Keeping a patient asleep during surgery is a delicate operation

The word anaesthesia comes from the Greek and means “without sensation”. It describes a continuum whereby consciousness, recall and reflexes are gradually lost.

Anaesthetic awareness is a rare condition whereby patients wake up during surgery because they are underanaesthetised. As the latest research shows it doesn't happen very often – 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 professionals 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.

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. When gaseous anaesthesia was used in higher concentrations in the past, the risks and side effects of having a general anaesthetic were greater.

Safer

Anaesthesia is estimated to be about 50 times safer now than it was in the 1980s. Modern muscle-relaxant drugs make it 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 more likely to occur 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.

The portrayal of accidental awareness during general anaesthesia in the film Awake was at the extreme end of the spectrum. About 30 minutes into the film, the patient, played by Hayden Christensen, feels a scalpel cutting into his chest. The audience can hear the patient's screams, while the onscreen characters see only a man, lying inert on the operating table, apparently unconscious. However, this portrayal owes more to artistic licence than to reality.