Patients say it feels like being trapped in a corpse: They wake up during surgery, unable to move or scream. Some remember hearing their surgeons talk, and a few recall feeling intense pain.

Some experts have said special brain-wave monitors were the best way to prevent anesthesia awareness. Now, in a big setback for efforts to prevent it, the first large, independent test of the monitors shows they are no better than older technology.

Researchers at Washington University School of Medicine in St. Louis compared two groups of about 1,000 patients each, all deemed at high risk of waking up during surgery because of health conditions, medication or other factors.

One group used the leading brain-monitoring system, which uses electrodes on the forehead to measure brain waves and software to calculate likelihood of consciousness. The other used an older device that analyzes exhaled anesthetic gas.

Anesthesiologists watched for movement and changes in vital signs and followed protocols to maintain patients’ depth of sleep, adjusting anesthesia levels as needed. Patients were interviewed after their surgeries about what they remembered.

Two people in each group had experienced awareness – and the two monitored with the newer system reported having felt pain as well.

Lead researcher Dr. Michael Avidan said that in two of those cases – one with each system – the monitors indicated no problems with the anesthesia. In the other two cases, the monitors signaled problems.

The study analyzed groups of people who had surgery at the university’s partner hospital, Barnes-Jewish in St. Louis, in 2005 and 2006. It was published in today’s issue of the New England Journal of Medicine.

Anesthesia awareness occurs in 1 or 2 of every 1,000 surgical patients – possibly more often in children – and is thought to happen to roughly 30,000 Americans each year.

Some just have fleeting memories of things they heard, but others describe “white-hot pain” and terror.

Carol Weihrer of Reston, Va., said that 11 years after awakening during surgery to remove a diseased eye that caused severe pain, she still has post-traumatic stress disorder, can sleep for just short periods and suffers mood swings and panic attacks.

Weihrer, who founded the group Anesthesia Awareness Campaign Inc., said she heard the doctor give instructions: “Cut deeper, pull harder.” “I actually saw them cut the optic nerve when everything went black,” she said.

“While you’re laying there on the table,” she recalled, “you are thinking, praying, cursing, plotting, pleading, trying to crawl off the gurney, trying to kick, scream, move any part of your body to let them know you’re awake. In effect, you are entombed in a corpse.”