Central Nervous System Monitoring; Reduction of Information Content of Quantitative Electroencephalograms for Continuous On-Line Display During Anesthesia

Abstract

Due to technical difficulties, monitoring of the main target organ influenced by the anesthetist - the central nervous system — has advanced rather slowly in comparison to, for example, monitoring of circulation parameters (for review see Pichlmayr et al. 1983 and Freye 1990). Recording microvolts in an environment where millionfold larger potential differences are induced by electromagnetic fields had to await a certain level of technical progress before monitoring of the brain's electrical activity became easy and reliable enough to be used in routine work. The separation of the amplifiers' power supply and the general power line by using rechargeable batteries followed by transmission of the signals via optical fibres (Hofmann et al. 1990) fulfilled one of the most important requirements for artefact-free recording. The second major technical breakthrough consisted in the feasibility of real-time, on-line recording and display of the frequency-analyzed signals from 17 electrode positions providing the base for true on-line monitoring with a high time resolution of 4 s (Dimpfel 1993).