Description

Awareness during anaesthesia is rare. Its incidence is thought to be 0.18% in cases which muscle relaxants were used and 0.1% in cases which muscle relaxants were not used. Awareness is a leading factor in patients’ dissatisfaction following anaesthesia and can have a longterm impact on patient’s well being. The end-tidal anaesthetic agent concentration is one measure used to assess the level of sedation. The incidence of awareness among patients with neuromuscular block was similarly independent of whether end-tidal anaesthetic agent concentration was measured or not. The Bispectral Index (BIS, Aspect Medical Systems, Newton, MA, USA) is marketed as a device to monitor the level of sedation in the brain and to assess the risk of awareness while under sedation. In addition to BIS, auditory evoked potentials have also been evaluated for these purposes. In this review, a brief description of BIS (XP, version 3.12), its clinical applications and its limitations are given.