We administer anesthetics to obtain therapeutic effects and minimize untoward side effects. Anesthetists can precisely control inhaled anesthetic concentrations by controlling end-tidal volatile anesthetic concentrations. This degree of control eliminates the need for closed-loop inhaled anesthetic systems. The low solubility of modern inhaled anesthetics adds to the stability and control of the anesthetic state; the effective inhaled concentration varies little during maintenance of anesthesia unless altered by the anesthetist. A less precise closed-loop system applies a processed electroencephalogram (EEG) to assess depth of anesthesia and enable accurate delivery of volatile and intravenous anesthetics to maintain a stable state of anesthesia.