Adequate Brain Perfusion and Oxygenation is Not Assured by a Normal Blood Pressure, Announces Somanetics.

Business Editors

TROY, Mich.--(BW HealthWire)--Oct. 16, 2001

A medical study performed at the University of Louisville Health Science Center demonstrated that brain blood oxygenation, as monitored by Somanetics' INVOS(R) Cerebral Oximeter, may decline during cardiopulmonary bypass surgery, even when blood pressure is considered to be adequate, announced Somanetics Corporation (Nasdaq:SMTS). In one-third of the cases, clinically significant declines in brain blood oxygenation occurred despite an apparently adequate blood pressure (mean arterial pressure above 70 mm Hg).

The 56-patient study was presented today at the American Society of Anesthesiologists' annual meeting in New Orleans by Harvey L. Edmonds, Jr., Ph.D., Professor and Director of Research, Department of Anesthesiology, the University of Louisville Health Science Center.

Somanetics' INVOS Cerebral Oximeter is the only patient monitoring system commercially available in the U.S. that noninvasively and continuously monitors changes in the regional oxygen saturation of the blood in the brain.

"Despite the well-known cerebral vasodilation (opening of the blood vessels to allow more flow) produced by anesthesia, measures of brain perfusion and oxygenation generally remained independent of systemic blood pressure," said Dr. Edmonds. Half of the patients in the study were anesthetized with desflurane and half with sevoflurene.

"Frequent episodes of transient cerebral oxygen desaturation, monitored by the INVOS Cerebral Oximeter and confirmed by transcranial Doppler, occurred despite presumably `adequate' blood pressure. This suggests that blood pressure as a standard physiologic measure is an incomplete indicator of perfusion and oxygenation during cardiopulmonary bypass. This observation may help explain the inconsistent association between intraoperative blood pressure and postoperative neurocognitive decline," he said.

The relationship between incidences of low brain oxygen saturation during cardiac surgery and brain injury has been reported in other clinical studies. In addition, an intervention outcome study from the Weill Medical College of Cornell University was reported at the ASA this week. The 286-patient study demonstrated that maintaining adequate regional brain blood oxygen saturation levels during cardiac surgery by monitoring with Somanetics' INVOS(R) Cerebral Oximeter patient monitoring system and making interventions as needed to maintain brain blood oxygen saturation at adequate levels, significantly decreased the incidence of stoke and coma in these patients.

Other intervention outcome studies have shown reduced incidence of neurological complications, renal failure and patient hospital and ICU length of stay by monitoring changes in regional brain blood oxygen levels and making interventions as needed.

"Before specialized monitors, blood pressure was a widely-accepted estimate of blood flow to the brain, although an admittedly indirect measure," said Dr. Edmonds. "This study is a demonstration of the potential risks associated with that approach. Using blood pressure as an estimate of adequate blood flow to the brain is frequently incorrect and misses some transient, but significant, declines in brain oxygenation that occur. The INVOS Cerebral Oximeter, a monitor that gives a direct reading of changes in regional brain blood oxygenation, is now available, affordable, easy-to-use and cost effective."

Somanetics Corporation, headquartered in Troy, Mich., manufactures and markets the INVOS Cerebral Oximeter patient brain blood oxygen monitoring system, the only noninvasive and continuous monitor of changes in regional oxygen saturation of a patient's blood in the brain commercially available in the U.S. Use of the patient monitoring system can help medical professionals, such as surgeons and anesthesiologists, identify regional blood oxygen imbalances and take corrective action. Such action can potentially prevent or reduce neurological injuries related to adverse events during surgery or in the critical care unit and reduce the associated cost of care. Somanetics also is developing the CorRestore(TM) patch for use in cardiac repair and reconstruction, including a procedure called Surgical Anterior Ventricular Endocardial Restoration, or SAVER, a treatment for patients with certain types of congestive heart failure.