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    Using Bispectral Index™ Monitoring to Reduce Risk of Anesthestic Awareness

    By Jennifer Decker Arevalo, MA, contributor - 

    The movie Awake, a fictional psychological thriller about a man undergoing heart surgery while experiencing anesthetic awareness, is bringing public attention to the sedation-assessment conundrum that anesthesiologists and certified registered nurse anesthetists (CRNA) face every day: how to avoid over- or under-sedating patients, while at the same time being able to comprehend their neurologic status.

    “Awareness under anesthesia has been our profession’s ‘dirty little secret’ that we have long known about and tried to ‘sweep under the carpet’ with denial,” said Barry Friedberg, M.D., AMC, author of  A nesthesia in Cosmetic Surgery. “Hopefully, publicity about the issue may stimulate some to reevaluate all of the supportive evidence regarding the benefits of giving patients just the right amount of anesthesia that they need.”

    Friedberg believes that, much like Goldilocks of fairy-tale fame who searches to find the bowl of porridge that is not “too hot” or “too cold,” but “just right,” patients need to receive anesthesia that is not over- or under-dosed, but “just right.”

    Patient awareness under general anesthesia is a rare condition, affecting 0.1-0.2 percent of all surgical patients; however, the incidence of awareness may increase in certain clinical situations involving specific types of surgery, patients and anesthesia techniques.

    According to the American Association of Nurse Anesthetists (AANA), anesthetic awareness occurs when surgical patients can recall their surroundings or an event—sometimes even pressure or pain—related to their surgery while they are under general anesthesia. About 50 percent of patients may feel some degree of mental distress during or following anesthetic awareness; patients may also have intrusive thoughts and nightmares or develop post-traumatic stress disorder.

    Traditionally, anesthesiologists and CRNAs have relied on two intraoperative modalities to determine the depth of anesthesia: 1) Clinical techniques, such as checking for purposeful or reflex movement, especially since neuromuscular blocking drugs may mask this movement, and 2) Conventional monitoring systems, such as electrocardiogram, blood pressure, heart rate, end-tidal anesthetic analyzer and capnography.

    However, a third option known as brain function monitoring is also available. The Bispectral Index Monitor (BIS), developed by Aspect Medical System, Inc., is one of about six different types of brain function monitors currently available. It was approved by the Federal Drug Administration (FDA) in 1996 and is intended to measure patient response to the administration of potent sedative agents and decrease the risk of intraoperative awareness by providing the anesthetist with a quantitative assessment regarding the hypnotic state of the patient.

    The BIS is a cerebral monitor that uses a complex computer algorithm to assign a numerical value between zero and 100 to the probability of consciousness. According to the manufacturer, the BIS index range and clinical states of consciousness are: 100 - Awake; 80 - Light to Moderate Sedation; 60 - General Anesthesia; 40 - Deep Hypnotic State; 20 - Burst Suppression and 0 - Flat Line EEG.

    “Recall rarely occurs at BIS below 75,” said Dr. Friedberg. “’Overdosed’ is indicated when BIS readings are less than 45. Unfortunately for the patient, anesthesia at BIS below 45 is remarkably commonplace. The consequences of overdosing, like postoperative cognitive dysfunction (POCD) and coma, may be just as sinister as anesthetic awareness from under-dosing.”

    “Research has shown that routinely overdosing patients for fear of under-dosing increases the morbidity and mortality of unnecessarily deep anesthesia. Obviously, one cannot avoid this without using the technology to measure hypnotic depth in the first place.”

    For the past 10 years, Friedberg has been using BIS technology in combination with propofol ketamine monitored anesthesia care (PK MAC) as his routine, standard-of-care treatment for patients undergoing elective cosmetic surgery to reduce the risk for anesthetic awareness.

    “This technique is designed to maximize patient safety by minimizing the degree to which patients need to be medicated to achieve the illusion of general anesthesia, thus transforming it into ‘minimally invasive anesthesia’ (MIA)®,” said Dr. Friedberg.

    According to Friedberg, “MIA occurs following an incremental propofol induction to BIS less than 75 prior to the administration of the 50 mg dissociative dose of ketamine and the maintenance of the level of hypnosis to BIS 60 to 75.”

    “MIA enables me to educate surgeons about the need for additional local analgesia during a case,” continued Friedberg. “When a patient moves with a vasoconstricted field, the surgeon used to say that the patient was ‘too light.’ Now, being able to demonstrate BIS 60 to 75 (i.e. adequate propofol effect) with patient movement has eliminated the argument of ‘too light’ in favor of ‘more local.’ The patient ‘wins,’ as does the surgeon.”

    By using the BIS monitor, Friedberg is able to “improve propofol dosing accuracy, save 20 percent of unnecessary medication and still achieve the same effect as general anesthesia (patients do not hear, feel or remember their surgery), thus saving many dollars in wasted anesthetic.” MIA also results in maintenance of laryngeal reflexes, less respiratory depression and risk, improved safety and speedier recovery.

    “Furthermore, being able to measure BIS at 75 or less prior to injecting the ketamine provides a numerical basis to eliminate the negative side effects of ketamine while providing reproducible preemptive, non-opioid analgesia. Totally eliminating opioids for the past decade has enabled me to achieve an unprecedented 0.5% post-operative nausea and vomiting (PONV) rate in a high risk patient population without the use of anti-emetics.” 

    Although Friedberg’s published data, along with 2,800 published articles and abstracts (according to the manufacturer) support that BIS is an objective measure of sedation depth in general anesthesia, currently only 55 percent of all operating rooms in the U.S. have adopted BIS.

    Brain function monitoring is not considered by the American Society of Anesthesiologists (ASA), as an established means by which to prevent unintended intraoperative awareness and not routinely indicated for patients undergoing general anesthesia, thus resulting in reluctance by some anesthesiologists to use it.

    “The ones who remain reluctant to use BIS tend to be resistant to any change, believing that their way, which is based on ‘instinct,’ that is, trends in heart rate and blood pressure, is adequate in most cases,” said Friedberg. “Trends in vital signs are notoriously unreliable for this purpose.”

    On the other hand, i n its  Position Statement 2.12,  Unintended Awareness under General Anesthesia,  the AANA states that, if available, b rain function monitoring¾as an adjunct to other patient monitoring modalities¾should be considered, particularly in situations where the risk of intraoperative awareness is increased.

    Although the use of brain function monitoring is not officially part of any standard of care or practice guidelines, the AANA recommends that every anesthetizing location have a well-defined written policy for the prevention and management of anesthetic awareness. Additionally, in 2005 the AANA developed Considerations for Policy Development: Unintended Intraoperative Awareness, in conjunction with the Joint Commission’s 2004 Sentinel Event Alert No. 32, Preventing, and Managing the Impact of, Anesthesia Awareness to provide guidance for policy development.

    “It’s important to emphasize that the many anesthesiologists and CRNAs who have incorporated BIS monitoring into their practice have improved the care of their patients,” said Friedberg.

     

    Find more information about BIS on the manufacturer’s Web site:    Aspect Medical Systems 

    References:

    Friedberg BL: Propofol-ketamine technique: dissociative anesthesia for office surgery (a 5-year review of 1264 cases). Aesthetic Plast Surg.  1999 Jan-Feb;23(1):70-5.

    BIS Adoption Quick Facts. Aspect Medical System, Inc. Retrieved January 7, 2008 from http://www.aspectmedical.com/products/bis_quick_facts_popup.mspx



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