Stages of Anesthesia

Abstract

Clinically and encephalographically distinct, definable stages are passed through on the way from induction to progressive deepening of anesthesia, and again in reverse order during termination of anesthesia. These stages were defined by Guedel in 1920 (according to clinical parameters, giving stages I–IV) and by Kugler in 1966 (according to EEG changes, giving stages A–F). The stages of anesthesia include all levels of consciousness from alertness through analgesia to deep coma with collapse of all vegetative functions. The sequence is analgesia, excitation, light, moderate, and deep anesthesia. At this point the tolerance limit of the administered substance has been reached. Additional application of anesthetic will induce intoxication with total cerebral depression. The correlation between clinical stages of anesthesia and EEG findings will be demonstrated by tables and selected examples.