Patients Experience Anesthesia Awareness Under General Anesthesia

    Doctors addressed the topic in a live webcast from New York, spurred by Friday's release of the movie Awake, a fictional thriller based on anesthesia awareness, also called unintended intraoperative awareness.

    There have been "a lot of different studies" trying to pinpoint the incidence of anesthesia awareness, Marc Bloom, MD, PhD, of New York University Medical Center, told reporters.

    Several studies put the incidence of anesthesia awareness at 0.1% of all general anesthesia patients. That works out to be about 21,000 of the 21 million people in the U.S. who get general anesthesia in a typical year.

    But if high-risk patients aren't included, the numbers drop to about one in 40,000 patients, Bloom says.

    "But let's get out of this box of how often it occurs. Really, one case is too many," says Orin Guidry, MD, of the Medical University of South Carolina.

    "As anesthesiologists, we are not going to stop until we can get that risk down to zero," says Guidry, who is a past president of the American Society of Anesthesiologists (ASA).

    (Do you have a fear of waking during surgery? Share your stories on the Health Cafe message board.)

    Avoiding Anesthesia Awareness

    Anesthesia experts urge patients and doctors to talk about anesthesia before surgery, including a frank discussion about side effects, risks, and past experiences with anesthesia.

    Some patients -- including people getting heart surgery, emergency surgery, or C-sections -- may be more likely to experience anesthesia awareness. That's because doctors may need to use a lighter dose of anesthetic to keep the patient (or baby, in the case of C-section) stable.

    Patients may remember procedures that involve local anesthesia, but that's not anesthesia awareness, the panelists note.

    The use of brain function monitors during surgery can cut the chance of a patient experiencing anesthesia awareness, according to Bloom, Guidry, and colleagues.

    But the doctors warn that those devices don't rule out all possibility of anesthesia awareness.

    They describe a fine line between too little anesthesia, which may lead to anesthesia awareness, and too much anesthesia, which may cause side effects including nausea and vomiting after surgery.

    "We are still in a situation where we have to use all of our senses and all of our knowledge," Bloom says. "At this point, there is no way to flip a switch and let the monitor tell us how much [anesthesia] to give."

    The webcast was sponsored by Stryker, which makes a brain function monitor.

    Anesthesia Awareness Advocate

    All of the doctors who took part in the webcast say they don't know of any of their patients who experienced anesthesia awareness.

    But Carol Weihrer, who experienced anesthesia awareness when she was having surgery to remove an eye, says that posttraumatic stress disorder (PTSD) is frequently reported by the thousands of anesthesia awareness patients she's talked to over the years.

    Weihrer explains that during her surgery, she got an initial dose of anesthesia but further anesthesia wasn't immediately available because, as she says, "my anesthesiologist hadn't checked his equipment."

    "My brain was as alert as it was right now," says Weihrer, calling the experience "very traumatizing." Weihrer is the president and founder of Anesthesia Awareness Campaign Inc.

    Guidry, who wasn't involved in that operation, notes that Weihrer's situation may have happened because her anesthesia wore off, not because it didn't work.

    Handling Anesthesia Awareness

    Tom McKibben, CRNA, past president of the American Association of Nurse Anesthetists, recommends that patients be asked these questions as they recover from procedures involving general anesthesia:

    * What is the last thing you remember before surgery?
    * What is the first thing you remember after surgery?
    * Do you remember anything during the procedure?
    * Did you dream during the procedure?

    He adds that in the first few weeks after general anesthesia, patients should also be asked what the worst thing was about the operation.

    "If they say the nightmares or recurring dreams [or other disturbing experiences apart from postsurgery pain] we need to follow up with that," says McKibben.

    That follow-up may include referrals for counseling to help patients cope with what Weihrer calls the "life-changing experience" of anesthesia awareness.

  4. #4
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    So does this phenomenon occur because the pt wasnt administered adequate amount of anaesthesia? is that substantiated with some evidence?
    Last edited by mgt9; 12-14-2007 at 06:34 PM.

  5. #5
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    Default Yes it is...But concept is little bit different

    Anaesthesia awareness is due to adequate amount of anaesthesia administered..As per experts anaesthesia administered is not too low or too high to produce side effects like vomiting or nausea..There may not be awareness if some high amount is given but it'll lead to side effects...This is the problem..

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