Bispectral index (BIS) monitoring has been used to monitor sedation depth, to avoid introperative awareness and to adjust the dosage of intraoperative hypnotics. Several investigations tried to find BIS's efficacy in managing sedation of critically ill patients. In spite of some controversies, BIS monitoring seem to be beneficial: it does not require additional stimuli to determine sedation level which is essential in other subjective modalities, such as Ramsay score, and usually compromises the already instituted patient's sedation level.