Horror stories abound of surgery patients being aware they’re being operated on, but unable to move or say anything. A new type of monitoring should help prevent that happening.

For every 1000 patients operated on, it’s thought that up to 2 become aware during surgery. This can be reduced, an Australian study suggests, by monitoring brain patterns during the operation to guide the administration of general anesthesia.

Monitoring the “bispectral index” (BIS) of brain EEG patterns indicates the depth of anesthesia and helps the anesthesiologist make adjustments, according to Dr. Paul S. Myles from the Department of Anesthesia and Pain Management at the Alfred Hospital in Melbourne, and colleagues.

However, they note in this week’s issue of The Lancet medical journal, the value of BIS “as a monitor for awareness has not previously been assessed in a randomized trial.”

To investigate, the team randomly assigned 2463 surgery patients to BIS-guided anesthesia or standard care. The patients were questioned about their awareness of the procedure a few hours, one day, and one month after surgery by a researcher who did not know which group they were in.

There were two reports of awareness in the BIS group compared with 11 in the standard care group, meaning that BIS-guided anesthesia reduced the risk of awareness by 82 percent.

“BIS monitoring had little effect on the time needed to recover from general anesthesia, as measured by eye opening, and no measurable effect on the risks of postoperative complications,” the team notes.

They conclude, based on their results, that “greater use of BIS monitoring is warranted.”

This study is a “great advance,” two clinicians from Sweden write in an editorial.

“In addition to immediate suffering due to pain and anxiety, other psychological symptoms, or even post-traumatic stress disorder, might follow after awareness,” Drs. Claes Lennmarken from University Hospital in Linkoping and Rolf Sandin from the Karolinska Institute in Stockholm comment.

“Clearly the data show that cerebral monitoring has the potential to further reduce the rate of awareness compared with traditional measures,” they write.

SOURCE: Lancet, May 29, 2004.