Anesthetic depth: the undefinable

With many modern anesthetic drugs and combinations, the traditional signs of anesthetic depth as a continuum of increasing depression are often incorrect. The concept of "adequate anesthetic depth" is difficult to define because it depends on the end points chosen to define "adequate." Because both central nervous system excitant and depressant drugs can induce a stage of anesthesia, it is vital that those using these agents be keenly aware of the specific type of anesthetic agent or agents being used, and their effects.