Researchers know that patients in some circumstances can hear conversations in the operating room. And, even feel the pain of surgery even though they appear to be fully under the anesthetic.

Science Specialist Ed Yeates joins us tonight from the University of Utah with a special report. How often does this happen?

Anesthesiologists say wakefulness in surgery is rare--probably less than one percent. But when you consider 25-million anaesthetics administered in hospitals every year, even less than one percent involves thousands of people.

((JEANETTE TRACY: "AND THEN WHEN I HEARD THE SURGEON ASK FOR THE SCALPEL, I JUST SCREAMED AS LOUD AS I COULD IN MY HEAD, IN MY MIND, TRYING TO GET MY VOICE OUT."))

At her home in Virginia, Jeanette Tracy communicates with people all over the country. As a patient who heard and felt her surgery, she's become a national spokesperson for others.

And, closer to home--Winnie Rozzo refinishes furniture at her home in Evanston, Wyoming. But she too remembers her experience in California four years ago.

((WINNIE ROZZO: "THE FIRST THAT I WAS AWARE OF WAS THIS TERRIBLE, TERRIBLE BURNING IN MY LEFT LEG WHERE THEY WERE HARVESTING THE VEIN TO PUT INTO MY HEART."))

(("IN MY MIND I WAS SCREAMING AT THE TOP OF MY LUNGS, BUT THERE WAS NOTHING COMING OUT."))

Doctors thought Winnie was fully under. The anesthetics had paralyzed her muscles so she couldn't move, but she was still experiencing levels of consciousness.

(("AND I TRIED TO MOVE MY HAND OR SOMETHING TO GET SOMEBODY'S - LIKE HELLO, AND NOTHING MOVED AT ALL."))

Winnie's experience is why anesthesiologists were especially careful when she came to the University of Utah for surgery last year.

(("NO, I REMEMBER TWO AND THAT'S ABOUT IT"))

That's also why Dr. Talmage Egan and his colleagues are looking at some new machines which may detect unseen signs of wakefulness.

One of the newer systems monitors brain wave activity--an effective way to measure the depth of consciousness--whether a patient is really under. This patch attached to the face picks up facial movements which identify feelings of pain - grimaces anesthesiologists and surgeons cannot see.

As the volunteer goes under, researchers administer levels of discomfort to see if the device quickly identifies what the patient feels.

((TALMAGE EGAN M.D., U OF U DEPT OF ANESTHESIOLOGY: "WE HAVE VARIOUS WAYS OF MEASURING WHETHER PEOPLE ARE ADEQUATELY ANESTHESIZED BUT WE DON'T HAVE A GOOD WAY YET TO BE SURE THAT THE PATIENT IS ENTIRELY UNCONSCIOUS."))

Some say why not just give everybody enough anesthetic to knock them way out. It's not that easy. Too much is risky for the patient. New monitors that watch levels of consciousness. Those devices, Dr Eagen says, are the kind of backup anesthesiologists need.