UW News

December 1, 1997

Wake up during surgery? Chances are reduced with innovative new brain wave monitors at UW Medical Center

It’s every patient’s worst nightmare: the thought of undergoing surgery with inadequate anesthesia; of feeling the cut of the surgeon’s knife, but being unable to tell anyone that you’re not completely unconscious. While such “intraoperative awareness” is an infrequent occurrence, it’s not entirely unheard of.
The chance of such a rare event is now even less at University of Washington Medical Center, one of the first hospitals in the country to install a new state-of-the-art brain-wave monitoring system in every one of its operating rooms.

“It’s something many anesthesiologists don’t like to think about,” said Dr. Andrew Bowdle, associate professor of anesthesiology at UW Medical Center. “It’s a problem to the extent that there are very few statistics on intraoperative awareness. The information is mostly anecdotal, and it hasn’t been well studied. But clearly, it happens occasionally, and when it does, it’s devastating for both the patient and the anesthesiologist. This monitor goes a long way toward preventing it.”

The new system, called the Bispectral Index, offers the first direct method of measuring the effects of anesthetic and sedative agents on the brain, using an enhanced EEG (electroencephalogram) monitor.

In addition to displaying raw EEG data, the system analyzes the patient’s brain wave pattern and converts it into a “depth of sedation” number between 0 (indicating no brain activity) and 100 (fully awake). The target number for an anesthetized patient is approximately 50 to 60.

The new system offers a number of advantages in addition to allaying patient fears about inadequate anesthesia, said Bowdle — not least of which is the cost savings from being able to administer the right amount of anesthetic agent to keep the patient’s brain waves at an optimum level. Without the system, anesthesiologists may administer more drugs than necessary to make sure their patients are completely unconscious during surgery.

Another plus: without the extra depth of anesthesia, patients awaken more quickly after surgery.

The Bispectral Index system also overcomes a disadvantage inherent in earlier use of EEG in surgical settings: the electrodes that attach to the skin are “self-prepping.” No preparation of the skin is needed other than an alcohol wipe, so the anesthesiologist can quickly prepare the patient, attach the leads and establish good electrical contacts.

“There was a lot of skepticism about this system when it was first offered,” said Bowdle. “People have been trying to use EEGs to monitor anesthesia depth for a couple of decades. But clinical trials have shown that this is really a substantial achievement.” UW Medical Center now has about 20 of the devices in use.

In fact, said Bowdle, when a patient arrived at the medical center recently carrying a copy of a Time magazine article on the device (11/3/97, p. 96), the anesthesia staff was able to reassure him that the monitor would be used during his surgery.

“This is a significant advance in the history of anesthesia — being able to accurately measure the depth of sedation by direct, noninvasive means,” said Bowdle. “We would use this system even if it weren’t reducing costs, because of its ability to reduce intraoperative awareness and shorten recovery time.”

In addition to using the Bispectral Index for routine patient care, the UW Department of Anesthesiology is doing research to further understand the use of EEG for monitoring anesthesia, under the direction of Dr. Janet Pavlin.

Unexpected wakeups occur in at least 40,000 of the country’s 20 million annual surgeries, according to Dr. Peter Sebel, an anesthesiologist at Emory University who has studied the problem. In almost all such cases, the pain killers keep working and the patient feels only pressure. But Sebel estimates that in at least 400 cases annually, patients actually feel pain. The Bispectral Index is manufactured by Aspect Medical Systems, Inc. of Natick, Mass.