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Study Evaluating Ways of Preventing Patients From Being Awake During High-Risk Surgery and Anesthesia

This study has been completed.
Barnes-Jewish Hospital
Information provided by (Responsible Party):
Michael Avidan, Washington University School of Medicine Identifier:
First received: January 20, 2006
Last updated: July 20, 2012
Last verified: July 2012
The overall purpose of this study is to see if a Bispectral Index (BIS) monitor, a Food and Drug Administration (FDA) approved brain monitoring device, will help to reduce the risk of patients remembering being awake during surgery. The BIS monitor may be able measure how asleep a patient is during surgery. Using the BIS monitor to guide anesthesia will be compared with using the concentration of anesthetic gas to guide anesthesia.

Condition Intervention Phase
Explicit Recall of Intra-operative Events
Device: BIS Monitor guided algorithm
Behavioral: Volatile anesthetic guided algorithm
Phase 2
Phase 3

Study Type: Interventional
Study Design: Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Double Blind (Participant, Outcomes Assessor)
Primary Purpose: Prevention
Official Title: B-Unaware Study: Comparison of BIS-guided Anesthesia With End-Tidal Volatile-Guided Anesthesia to Decrease The Incidence of Awareness During High-Risk Surgery

Resource links provided by NLM:

Further study details as provided by Washington University School of Medicine:

Primary Outcome Measures:
  • The incidence of explicit recall of events during the surgical and anesthetic periods. [ Time Frame: 30 days ]

Secondary Outcome Measures:
  • 1 Anesthetic concentrations & BIS values in each group. [ Time Frame: 1 day ]
  • 2 Implicit memory (number). [ Time Frame: 30 days ]
  • 3 Dreaming. [ Time Frame: 30 days ]
  • 4 One-year mortality (and "anesthetic depth"). [ Time Frame: 1 year ]
  • 5 Relation of assessment to BIS value. [ Time Frame: 30 days ]
  • 6 Relation of events (e.g. movement) to BIS & ETAG. [ Time Frame: 1 day ]
  • 7 Relation of EMG to BIS. [ Time Frame: 1 day ]

Enrollment: 2000
Study Start Date: August 2005
Primary Completion Date: October 2006 (Final data collection date for primary outcome measure)
Arms Assigned Interventions
Experimental: BIS Monitor guided algorithm
BIS guided algorithm (BIS target 40 to 60) during anesthesia. Alarms when BIS is outside this range.
Device: BIS Monitor guided algorithm
BIS guided algorithm (BIS target 40 to 60) during anesthesia. Alarms when BIS is outside this range.
Active Comparator: Volatile anesthetic guided algorithm
Volatile anesthetic guided algorithm. Target anesthetic concentration 0.7 to 1.3 minimum alveolar concentration during anesthesia. Alarms when anesthetic concentration not in this range.
Behavioral: Volatile anesthetic guided algorithm
Volatile anesthetic guided algorithm. Target anesthetic concentration 0.7 to 1.3 minimum alveolar concentration during anesthesia. Alarms when anesthetic concentration not in this range.

Detailed Description:

General anesthesia is a state of drug-induced unconsciousness, during which patients should neither perceive nor recall noxious stimuli. Many patients facing surgery dread the prospect of being awake, in pain and unable to move owing to inadequate general anesthesia. A large multi-center study in the USA showed that, despite modern anesthesia techniques, the overall incidence of awareness or conscious recall remains about 0.1-0.2%. For high-risk (for awareness) surgery, such as cardiac surgery, trauma surgery and obstetric surgery, the incidence of conscious recall approaches 1%. This can lead to extreme anxiety and even posttraumatic stress disorder. Several monitors, including the Bispectral Index (BIS), which is based on processed electroencephalographic information, have been developed in an attempt to monitor depth of anesthesia. A recent landmark study suggested that harnessing the information provided by the BIS monitor decreases the incidence of explicit recall during high-risk surgical procedures from almost 1% to 0.1%. The possible impact of this study is enormous. The American Society of Anesthesiologists and the American Association of Nurse Anesthetists do not currently consider neurological monitors an essential part of routine anesthesia care. Increasingly, members of the anesthetic community are suggesting that for every patient undergoing general anesthesia, especially for procedures where the risk of awareness is considered higher, a neurological monitor, such as the BIS monitor, should be routinely applied.

Explicit recall under general anesthesia is a major concern among members of the public and has even been featured on the popular Oprah Winfrey Show. Several patients presenting for surgery at Barnes Jewish Hospital have questioned whether the anesthesia provider would be using a BIS monitor to "prevent awareness". Excluding the cost of the BIS monitor itself, the cost to use BIS is $17.50 for the disposable strip. If this monitor was to be used for every anesthetic administered at Barnes Jewish Hospital, this might translate to an annual cost of about $500,000. Explicit recall, especially when patients have been aware and unable to move, is a serious complication that frequently precipitates posttraumatic stress disorder. If indeed the BIS monitor does decrease the incidence of explicit recall, this could translate into a cost effective and more importantly clinically imperative intervention. Currently BIS monitors, or similar alternatives, are not used routinely to monitor depth of general anesthesia at Barnes Jewish Hospital.

However, there are several concerns regarding the studies that have been conducted using the BIS monitor. There have been no parameters guiding administration of anesthesia in the control groups. BIS data have not been collected for patients in control groups, which prevents retrospective analysis and assessment of the true sensitivity, specificity, positive and negative predictive values of the BIS recordings. Most of the studies have been funded by the manufacturer of the device, which introduces a potential conflict of interest and investigator bias. In view of the current pressure to adopt BIS monitoring or an equivalent into the standard of anesthesia care, it is essential to conduct a study to address some of the concerns. The hypothesis of this proposed study is that an anesthetic algorithm can be designed for high-risk surgical patients such that the incidence of awareness will be equivalent to or lower than that in a group where anesthesia depth is guided by the BIS monitor.


Ages Eligible for Study:   18 Years and older   (Adult, Senior)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   No

Inclusion Criteria:


General Anesthesia with volatile anesthetic


Major Criteria (any 1 of the following:)

  1. Medications - anticonvulsants, abuse of opiates, benzodiazepines, cocaine
  2. EF<40%
  3. Prior history of awareness (recall)
  4. History of difficult intubation or anticipated difficult intubation
  5. ASA IV or V status
  6. Aortic stenosis
  7. End stage lung disease
  8. Marginal exercise tolerance not secondary to musculoskeletal dysfunction
  9. Pulmonary hypertension
  10. Daily alcohol consumption

Minor Criteria (any 2 of the following)

  1. Beta blockers
  2. COPD
  3. Moderate exercise tolerance not secondary to musculoskeletal dysfunction
  4. Smokes ≥2 packs per day
  5. Morbid obesity BMI>30 -

Exclusion Criteria:

  1. Surgical procedure that prevents the use of the BIS (e.g surgery of forehead)
  2. Patient positioning prevents use of the BIS
  3. Surgery with wake-up test.
  4. Less than 18 years of age
  5. Vulnerable populations, such as those with dementia and those unable to provide informed consent.
  6. Stroke with residual neurological deficits
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Please refer to this study by its identifier: NCT00281489

United States, Missouri
Barnes-Jewish Hospital
St Louis, Missouri, United States, 63110
Sponsors and Collaborators
Washington University School of Medicine
Barnes-Jewish Hospital
Principal Investigator: Michael S Avidan, MBBCh Washington University School of Medicine
Study Director: Beth Burnside Washington University School of Medicine
  More Information

Publications automatically indexed to this study by Identifier (NCT Number):
Responsible Party: Michael Avidan, Director, Institute of Quality Improvement, Research & Informatics, Washington University School of Medicine Identifier: NCT00281489     History of Changes
Other Study ID Numbers: 04-1112
Study First Received: January 20, 2006
Last Updated: July 20, 2012

Keywords provided by Washington University School of Medicine:
Explicit Recall

Additional relevant MeSH terms:
Central Nervous System Depressants
Physiological Effects of Drugs processed this record on May 23, 2017