Awareness during anaesthesia: a review.

Following the introduction of muscle relaxants into anaesthesia there became recognised a state in which patients may be aware of their surroundings but unable to communicate their plight. This state of awareness is more likely to occur during light inhalational or total intravenous anaesthesia. Detection of awareness is difficult and several methods have been described. Measurement of the depth of anaesthesia is also difficult as clinical signs are unreliable and even sophisticated monitoring equipment is unhelpful. Awareness can occur without patient recall and may be due to equipment failure or anaesthetic failure. The former is avoidable and the latter ought to be. Recommendations have been made regarding the use of premedicant drugs and volatile anaesthetic agents to reduce the incidence of awareness.