ELECTROENCEPHALOGRAM-BASED DEPTH OF ANESTHESIA MONITORS

General anesthetic agents are central nervous system (CNS) poisons. Achieving adequate depth of general anesthesia during surgical procedures is desirable. While too deep an anesthetic may result in cardiovascular depression and prolonged awakening times, a rather harmless complication of minor clinical interest, the opposite-too light anesthesia- is more difficult to detect and frightening from the patient’s point of view, and may be associated with intra-operative awareness (Ropcke, 2004). Traditionally, depth of anesthesia has been assessed from autonomic and movement responses, with efforts concentrated on maintaining cardiovascular stability along with immobility. However, movement in a non-paralyzed subject during anesthesia has been shown to represent a spinal response. Immobility is easily achieved with neuromuscular blocking agents (NMBAs). When NMBAs are used, neither immobility nor cardiovascular stability can be considered to represent depression or presence of cortical functions such as consciousness and recall. Previously, the hypnotic component in balanced anesthesia has been beyond the scope of monitoring (Rampil et al., 1993). A primary reason for the use of EEG-based monitoring in general anesthesia is to detect and warn the anesthesiologist that retrievable memories are being formed by the patient, i.e. awareness (Voss and Sleigh, 2007).