[Conscious and unconscious awareness during anesthesia--how deep is the patient's sleep?]

A review is given over the aspects of awareness during general anaesthesia. Traditional clinical signs for evaluating depth of anaesthesia can be supplemented by objective methods such as EEG, cerebral function monitor and sensory evoked potentials. However, it has been difficult to establish the practical applications of these methods. Awareness can be graded from the obvious form, with recall of intraoperative events, to an unconscious form where the memory can be activated through special psychological techniques. We discuss the possibility of using unconscious perception of auditory signals for positive instructions to patients under anaesthesia.