Study Evaluating Whether the Bispectral Index Prevents Patients at Higher Risk From Being Awake During Surgery and Anesthesia

The incidence of anesthesia awareness (AA) is 0.1-0.2% and may result in post traumatic stress disorders. For some patients, owing to illness, medications, substance misuse or surgery, the risk approaches 1%. The B-AWARE Study by Myles et al. suggested that the bispectral index (BIS) monitor, which reportedly reflects anesthetic depth, may decrease the incidence of AA in higher risk patients by 82%. The American Society of Anesthesiologists has published a practice advisory on AA, which does not recommend the routine use of cerebral function monitors. We propose to test the hypothesis that an anesthetic protocol based on BIS decreases the incidence of AA among higher risk patients compared with an anesthetic protocol based on the end-tidal anesthetic gas (ETAG) concentration. We have completed a randomized, single-blinded prospective feasibility study (The B-Unaware Trial) which enrolled 2000 patients at higher risk for AA. Four patients (0.21%; 95% CI=0.06% to 0.57%) had definite AA, of whom two were in the BIS-guided group and two in the ETAG-guided group. Nine patients (0.46%; 95% CI=0.22% to 0.91%) had definite or possible AA, of whom six were in the BIS-guided group and three in the ETAG-guided group. The BAG RECALL study will be a multi-center, prospective, single-blinded, randomized study enrolling 6000 patients at higher risk for AA. The BAG RECALL study is adequately powered and rigorously designed to answer with a reasonable degree of scientific probability whether BIS guidance results in clinically relevant reduction in anesthesia awareness among higher risk patients undergoing general anesthesia.

At the University of Michigan, a parallel study will be conducted - Michigan Awareness Control Study, MACS (NCT00689091) - enrolling 30,000 patients to assess whether the BIS monitor decreases the likelihood of anesthesia awareness among all patients undergoing general anesthesia, regardless of their risk profile. The investigators of this study and the BAG-RECALL study have collaborated in designing these studies and are pre-specifying that common outcome measures will be examined collaboratively including data from both studies.

Inclusion criteria

MUST HAVE:

General Anesthesia with volatile anesthetic

PATIENT CHARACTERISTICS

Major Criteria (Must have any 1 of the following:)

• Planned open heart surgery
• Medications - anticonvulsants, abuse of opiates, benzodiazepines, cocaine
• EF<40%
• Prior history of awareness (recall)
• History of difficult intubation or anticipated difficult intubation
• ASA IV or V status
• Aortic stenosis
• End stage lung disease
• Marginal exercise tolerance not secondary to musculoskeletal dysfunction
• Pulmonary hypertension
• Daily alcohol consumption

Exclusion criteria

• Surgical procedure that prevents the use of the BIS (e.g. surgery of forehead)
• Patient positioning prevents use of the BIS
• Surgery with wake-up test.
• Less than 18 years of age
• Vulnerable populations, such as those with dementia and those unable to provide informed consent.
• Stroke with residual neurological deficits

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