Monitors
Recent advances have led to the manufacture of monitors of awareness. Typically these monitor the EEG, which represents the electrical activity of the cerebral cortex, which is active when awake but quiescent when anesthetized (or in natural sleep). The monitors usually process the EEG signal down to a single number, where 100 corresponds to a patient who is fully alert, and zero corresponds to electrical silence. General anesthesia is usually signified by a number between 60 and 40 (this varies with the specific system used). There are several monitors now commercially available. These newer technologies include the bispectral index (BIS), EEG entropy monitoring, auditory evoked potentials, and several other systems such as the SNAP monitor and the Narcotrend monitor.
None of these systems are perfect. For example, they are unreliable at extremes of age (e.g. neonates, infants or the very elderly). Secondly, certain agents, such as nitrous oxide, ketamine or xenon, may produce anesthesia without reducing the value of the depth monitor. This is because the molecular action of these agents (NMDA receptor antagonists) differs from that of more conventional agents, and they suppress cortical EEG activity less. Thirdly, they are prone to interference from other biological potentials (such as EMG), or external electrical signals (such as electrosurgery). This means that the technology that will reliably monitor depth of anesthesia for every patient and every anesthetic does not yet exist.
Read more about this topic: Anesthesia Awareness
Famous quotes containing the word monitors:
“To anybody who can hold the Present at its worth without being inappreciative of the Past, it may be forgiven, if to such an one the solitary old hulk at Portsmouth, Nelson’s Victory, seems to float there, not alone as the decaying monument of a fame incorruptible, but also as a poetic approach, softened by its picturesqueness, to the Monitors and yet mightier hulls of the European ironclads.”
—Herman Melville (1819–1891)
“The information links are like nerves that pervade and help to animate the human organism. The sensors and monitors are analogous to the human senses that put us in touch with the world. Data bases correspond to memory; the information processors perform the function of human reasoning and comprehension. Once the postmodern infrastructure is reasonably integrated, it will greatly exceed human intelligence in reach, acuity, capacity, and precision.”
—Albert Borgman, U.S. educator, author. Crossing the Postmodern Divide, ch. 4, University of Chicago Press (1992)