Anesthesiologist researchers did not find that brain wave monitors are superior to traditional, readily available anesthesia monitoring methods for preventing long-term psychological symptoms related to the experience of anesthesia awareness.

In a presentation at the Annual Meeting of the American Society of Anesthesiologists, researchers discussed sub-study findings of the B-UNAWARE trial, conducted at Washington University in St. Louis to determine whether a patient monitoring protocol using the BIS monitor was more effective in preventing anesthesia awareness than a simple protocol based on routine measurement of exhaled anesthetic gas. Use of the Bispectral index (BIS), developed from a processed electroencephalogram, has been reported to decrease awareness of anesthesia when the BIS value is maintained below 60.

Two thousand patients were randomized to either a BIS or end tidal anesthetic gas (ETAG) guided protocol and were assessed for anesthesia awareness at three postoperative intervals (0 to 24 hours, 24 to 72 hours, and 30 days after extubation). Patients who experienced definite or possible awareness during anesthesia were contacted at 18 to 30 months after their surgery and were asked structured questions to determine whether they experienced long-term psychological symptoms related to their awareness experience.

"Out of 2,000 patients involved in the B-Unaware trial, we found that four patients experienced definite awareness and five patients experienced possible awareness. Of those patients, six were part of the BIS protocol, suggesting that the BIS protocol was not superior in this study in preventing cases of awareness," said Michael S. Avidan, M.D., associate professor of anesthesiology and surgery at Washington University in St. Louis.

While the BIS protocol did not prevent all cases of awareness, researchers hypothesized that the BIS monitor, which alerted anesthesia practitioners with an audible alarm when the BIS number was above the recommended upper bound of 60, would prevent prolonged awareness with possible resultant long-term psychological symptoms.

Patients who experience awareness may develop long-term psychological consequences including recurring nightmares, anxiety and flashbacks. Some may even develop post-traumatic stress disorder.

Post-operative interviews were conducted with six of the eight patients with awareness experiences between eighteen months and two years after their surgery. Four of the patients contacted reported lucid memories of the procedures consistent with their original reports, but did not report negative repercussions.

Two patients reported having negative psychological impact to their daily lives as a result of their awareness experience. Both patients were part of the BIS protocol during the B-Unaware trial and reported symptoms included avoidance behavior, recurrent nightmares, social debility and depression. Both patients have sought counseling to help cope with their symptoms.

"The follow-up interviews conducted as a part of this sub-study found that long-term psychological symptoms were not prevented by the BIS protocol," Avidan concluded. "Similar to previous study findings, we found that the majority of anesthesia awareness episodes did not have a negative long-term psychological or emotional impact for patients."