ABSTRACT
From the title of this chapter, the reader is expected to understand what is meant by the “activity” of an inhaled “anesthetic,” yet the terms activity and anesthesia are difficult to define. When an anesthetic is described as being “active,” it is implied that varying degrees of activity may exist and that anesthetics can also be “inactive.” One situation in which inhaled anesthetics are considered to be inactive is when they are administered at relatively low concentrations (partial pressures) such that they have no obvious behavioral or physiologic effects. An example of an inactive agent might be breathing 0.79 atm nitrogen in room air at atmospheric pressure. However, when air is breathed at hyperbaric pressures greater than 3 atm, the presence of nitrogen in air produces behavioral changes in humans that include euphoria, a slowing of mental activity, and impaired neuromuscular coordination.
