Study Documents U.S. Incidence of Intraoperative Awareness

NEWTON, Mass. -- Aspect Medical Systems today announced that results from a prospective study of the incidence of awareness in the United States were published in the September issue of the peer-reviewed journal, Anesthesia & Analgesia. The study, known as the AIM trial, evaluated 19,576 patients and documented that awareness with recall occurs in the U.S. at a rate between one to two cases per 1,000 patients receiving general anesthesia. Awareness with recall occurs when patients do not receive enough anesthesia to remain unconscious. As a result, they may be awake during surgery, aware of what is happening and retain memory of this experience after the surgery is over. Studies show that awareness can be a traumatic experience for patients and result in the development of long-term psychological problems.

"This is the largest awareness incidence study ever conducted and the results demonstrate that awareness occurs at a fairly consistent rate, regardless of location," said Peter Sebel, MBBS, a professor of anesthesiology at Emory University Medical Center and lead investigator in the study. "The results of the AIM trial may be surprising to anesthesia providers because patients infrequently report awareness cases. However, our study showed that when we used a structured interview technique to follow-up with patients after surgery, one to two out of every thousand experienced explicit awareness with recall," he continued. "This suggests that we don't hear more about awareness in routine clinical practice because we don't typically look for it, but this doesn't mean that patients are not adversely affected. In fact, up to 44 percent of patients who experience awareness may suffer from psychological problems, including avoidance of medical personnel."

The AIM study confirmed 25 cases of awareness out of 19,576 patients receiving general anesthesia. Results also documented an additional 46 reports of possible awareness where investigators were not able to obtain sufficient data to confirm awareness, and 1,182 (6 percent) reports of intraoperative dreaming.

The publication of the AIM trial follows publication of two additional anesthesia trials, known as B-Aware and Safe-2. Results of the B-Aware trial, published last May in The Lancet, documented that use of BIS monitoring to help guide anesthetic dosing reduced the risk of awareness with recall in high-risk patients by 82 percent. Similarly, the Safe-2 trial, published last January in the Swedish journal of anesthesia, Acta Anaesthesiologica Scandinavica, documented that use of BIS monitoring reduced the risk of awareness in the general patient population by 77 percent.

"The anesthesia profession has a longstanding history of leading improvements in patient safety. As part of this commitment, awareness experts from around the world have collaborated to define the scope of the problem of awareness and to determine the impact of additional monitoring on patient outcomes," said Paul Manberg, PhD, vice president of clinical, regulatory and quality assurance for Aspect. "The scientific literature now documents that awareness with recall is a legitimate concern for patients and providers, and that BIS monitoring is the only technology proven to further reduce the risk of this rare, but important, adverse event."

Furthermore, a recent health economic analysis was conducted to determine a per-patient cost of BIS monitoring. The results, published in the August 2004 edition of the journal Anesthesiology, showed that the net cost of utilizing BIS technology is $5.55 per patient when the cost savings gained from decreased drug use and increased efficiency are considered. This cost can be further offset when the proven quality and safety benefits of BIS monitoring are considered, including better patient recoveries, increased patient satisfaction and reduced risk of awareness with recall.

Using a sensor placed on the patient's forehead, BIS monitoring translates information from the electroencephalogram (EEG) into a single number that represents each patient's level of consciousness. This number -- the BIS value -- ranges from 100 (indicating an awake patient) to zero (indicating the absence of brain activity). Using the BIS value to guide administration of anesthetic medication, in conjunction with other vital signs, allows clinicians to make better informed decisions to achieve optimal anesthesia.

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Source: Aspect Medical Systems, Inc.