Anesthesia and Central Nervous System
Although anesthetics in general affect both function and metabolism of the brain the effects are quite variable. Some anesthetics (e.g. barbiturates) lead to an orderly progression of symptoms, starting with an initial excitation (stage I) progressing to delirium, sometimes accompanied by hallucinations and a cataleptic behavior (stage II), and ending in the unconsciousness of surgical anesthesia (stage III). However, other anesthetics like nitrous oxide and ketamine never cause stage III anesthesia and still others (e.g. enflurane) increase excitability and elicit seizures.