Awake-During-Surgery Device Worth a Nod?
Study Challenges Benefit of BIS, a Brain Monitor That Helps Doctors Detect When Patients Are Waking
March 12, 2008 --Doctors don't need a widely used brain monitor to cut
patients' risk of waking during surgery, a new study suggests.
Doctors call it "unintended intraoperative awareness" or "anesthesia
awareness." Patients call it downright scary. It happens rarely -- to
about one or two out of 1,000 surgery patients -- but it does happen:
During surgery, patients become aware of things that are happening to them.
They may feel pain, discomfort, and fear.
Paralyzed by anesthesia, they are unable to tell anyone what is happening to
them. The experience usually is painless, and usually is brief. But once in a
while it leaves patients deeply traumatized, says anesthesiology professor
Michael Avidan, MB, BCh, of Washington University School of Medicine, St.
"Anesthesia awareness can be understood as people undergoing general
anesthesia and having some sensory stimuli during the procedure -- something
visual or auditory or painful -- which they remember afterward," Avidan
tells WebMD. "It is often the case that it is not disturbing, that it is a
brief experience, and patients do not complain of any long-term effects. But a
certain proportion of patients will experience negative psychological
consequences and even have posttraumatic stress disorder."
Some patients are at 10 times higher risk of anesthesia awareness than other
patients. One in 100 of these patients experience a "waking" event.
These high-risk patients:
- Undergo intensive surgeries such as open-heart surgery or lung surgery,
- Are very ill with underlying diseases, such as heart conditions, that make
it difficult for doctors to induce deep anesthesia, or
- Frequently use strong painkillers or alcohol.
(Have you been awake or
aware during surgery? Share your experience on WebMD's
Health Cafe message board.)
Does BIS Brain Monitor Cut Waking During Surgery?
The bispectral index (BIS) monitor is supposed to help doctors know when
patients are waking. The device, made by Aspect Medical Systems, uses a simple
array of electrodes attached to a patient's forehead to monitor brain
The device then uses a secret, proprietary algorithm to calculate a
consciousness-level score. On a 0 to 100 scale, where zero is no brain activity
and 100 is full consciousness, patients with a score of 40 to 60 are not
supposed to experience anesthesia awareness.
In 2004, a clinical trial suggested that the device cut the risk of
anesthesia awareness among high-risk surgery patients. Driven by media reports
of patients who experienced waking during surgery -- and by a frightening
Hollywood movie, Awake -- Advent's device became widely used. It's now
found in about 60% of all U.S. operating rooms and is used in about 17% of
surgeries requiring general anesthesia.
But does the device work better than the standard technique tracking the
amount of anesthetic gas a patient exhales? Avidan and colleagues tested this
in a new clinical trial that enrolled patients with at least one factor that
put them at high risk of anesthesia awareness.