Until recently, anesthesiol ogist lacked the ability tomonitor the effects of anesthetics on the brain in terms of"depth" or "adequacy” of ane sth esi a. it is bel iev ed tha tgen era l ane sth eti cs blo ck consciousne ss by depres singthe central nervous system, electrical activity of thecerebral cortex can be measured using theelectro encephal ogram (EEG), some compone nts of theEEG are rel ate d to ade qua cy of ane sth esi a. BIS is thefir st technology approved by the U.S. Food and DrugAdministration (FDA) for marketi ng as an EEG-basedmonito r for anesthet ic effect. Entropy is another EEG –based monitor.