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Bispectral Index (BIS) Versus Electronic Alerts in the Prevention of Anesthesia Awareness: the Michigan Awareness Control Study (MACS)

The safety and scientific validity of this study is the responsibility of the study sponsor and investigators. Listing a study does not mean it has been evaluated by the U.S. Federal Government. Read our disclaimer for details. Identifier: NCT00689091
Recruitment Status : Completed
First Posted : June 3, 2008
Results First Posted : November 17, 2014
Last Update Posted : December 7, 2017
Foundation for Anesthesia Education and Research
American Society of Anesthesiologists
Washington University School of Medicine
University of Chicago
University of Manitoba
Information provided by (Responsible Party):
George Mashour, University of Michigan

Brief Summary:
Awareness during anesthesia is a problem receiving increased attention by patients, clinicians, and the general public. The incidence of intraoperative awareness has been reported to be between 1-2/1000 cases, but recent data suggest that this may be an overestimate. The Bispectral Index (BIS) Monitor is an electroencephalographic method of assessing depth of anesthesia that has been shown in one study to reduce the incidence of awareness during anesthesia in the high-risk population (Myles et al, 2004). In the study of Myles et al, the number needed to treat (NNT) in order to prevent one case of awareness in the high-risk population was 138, with an associated cost of approximately US$2200. Since the NNT and the associated cost of treatment would be much higher in the general population, the efficacy of the BIS monitor in preventing awareness in all anesthetized patients needs to be clearly established. Furthermore, recent data suggest that the BIS may not be useful in the high-risk population. The investigators propose a prospective, randomized, controlled trial comparing the BIS monitor to electronic alerts based on non-electroencephalographic gauges of anesthetic depth.

Condition or disease Intervention/treatment Phase
Awareness During General Anesthesia Device: Bispectral Index Monitor Device: Electronic MAC alert Not Applicable

Detailed Description:

Electronic alerts have been developed and employed at our institution and have been shown to increase compliance with both clinical and administrative tasks (O'Reilly et al, 2006; Kheterpal et al, 2007). The investigators have developed electronic alerts for the purpose of informing the clinician of potentially insufficient anesthesia based on minimum alveolar concentration (MAC). The algorithm is as follows:

  • Every 5 minutes the alerting system checks every active case in our operating rooms. It takes approximately 1 second for this scan of all active cases to occur.
  • Conditions for an "active case" are:

    1. data capture is possible (i.e., not a paper record)
    2. data capture is active (i.e., "patient in room" has been electronically entered and end-tidal [Et] CO2 is detected)
    3. case has been identified as a general anesthetic
    4. "anesthesia induction end" has already been documented
    5. request for recovery room bed or transport to an intensive care unit has not been documented
    6. surgical dressing completion has not been documented
  • The alerting system checks the most recent value (within a specified time period) of:

    1. Et Sevoflurane (MAC=2.0)
    2. Et Isoflurane (MAC=1.2)
    3. Et Desflurane (MAC=6)
    4. Et Nitrous Oxide (MAC=105) and compares it to the MAC of each agent. It adds the resulting MAC values together for "current total MAC."
  • The system then checks for a charted propofol infusion in mcg/kg/min and divides by 150, assuming that 150 mcg/kg/min is "1.0 MAC" for propofol. The analogous concept of MAC for propofol is "Cp50"- the plasma or blood concentrations at which 50% of patients do not move in response to a noxious stimulus. Since the investigators do not have the technology at our institution to calculate Cp50 or Cp50-awake, the investigators have chosen the above propofol dose as an initial value based on clinical experience. The resultant MAC equivalent is added to current total MAC.
  • The system next checks for a dexmedetomidine infusion with a rate of 0.2 mcg/kg/hour or greater. If present, it multiplies the current total inhalational MAC by 2, as dexmedetomidine can reduce MAC by 50%.
  • At this point, the "current total MAC" is defined as: Et Sevo /2 + Et Iso /1.2 + Et Des/6 + Et Nitrous /105 + propofol rate (in mcg/kg/min)/150. If dexmedetomidine is >0.2 mcg/kg/hour, inhalational MAC is multiplied by 2.
  • If this total mac < 0.50, it checks to see if a bolus of propofol, midazolam, etomidate, or thiopental has been given in the preceding 10 minutes.
  • It alerts the clinician signed into the case within 30-60 seconds if total age-adjusted MAC < 0.50 AND no bolus has been documented in the last 10 minutes.

This will be the protocol in the MAC-guided group. In the BIS-guided group an electronic alert will be sent if the BIS value is >60. If an alert is triggered, the clinician electronically signed into the case receives an alphanumeric page stating "Potentially insufficient anesthesia, please check vaporizers and intravenous lines."

The investigators are collaborating with Washington University, the University of Chicago, and the University of Mannitoba, who will also be testing a MAC-based protocol in comparison to the BIS.

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Study Type : Interventional  (Clinical Trial)
Actual Enrollment : 22185 participants
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Double (Participant, Investigator)
Primary Purpose: Prevention
Official Title: A Prospective, Randomized, Controlled Trial Comparing Bispectral Index Monitoring to Electronic Alerts for Prevention of Awareness During Anesthesia in the General Population
Study Start Date : May 2008
Actual Primary Completion Date : April 2010
Actual Study Completion Date : June 2010

Arm Intervention/treatment
Experimental: BIS group
This group will have BIS values visible and will receive alerts when the value is >60.
Device: Bispectral Index Monitor
Comparison of two different alerting protocols. One using the bispectral index monitor and one using the MAC alerting protocols.

Active Comparator: MAC Alert
This group will receive an alert if total MAC (including intravenous infusions) is <0.5 age-adjusted.
Device: Electronic MAC alert
Comparison of two different alerting protocols. One using the bispectral index monitor and one using the MAC alerting protocols.

Primary Outcome Measures :
  1. The Percentage of Incidences With Explicit Recall in the BIS Versus MAC Alert Groups. [ Time Frame: Outcome of awareness is assessed 30-days after the operation ]
    By modified intention-to-treat analysis

Secondary Outcome Measures :
  1. Number of Participants With Dreams During Anesthesia Compared Between MAC or BIS Monitoring [ Time Frame: During surgery (45 minutes - 18 hours), measured based on 30 day interviews ]
    Binary variables for whether participants recall dreaming or not.

  2. Percentage of Cases With Electronic Alerts [ Time Frame: During surgery: (45 minutes - 18 hours) ]
  3. Overall Use of Anesthetics Comparing the BIS to MAC Alerts. [ Time Frame: During surgery (45 minutes - 18 hours) ]
  4. Time Till Discharge Readiness [ Time Frame: During recovery room stay: 30 minutes to 6 hours ]
    measured in time within Post Anesthesia Care Unit ( PACU) until the participant is ready for discharge from PACU based on a composite of factors, including pain and neurologic status

  5. Number of Participants Without Nausea or Vomiting [ Time Frame: During recovery room stay: 30 minutes to 6 hours ]
  6. Comparison of the Prospective and Retrospective Approaches to the Study Awareness Incidence. [ Time Frame: 30 days after surgery ]
    There is controversy regarding the appropriate technique for assessing awareness during anesthesia with explicit recall. A total cohort was utilized to compare the incidence of awareness with recall as determined by formal interview vs. the incidence of awareness with recall based on spontaneous reports (in the same cohort).

Other Outcome Measures:
  1. Relationship Between BIS Values and Hemodynamic Parameters. [ Time Frame: Outcome of hemodynamic stability is assessed ]
  2. The Relationship Between Cumulative Deep Hypnotic Time, Anesthetic Doses, and Mortality. [ Time Frame: Outcome of mortality is assessed ]
  3. Predictors of Post-traumatic Stress Disorder Based on the Type of Awareness Event. [ Time Frame: Outcome of post-traumatic stress disorder is assessed with the covariate of awareness ]
  4. Anesthetic Induction Doses, Hypotension, and BIS Values. [ Time Frame: Outcome of hypotension in relationship to induction doses and BIS values will be assessed ]
  5. Meta-Analysis of Awareness Events in Conjunction With the BAG-RECALL Study Based at Washington University. [ Time Frame: Outcome of awareness is assessed ]
  6. Incidence of Post-traumatic Stress Disorder. [ Time Frame: NEED VALUE HERE ]

Information from the National Library of Medicine

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Ages Eligible for Study:   18 Years to 100 Years   (Adult, Older Adult)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   No

Inclusion Criteria:

  • At least 18 years of age, English-speaking, available for follow-up interview at one month.

Exclusion Criteria:

  • Pre-existing neurologic or neuropsychiatric condition, surgical manipulation around forehead, not available for follow-up interview.

Information from the National Library of Medicine

To learn more about this study, you or your doctor may contact the study research staff using the contact information provided by the sponsor.

Please refer to this study by its identifier (NCT number): NCT00689091

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United States, Michigan
University of Michigan Medical School, University Hospital
Ann Arbor, Michigan, United States, 48109
Sponsors and Collaborators
University of Michigan
Foundation for Anesthesia Education and Research
American Society of Anesthesiologists
Washington University School of Medicine
University of Chicago
University of Manitoba
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Principal Investigator: George A. Mashour, M.D., Ph.D. University of Michigan
Publications automatically indexed to this study by Identifier (NCT Number):
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Responsible Party: George Mashour, Assistant Professor of Anesthesiology and Neurosurgery, University of Michigan Identifier: NCT00689091    
Other Study ID Numbers: HUM00013626
First Posted: June 3, 2008    Key Record Dates
Results First Posted: November 17, 2014
Last Update Posted: December 7, 2017
Last Verified: November 2017
Keywords provided by George Mashour, University of Michigan:
BIS Monitor
electronic alerts