Imagine gaining a degree of consciousness in the middle of surgery and being physically unable to show any signs of discomfort. Known in the medical world as anesthesia awareness, this medical lapse has proved to be somewhat endemic for surgery patients.

According to a recent study performed by researchers at the Washington University School of Medicine, the device that doctors currently rely on to prevent anesthesia awareness may not be as effective as was once believed.

“People who are unconscious due to anesthesia expect to feel and know nothing,” Alex Evers, head of the department of anesthesiology, said. “However, some people can recall things they heard, smelled, or pain felt from the surgery.”

For minor surgeries, the incidence of anesthesia awareness occurs approximately once per 1,000 cases. But Evers said that “for high-risk patients such as alcoholics, drug addicts, or people that are undergoing big surgeries, there may be an incidence as high as one percent.”

Second-year medical student Adam Searleman, who assisted in the study, added that those high-risk patients may not respond to ansthesia as effectively.

“Sicker patients, such as those who have drug or alcohol problems, have a higher risk because they often develop a resistance to the agents used in the anesthesia,”

With roughly 40 million anesthesia patients in the U.S. each year, the tenth-of-one-percent incidence rate may appear as an insignificant figure by itself. However, the tiny percentage does amount up to a considerable number of patients experiencing awareness during surgery.

According to Michael Avidan, associate professor of anesthesiology and the lead author of the study, patients who experience anesthesia awareness often suffer from posttraumatic stress disorder.

Avidan presented a documented case in which the patient woke up in pain and fear when the paralyzing agent of anesthesia wore off after the surgery.

“I woke up, I woke up.and felt excruciating pain in my abdomen. I remember being in tremendous fear,” the patient said, as recorded in the document.

A 2004 study called “B-Aware” reported that a Bispectral Monitor Device (BIS), which is the monitoring device that most hospitals use to regulate anesthesia levels, could reduce the occurrence of anesthesia awareness by ten-fold. With BIS, doctors can ensure that the patient’s brain wave index is kept between 40 and 60, in a scale where 100 indicates full consciousness, and zero indicates no brain activity at all.

In reading the study, Evers and Avidan encountered what they saw as a fundamental flaw. The study had not compared the BIS to a control group, such as any of the other existing monitoring protocols that can reduce the risk of anesthesia awareness.

In collaboration with a number of other doctors and medical students, Avidan conducted a new study called “B-Unaware,” published in the New England Journal of Medicine on March 13. Rather than comparing the BIS monitor group to a control group that received no treatment at all, the new study compared BIS to a monitoring technique called End-Tidal Anesthesia Gas (ETAG) to test for differences in the occurrence of anesthesia awareness between the two techniques. ETAG monitors the anesthesia gas contents that the patient is breathing out during the surgery.

The researchers performed the study on 2,000 patients, with half receiving BIS monitoring and the other half receiving ETAG. The results showed that both groups had between a 0.1 percent and 1 percent incidence. The study also demonstrated that neither BIS nor ETAG were 100 percent effective at preventing anesthesia awareness.

Patients in the study who were monitored through ETAG were also attached to a BIS monitoring system, allowing the doctors to test whether BIS would have successfully prevented anesthesia awareness in the few instances in which ETAG had failed to do so. The results showed that such was not the case.

Avidan is currently expanding the study by testing more patients to determine if a larger test pool will produce any disparity between the BIS group and the ETAG group that may not have arisen in the initial study of only 2,000 patients. This new study hypothesizes that the difference will be negligible.

According to Avidan, the study suggests that BIS monitoring-a highly expensive system-may not be worth its cost.

“The intent of the research is not to attack the Bispectral Index Monitoring System itself,” Avidan said. “The intent is rather to evaluate the integrity of the system dispassionately, and with no financial interests.”

Immediately following the publication of the research, the stock of BIS plummeted 50 percent.

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