Study Evaluating Impact of Anesthetic Management on Patient Mortality One Year after Surgery Published in Anesthesia & Analgesia.

NEWTON, Mass. -- -Study indicates that mortality may be associated with anesthetic depth-

Results from a prospective study of 1,064 adult patients evaluating potential predictive indicators of mortality following major non-cardiac surgery were published as the lead article in the January 2005 issue of Anesthesia & Analgesia. The study was conducted at the University of Florida in Gainesville and Aspect Medical Systems' BIS(TM) monitoring technology was used to measure anesthetic depth. Statistical analysis revealed that pre-existing medical illness, low blood pressure during surgery and duration of deep anesthesia were independent predictors associated with one-year mortality. Although patient illness was the most significant predictor of mortality after surgery, the study revealed a new association between mortality and cumulative deep anesthesia time, as measured by BIS.

"While our study does not demonstrate a causal link between deep anesthesia and mortality, these results raise important new questions about possible relationships between the two," said Terri Monk, MD, lead investigator of the Florida study, and now Professor of Anesthesiology at Duke University. "Anesthesia providers cannot control the age or illness of the patients they care for, but they can adjust the depth of anesthesia. If causality between deep anesthesia and post-surgical mortality is established through further research, we will want to take measures to avoid excessively deep anesthesia."

Doctor Monk's comments were further emphasized in an accompanying editorial written by Neal H. Cohen, MD, which stated, "The impact of the study, should the findings be validated, could result in major changes in how anesthesia is provided, what anesthetics are used, and how hemodynamic variables are controlled during surgery."

Following the initial report of the University of Florida study, an investigation of 5,057 non-cardiac surgery patients in Sweden also found duration of low BIS values to predict mortality during the first year following surgery. "The similarity between these two studies is striking," stated Monk. "In anesthesiology, we've historically focused on relatively short term outcomes following anesthesia and surgery, but these results suggest a possible prolonged influence of anesthesia management on patient outcomes."

In response to these and other emerging studies focused on patient outcomes, the Anesthesia Patient Safety Foundation (APSF) convened a multidisciplinary expert panel in September 2004 to discuss how surgery and anesthesia care could influence survival over a longer time span. The panel agreed that surgery and anesthesia may have a more significant and long-term impact on patients than previously realized and developed a "roadmap" for further research and action related to the long term impact of anesthesia and surgery. More information about the panel meeting can be found at http://www.apsf.org/initiatives/outcomes.mspx.

Scott Kelley, MD, Aspect's medical director, commented on the study and the APSF panel meeting. "BIS monitoring provides an important additional tool to explore differences between anesthetic techniques and to identify those techniques associated with the best outcomes," stated Kelley. "These studies highlight the critical role of the anesthesia provider in the care of millions of patients undergoing surgery each year. We are committed to working with the anesthesia specialty to develop a greater understanding of the potential associations uncovered in this research in an effort to further advance patient safety and improve outcomes."

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 9.7 million patients and has been the subject of approximately 1,700 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 release are forward-looking and may involve risks and uncertainties, including statements concerning the relationship between depth of anesthesia and post-operative mortality and the use of BIS monitoring to make better informed decisions in order to achieve optimal anesthesia. There are a number of important factors that could cause actual results to differ materially from those indicated by these forward-looking statements. These factors include a number of risks facing the Company's business. For example, the Company may not be able to demonstrate any further relationship between depth of anesthesia and post-operative mortality. There are additional factors that could cause the Company'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 the Company's Quarterly Report on Form 10-Q for the fiscal quarter ended October 2, 2004, as filed with the Securities and Exchange Commission. In addition, any forward-looking statements represent the Company's views only as of the date of this press release and should not be relied upon as representing the Company's views as of any subsequent date. While the Company 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 the Company's views as of any date subsequent to the date of this press release.

Information on the apsf.org Web site is not incorporated in 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.