Assessing level of sedation in critically ill patients is an integral part of intensive care practice. Sedation scales, such as the Richmond Agitation-Sedation Score (RASS) 1, have been developed, but are imperfect in a general population and of limited use when muscle relaxants are administered. Instruments have been developed to examine cerebral electrical activity using processed EEG in an attempt to determine state of awareness.2 The Bispectral Index (BIS) is a statistically derived measure of cerebral electrical activity to assess cortical-subcortical interaction. The BIS was determined by repeated studies on patients anesthetized in the operating room (OR) with the assumption that sedation is associated with a lack of awareness and recall.2 The Patient State Analyzer (PSA 4000) is a 4-channel processed EEG reading using an advanced algorithm that interprets changes in regional brain activity providing a numerical assessment (ranging from 0-100; 0 = no central nervous system [CNS] activity, 100 = awake) to assess the degree of sedation. The PSA 4000 (PSA) is an advancement over the BIS monitor as the BIS is a single channel whereas the PSA is a 4-channel monitor.

Additionally, the PSA monitor has new proprietary software for analysis of the EEG data. The PSA is relatively new and thus there is little published data to evaluate its use in the operating room (OR) or the intensive care unit (ICU).