The bispectral index device monitors brain waves during surgery and use a proprietary algorithm to give them a numerical score. The higher the score, the more awake the patient is. Another way to gauge the capability of anesthesia is to measure the concentration of anesthetic gases in a patient's breath.
The device "can prevent both too little anesthesia, which could cause awareness, and too much anesthesia, which could cause prolonged recovery and anesthetic side effects" such as grogginess and nausea, said Aspect's medical director, Boston anesthesiologist Dr. Scott Kelley.
According to a 2004 study, using the monitor could minimize the risk of anesthesia awareness, a finding that researchers say lacks sufficient evidence.
Lead investigator Dr. Michael Avidan said they studied the results of 2,000 surgery patients at Barnes Jewish Hospital in St. Louis. They monitored half with the bispectral device, and the others with a gas device.
The addition of the bispectral index did not demonstrate decreasing the incidence of anesthesia awareness compared with an alternative protocol that was based on an alarm going off if the anesthesia gas dropped below a certain level.
Dr. Avidan said they found that two patients in each group experienced awareness during their operation and felt pain as well.
Anesthesia awareness happens in 1 or 2 surgical patients in 1,000. It occurs when a patient wakes up during surgery, but still has enough anesthesia to prevent them from moving or speaking to let the surgeon know they are awake and can feel pain. The situation may also lead to posttraumatic stress disorder.
The study is published in the March 13 issue of the New England Journal of Medicine.
