MEDICAL MATTERSAnaesthesia awareness is a rare condition whereby patients wake up during surgery
"Mr Anaesthetist, if the patient can keep awake, surely you can."
- Wilfred Trotter, consultant surgeon
This quote, attributed to a no-nonsense general surgeon who practised at University College Hospital, London in the early 20th century, is not what patients facing a general anaesthetic want to hear.
Especially those who may have seen or read about the film Awake, last year's medical thriller from director Joby Harold. About 30 minutes into the film, the main character, played by Hayden Christensen, feels the scalpel cutting into his chest.
The audience can hear the patient's screams of agony, while the onscreen characters see only a man, lying inert on the operating table, apparently unconscious.
Christensen, who is about to undergo heart transplantation, is experiencing anaesthesia awareness, a rare but recognised condition whereby patients wake up during surgery because they are under-anaesthetised. It doesn't happen very often - anaesthesia awareness has a generally accepted incidence of 0.2 per cent - but when it does it can have immediate physical and long-term psychological consequences.
There are two types of anaesthetic awareness: explicit awareness means the patient can recall the words and actions of the health professional in the operating theatre. Implicit awareness usually presents some time after the surgery, with nightmares, sleep disturbance and flashbacks. At its worst, post traumatic stress disorder may result.
The first general anaesthetic was given more than 150 years ago. Ether was first used for dental extractions in the US in the 1840s. On December 21st, 1846, the British surgeon Robert Liston amputated a diseased leg at the thigh from a patient who had been anaesthetised with ether.
"This Yankee dodge, gentlemen, beats mesmerism hollow," Liston pronounced afterwards.
Even with modern drugs and techniques, keeping a patient asleep during surgery is a delicate balancing act. Gaseous anaesthetics are used in combination with intravenous agents to induce and maintain general anaesthesia.
Before the advent of intravenous drugs, much deeper gaseous anaesthesia was needed, leading to an unpleasant recovery and high mortality.
But deaths from general anaesthesia have dropped dramatically. According to the American Society of Anaesthesiologists, the risk of death in a generally healthy patient is now one in 250,000 cases, a considerable drop from a mortality rate of one in 10,000 two decades ago.
One of the "fathers" of modern anaesthesia was Prof Cecil Gray, professor of anaesthesia at Liverpool University from 1959 to 1976, who died earlier this year. He was one of the pioneers of the use of the muscle relaxant, tubocurarine chloride, derived from the South American arrow poison, curare, in general anaesthesia.
Modern relaxant drugs help to relax the abdominal and thoracic muscles and make it a lot easier to perform major surgery.
But anaesthetic awareness is more common among patients who receive neuromuscular blocking drugs, because they cannot signal to the medical team they are conscious.
Awareness is also more likely when an anaesthetic is given as an emergency, for example after trauma or to facilitate an emergency Caesarean section.
Heart and lung surgery is also associated with a slightly higher incidence of anaesthetic awareness.
So what are doctors doing about the problem? Much research effort has been expended in developing devices that monitor the depth of anaesthesia. The bispectral index system (BIS) processes brain wave readings and alerts the anaesthetist if the depth of anaesthesia is inadequate.
Despite initial enthusiasm, more recent studies indicate that using a BIS device does not, in fact, improve the experience of people at high risk of anaesthetic awareness.
Writing in last week's New England Journal of Medicine, Dr Beverley Orser of the Department of Anaesthesia at Toronto University, Canada, said: "We must remember that the [ brain] signals detected by monitors may or may not represent physiological process of interest, such as learning and consciousness."
General anaesthesia may have come a long way since 1840, but a solution to the problem of intraoperative awareness depends on developing a better understanding of how and where in the brain anaesthetic agents act.