Patients can be aware during operations

The device, tested by doctors in Melbourne, Australia, measures brainwaves to test for patients' awareness while under anaesthesia.

The monitor can cut cases of pain during surgery by 80%, New Scientist magazine reported.

It is thought one in 1,000 patients has some memory of their operation. Some can be in agony while paralysed by the anaesthetics, unable to tell surgeons.

'I WOKE UP DURING SURGERY' I felt the cutting. It was like a burning feeling - excruciating. I couldn't move or flinch or anything Linda McDougall, who experienced awareness during a Caesarean

Linda McDougall, who experienced awareness during a Caesarian operation, said: "I felt the cutting. It was like a burning feeling - excruciating.

"I couldn't move or flinch or anything, but my heart was beating so fast I thought I was going to have a heart attack.

"When they pulled Daniel out, I heard the doctor say: 'Every birth is a miracle. We have a beautiful baby boy.'"

The operation was 17 years ago in Melbourne, Australia, and she said: "For the first couple of years, it was frightening. Now I just get a bit teary when I talk about it."

The BIS monitor is a kind of electroencephalogram (EEG) which detects electrical activity in the brain through a single electrode on the forehead.

The activity depends on metabolism, memory function and state of consciousness, which are all affected by anaesthetics.

The monitor analyses brainwaves to produce a scale of awareness - 100 is wide awake, while between 40 and 60 is the recommended score for someone under anaesthesia.

The device is already used in the US, where the Food and Drug Administration has licensed it for use to prevent awareness during operations.

Remembered

A trial followed 2,500 patients undergoing surgery in 24 hospitals in Australia, New Zealand, the UK and Hong Kong.

They were at high risk of awareness because they had experience of it before or were having operations where light anaesthesia is preferable, such as heart surgery or a Caesarean.

Some were put under a BIS monitor, while the others were given routine assessment, which involves looking out for sweating, movement or increases in blood pressure and heart rate.

Interviews were carried out with patients four hours, one day and 30 days after surgery to see if they remembered their operation.

Of the routine care group, 11 experienced awareness, while for the BIS group, two did.

The Australian researchers believe the monitor should be used in high risk cases, particularly as they say anaesthetists underestimate the frequency of awareness under surgery.

Professor Gavin Kenny, at the University of Glasgow's anaesthesia unit, has led the development of a different device - the Auditory Evoked Potential System.

This gives a stimulation to the brain in the form of a "click" which is processed by the brain. This process is affected by the anaesthetics and can be measured.

Professor Kenny said this was better than the BIS monitor which "can give an inaccurate reading".

He added: "Some types of anaesthetics make the BIS rise, though the patient is actually going down."

Rolf Sandin, at the Karolinska Institute, Sweden, said in New Scientist: "We should see more of this sort of monitoring.

"But before we recommend they be used on every patient, we need an improvement in sensitivity and specificity."