NEWTON, Mass.--(BUSINESS WIRE)--May 28, 2004--Aspect Medical Systems (NASDAQ: ASPM) today announced that results from a prospective study of the potential of BIS(TM) monitoring to reduce the risk of intraoperative awareness were published in the May 29th issue (volume 363, number 9423) of The Lancet. The study, known as B-Aware, 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. The B-Aware study is one of the largest anesthesia-related investigations ever conducted and the largest to document the value of BIS monitoring in reducing the risk of patients inadvertently waking during surgery.

The B-Aware trial was a prospective, randomized, double-blind, multi-center investigation conducted in 24 hospitals in Australia, New Zealand, Hong Kong, Thailand and the UK. The study examined 2,500 patients considered to have a high risk of awareness during surgery, either because they had experienced it before or because they were undergoing procedures such as heart surgery where a light anesthetic is preferable.

Findings from B-Aware support results documented in a recent prospective Scandinavian study, known as Safe 2, published in Acta Anaesthesiologica Scandinavica in January 2004. The Safe 2 trial was a prospective historical control trial that examined the general patient population and found a 77 percent reduction in the incidence of awareness with recall when BIS monitoring was used. Safe 2 trial investigators also provided a commentary on awareness research in this issue of The Lancet.

"Publication of the B-Aware study in the prestigious journal The Lancet provides additional scientific evidence to the anesthesia community that BIS monitoring can help reduce the risk of intraoperative awareness with recall in surgical patients," said Paul Manberg, PhD, vice president of clinical, regulatory and quality assurance for Aspect. "This study joins a significant body of clinical evidence documenting the overall benefits of incorporating BIS monitoring into current clinical practice. Studies demonstrate that the device helps anesthesia providers ensure that each patient receives just the right amount of anesthetic, thereby reducing the chances of inadvertent overdosing and underdosing."

About BIS Monitoring

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.

About Aspect Medical Systems, Inc.

Aspect Medical Systems, Inc. (NASDAQ: ASPM) is a global market leader in brain monitoring technology. Aspect's BIS technology directly measures the effects of anesthetics and sedatives on the brain. The technology has been used to assess more than 8.7 million patients and has been the subject of approximately 1,400 published articles and abstracts. BIS technology is installed in approximately 32 percent of all domestic operating rooms and is available in more than 160 countries. Aspect Medical Systems has OEM agreements with seven leading manufacturers of patient monitoring systems. For more information, visit Aspect's web site at http://www.aspectmedical.com.

Safe Harbor Statement

Certain statements in this press release are forward-looking and may involve risks and uncertainties. There are factors that could cause Aspect's actual results to vary from its forward-looking statements, including without limitation those set forth under the heading "Factors Affecting Future Operating Results" in Aspect's Quarterly Report on Form 10-Q for the fiscal quarter ended April 3, 2004, as filed with the Securities and Exchange Commission. In addition, any forward-looking statements represent Aspect's views only as of the date of this press release and should not be relied upon as representing Aspect's views as of any subsequent date. While Aspect may elect to update forward-looking statements in the future, it specifically disclaims any obligation to do so, even if its expectations change. Therefore, you should not rely on these forward-looking statements as representing Aspect's views as of any date subsequent to the date of this press release.

Aspect, Bispectral Index and BIS are registered trademarks of Aspect Medical Systems, Inc. All other trademarks, service marks and company names are the property of their respective owners.