Awareness during anesthesia--an update.

General anesthesia is a reversible state characterized by unconsciousness, analgesia, muscle relaxation, and depression of reflexes which is achieved by the administration of chemical agents. It is a balance between the amount of anesthetic drugs administered and the state of arousal of the patient. As the intensity of surgical stimulation varies during a surgical procedure, so does the requirement of anesthetic agents. The organ system effects of anesthetic drugs may limit the amount that can be given safely. This would, at occasions, create a critical imbalance between anesthetic requirement and anesthetic drug administration resulting in varying depth of anesthesia.