A newer system intended to alert doctors when patients are regaining consciousness while under general anesthesia has not lowered incidence of anesthesia awareness any better than conventional monitoring systems, according to new research.

The study, published in the New England Journal of Medicine, analyzed a subset of more than 6,000 surgical patients at Washington University School of Medicine who doctors believed had a high risk of anesthesia awareness, also known as unintended intraoperative awareness. The situation occurs when a patient becomes aware of his or her surroundings during surgery and remembers experiencing pain or distress during the operation. Between one in 500 and one in 1,000 surgical patients experience the condition, according to the research, which said individuals with such memories sometimes develop post-traumatic stress disorder and often need psychological help.

The newer technology, which was approved by the Food and Drug Administration, is called a bispectral index (BIS) monitor. The device measures brain activity to determine how deeply a patient is anesthetized. Dr. Michael S. Avidan, the lead author of the study and professor of anesthesiology at Washington University School of Medicine, said that while BIS monitors are often considered a more accurate way of tracking awareness than an alternative approach that measures anesthesia levels in a patient's breath, the trial did not support that view.

This trial showed that the BIS measurement does not appear to be superior, he said.

Although a 2004 study found that using BIS monitors could reduce cases of intraoperative awareness by 82 percent, a 2008 study by Avidan and his colleagues determined that while BIS monitors might be slightly more beneficial, it was not effective enough confer a clinically meaningful advantage. In the newest study, investigators found that 19 out of 2,861 high-risk surgical patients in the BIS monitor group experienced either definite or possible anesthesia awareness, compared to eight out of 2,852 among those who were monitored via the exhaled anesthesia technique.

Our study does not show that the BIS monitor is ineffective, explained study co-author Dr. Henry E. Mallinckrodt. It's just that it's not superior to the protocol based on measuring the concentration of anesthetic a patient actually has received, which is a simpler and less expensive approach.

Avidan added that the findings imply that the current widespread use of BIS monitoring systems in operating rooms should be reconsidered.

New technology has to prove its superiority over more cost-effective alternatives, he said.

Old or new, cheap or expensive - patients just don't want to experience the eerie sensation that comes with suddenly recognizing that you're under the knife.

The Los Angeles Times reports that one 72-year-old man undergoing heart surgery reported that he, could hear knives (like a buzzing sound.) I could hear and feel the saw cutting into me, but I was not in pain. I felt warm water or blood running inside me...I was very afraid. I felt like my wife, my kids, and everyone had abandoned me.

Similarly, one man said he heard clinking sounds, like someone was sorting cutlery while another said he felt like [he] was drowning...it seemed like a long time.

Individuals at particular risk for experiencing anesthesia awareness include patients undergoing cardiac surgery, those who regularly consume large quantities of alcohol and those who take sedatives or certain types of pain-killing drugs.

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