AWARENESS DURING ANESTHESIA
| RESPONSIVENESS DURING SURGERY vs AWARENESS —Donald M. Mathews, MD, Associate Professor of
Anesthesiology, New York Medical College; Chief, Ambulatory Anesthesia Services, St. Vincent’s Hospital and
Medical Center, New York, NY
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| Awareness during surgery: causes—medically difficult situations resulting in delivery of inadequate amount of
hypnotic agent; unreliable technique for delivery of hypnotic agent, eg, nitrous narcotic technique; unappreciated
increased anesthetic requirements, eg, unrevealed chronic illicit substance abuse or benzodiazepine abuse; equipment
malfunction or lack of vigilance
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| Incidence of awareness: 1 to 2 per 1000 low-risk patients have ability to remember something about surgical procedure;
however, anesthesiologists’ perception does not equate to incidence
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 | Reasons for underreporting: patients who experience short auditory recall or transient awareness may not report it;
not all memory formation available to patients in immediate postoperative period; Sandin et al—Scandinavian
data; patients undergoing general anesthetic interviewed on day of surgery, day 1 to 3, and day 7 to 14 after anesthesia;
incidence of recall 1 to 2 per 1000; recall available to only 6 patients in immediate postoperative period;
most patients displayed recall during day 7 to 14
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| Spectrum of experience: 18% to 39% of cases of recall of awareness include element of pain; 36% to 92% of cases
involve experience of anxiety; some patients develop psychologic issues, ranging from mild and transient to prolonged
posttraumatic stress disorder (PTSD)
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| Utilization of responsiveness to ensure lack of consciousness: prediction probability (PK)—described in
1996 by Smith et al; evaluates change in anesthetic depth in relation to specified indicator; if anesthetic depth and
indicator in absolute correlation, PK=1; if no relationship, PK=0.5; data for comparison must be gathered from
same response to simulation test procedures and over same distribution of anesthetic depth
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| Autonomic nervous system (ANS): not 100% accurate as measure of states of consciousness; Domino et al—
analyzed data from Closed Claims Database; “classic signs of hypertension and tachycardia absent during most
cases of recall during general anesthesia”; Russell et al (2001)—“virtually all original clinical signs described
by Snow and developed by Geudel rely on muscle activity: cardiovascular signs are not mentioned. The origins
of using cardiovascular indices to gauge depth of anesthesia are unclear and we are not aware of any study
which has shown them to be of value in detecting consciousness”
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| Predictive value of ANS: study outcomes—mean arterial blood pressure (BP) appears to be relatively good correlate
to state of consciousness; heart rate poor correlate; no data on predictive value of ANS in elderly or sick patients
or patients taking vasoactive medications
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| Patient movement: no data on predictive value of movement in determining likelihood of intraoperative consciousness
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| Muscle relaxants: Closed Claims Database shows muscle relaxants associated with >2-fold increased risk for awareness;
patients trying to communicate with caregiver by moving often receive dose of muscle relaxant in response
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| Response to stimulation: animal studies show most movement reflexively mediated through spinal cord and does
not involve cerebral cortex; most patient movement in operating room likely mediated by spinal reflexes;
speaker believes impossible to determine whether patient movement due to spinal reflexes or attempt at communication;
however, regardless of etiology, movement represents inadequate anesthetic state
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| Treatment: movement should never be treated with muscle relaxants alone; need something to augment inadequate
anesthetic state
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| Lack of movement: in studies (eg, isolated forearm studies), not shown to guarantee lack of consciousness; response
to command important means of detecting awareness but may not detect all instances of wakefulness
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| Brain function monitoring: monitors exploit measurable changes in electroencephalography readings elicited
when patients transition from awake to isoelectric state after administration of γ-aminobutyric acid (GABA) agonists;
monitors convert brain activity into reading from 0 to 100 that provides insight into level of consciousness
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| Prediction of consciousness: studies show monitors good at detecting change in depth of anesthesia, and recent report
showed bispectral index (BIS) and cerebral state index (CSI) monitors significantly better than mean arterial
BP; monitors correlate with level of consciousness well in simple models, but less effective with complex data
sets; in all studies, brain activity monitors outperform heart rate and BP
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| Concerns: accuracy and artifacts; cost
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| Prevention of awareness: BIS monitoring to prevent awareness during anesthesia (B-Aware) study—high-risk patients
interviewed after undergoing general anesthesia; in group not receiving BIS monitoring, incidence of awareness
≈1%; in group receiving BIS monitoring, statistically significant decrease in awareness (2 cases, 1 occurred
during intubation and 1 occurred during surgery when BIS monitor reading 55-59); Scandinavian study—
incidence of awareness in patients not receiving BIS monitoring ≈0.16%; in group receiving BIS monitoring, statistically
significant 80% decrease in incidence (2 cases in 5000 patients, both occurring during induction and intubation)
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| AWARENESS DURING ANESTHESIA —Stanley D. Brauer, MD, Professor of Anesthesiology, Director of Cardiac
Anesthesia, Loma Linda University School of Medicine, Loma Linda, CA
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| Delayed recall experiences: case of 58-yr-old psychologist who underwent heart surgery at 14 yr of age; patient
did not experience recall until adulthood, when trigger prompted recall of surgical experience
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| Consumer awareness of anesthetic awareness: many newspapers covered Joint Commission on Accreditation of
Healthcare Organizations (JCAHO) Sentinel Event Alert on anesthesia awareness; much information available on internet
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| Experience of awareness: many patients report chilling experiences; many patients unwilling to report experience;
PTSD may develop; medications may hide awareness
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| JCAHO Sentinel Event Alert: incidence—0.1% to 0.2%, indicating potential for >20,000 cases/yr in United
States; symptoms—most commonly auditory recollections; perception of inability to breathe; less commonly pain;
high-risk surgery—cardiac; major trauma; obstetric; additional risk factors—female sex; muscle relaxants; intravenous
anesthetics; history of drug tolerance
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| Food and Drug Administration (FDA) statement on brain function monitoring: “devices may have role
in preventing and detecting anesthesia awareness in patients with highest risk”; conflicts with JCAHO recommendation
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| Definitions: anesthesia—rendering patient unconscious and not perceiving pain; recall—conscious or explicit
memory of event that may be painful; wakefulness—patient responding to verbal stimuli during surgery; implicit
memory—changes in behavior produced by previous experiences that do not require conscious recollection of experiences;
perceptual priming—no change in behavior, but word fragments may be preserved when later presented
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| Physiologic response to awareness under anesthesia: movement, lacrimation, sweating, tachycardia, hypertension,
and hyperventilation all potential clues but not reliable; use of narcotic agents and muscle relaxants in current
anesthesia techniques can mask signs of inadequate anesthesia; concurrent medications can block physiologic
signs
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| Memory activation: occurs with all current techniques; more likely to occur with opiate-based anesthetics and
lighter anesthetic levels; data suggest BIS monitor range of 40 to 60 may block memory activation
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| Problems with deep anesthesia: study—appeared to be higher incidence of mortality in patients with relatively
low intraoperative BIS level
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| Incidence of awareness: Sebel et al (2004)—largest prospective study; ≈20,000 patients from 7 academic centers; incidence
of recall ≈0.13%; key associated factor sicker American Society of Anesthesiologists (ASA) status; age and sex
had no impact; >6% of patients reported intraoperative dreaming (most recollections vague and not unpleasant); British
study—interviewed patients in postanesthesia care unit (PACU), 1 to 3 days and 1 to 2 wk postoperatively; 39% of recall
incidents identified in PACU; >25% identified 1 to 2 wk postoperatively; muscle relaxants associated with 2-fold increased
risk; authors concluded that after analyzing recall incidents, monitoring end-tidal anesthetic gas concentrations or
more frequent use of benzodiazepines would not reduce recall or awareness incidences
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| JCAHO summary recommendations: educate staff; be aware of at-risk patients; ensure institution has all appropriate
monitoring devices; ensure procedure in place to provide postoperative counseling for PTSD
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| Management of patient with awareness: interview patient after procedure, detailing patient’s experience; sympathize
and apologize to patient; ensure patient that experience real; provide explanation and answer questions; refer
to risk management or quality improvement departments; make surgeon aware
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| Reducing risk for awareness: premedication with amnestic drugs may be helpful with light anesthesia; consider
higher doses of induction agents in certain situations; avoid paralysis; ensure vaporizers and other equipment in full
working order
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| Malpractice issues: anesthesia provider primarily responsible; most cases brought by patients with distinct and unpleasant
recall successful; typically, cases settled out of court; awareness settlements account for 2% of Closed Claims
Database
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| Brain function monitors: difficult to know which monitor best; appear to have similar results in most clinical situations;
all devices generate anesthesia-depth number (roughly comparable to each other)
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| BIS monitor: produced by Aspect Medical Systems; touted as new vital sign; estimated to have 90% market share
(though likely less due to competition; 7 devices now available); disposable sensors relatively affordable; boosted by
FDA statement
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| Limitations of brain function monitors: may interfere with electrocautery and electrical devices (most studies of
awareness cite this as key problem); muscle activity can be significant problem; limited data on use in pediatric
patients; nitrous oxide can distort values on BIS monitor; ketamine reported to artificially raise BIS monitor reading
due to pharmacologic effect on brain; etomidate may raise BIS monitor reading through skeletal muscle activity;
halothane may raise BIS monitor reading, compared to other inhalation agents
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| Critics: case reports of patients not being adequately anesthetized despite adequate BIS monitor reading
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| ASA practice advisory: provides most up-to-date information available but does not represent standard or guideline;
“decision to use brain function monitor should be made on case-by-case basis by individual practitioner for
selected patients”
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| Myles et al (2004): published in Lancet; patients 18 yr of age in whom use of muscle relaxant predicted; patients had
1 risk factor for recall, ie, cesarean section, cardiac surgery, acute trauma surgery, history of awareness, difficult intubation,
anticipated rigid bronchoscopy, drug tolerance, or hemodynamic impairment; 2643 patients randomized to
receive BIS monitoring or not; anesthetic technique left to practitioner; blinded observers interviewed patients at 4
hr, 30 hr, and 30 days; blinded independent committee assessed reports and decided which cases constituted awareness;
2 patients in BIS-monitor group and 11 in routine-care group experienced awareness (statistically significant
result); cardiothoracic procedures associated with increased risk; authors concluded BIS monitor warranted for any
patient at increased risk for recall, such as surgeries needing muscle relaxants; potential limitations—anesthetic
techniques not standardized; Hawthorne effect, ie, initiation of study changes behavior; speaker’s conclusion—
basic study design well done, and results support authors’ conclusion that brain function monitoring should be performed
in high-risk patients
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| Ekman et al: 2 hospitals collaborated over 17-mo period; 5000 consecutive patients received BIS monitoring, then
compared to historical controls in recent time frame from same institutions; all patients required muscle relaxants
and/or intubation; targeted BIS monitor range 40 to 60; standard interview techniques performed but not by
blinded observers; BIS monitoring associated with significant reduction in awareness; 2 cases of recall involving
17-yr-old woman with recall of prolonged nasal intubation attempts and 22-yr-old patient with recall of endotracheal
tube placement; authors tout result as lowest reported awareness rate in literature when muscle relaxants
used; potential limitations—anesthetic technique; Hawthorne effect; demographics; nonblinded interviews;
nonrandomized trial; historical controls
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Educational Objectives
| The goal of this activity is to educate the listener about awareness during anesthesia. After hearing and assimilating
this program, the clinician will be better able to:
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| 1. Identify patients at high risk for awareness during anesthesia.
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| 2. Prevent awareness during anesthesia.
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| 3. Conduct postoperative follow-up to identify cases of awareness during anesthesia.
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| 4. Discuss the role of brain function monitoring in contemporary anesthesia practice.
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| 5. Utilize brain functioning monitors in the prevention of awareness during anesthesia.
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Suggested Reading
Bevacqua BK, Kazdan D: Is more information better? Intraoperative recall with a Bispectral Index monitor in
place. Anesthesiology 99:507, 2003; Bouillon TW et al: Pharmacodynamic interaction between propofol and
remifentanil regarding hypnosis, tolerance of laryngoscopy, bispectral index, and electroencephalographic approximate
entropy. Anesthesiology 100:1353, 2004; Dahaba AA: Different conditions that could result in the bispectral
index indicating an incorrect hypnotic state. Anesth Analg 101:765, 2005; Ekman A et al: Reduction in the incidence
of awareness using BIS monitoring. Acta Anaesthesiol Scand 48:20, 2004; Hellwagner K et al: Recollection
of dreams after short general anaesthesia: influence on patient anxiety and satisfaction. Eur J Anaesthesiol 20:282,
2003; Iselin-Chaves IA et al: Investigation of implicit memory during isoflurane anesthesia for elective surgery
using the process dissociation procedure. Anesthesiology 103:925, 2005; Kakinohana M et al: Emergence from
propofol anesthesia in a nonagenarian at a Bispectral Index of 52. Anesth Analg 101:169, 2005; Kalkman CJ,
Drummond JC: Monitors of depth of anesthesia, quo vadis? Anesthesiology 96:784, 2002; Kerssens C et al: No
evidence of memory function during anesthesia with propofol or isoflurane with close control of hypnotic state. Anesthesiology
102:57, 2005; Kerssens C et al: Awareness: Monitoring versus remembering what happened. Anesthesiology
99:570, 2003; Lennmarken C et al: Victims of awareness. Acta Anaesthesiol Scand 46:229, 2002;
Luginbuhl M, Schnider TW: Detection of awareness with the bispectral index: two case reports. Anesthesiology
96:241, 2002; Myles PS et al: Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware
randomised controlled trial. Lancet 363:1757, 2004; Rampersad SE, Mulroy MF: A case of awareness despite
an "adequate depth of anesthesia" as indicated by a Bispectral Index monitor. Anesth Analg 100:1363, 2005;
Schmidt GN et al: Comparative evaluation of the Datex-Ohmeda S/5 Entropy Module and the Bispectral Index
monitor during propofol-remifentanil anesthesia. Anesthesiology 101:1283, 2004.
Faculty Disclosure
In adherence to ACCME guidelines, the Audio-Digest Foundation requests all lecturers to disclose any significant financial
relationship with the manufacturer or provider of any commercial product or service discussed. For this issue,
the following has been disclosed: Dr. Brauer is a consultant for Bayer.
Dr. Mathews spoke at the Postgraduate Assembly in Anesthesiology, presented December 9-13, 2005, in New York,
NY, by the New York State Society of Anesthesiologists. Dr. Brauer spoke at Advances in Clinical Anesthetic Practice:
34th Annual Symposium, presented February 18-22, 2006, in Rancho Mirage, CA, by the Loma Linda University
School of Medicine, Department of Anesthesiology. The Audio-Digest Foundation thanks the speakers and the
sponsors for their cooperation in the production of this program.
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