inhalation anesthesia, anesthesia achieved by the inhalation of an anesthetic gas or a vapor. Although general anesthesia by inhalation has been used to permit surgical operations for over a century, the mechanism by which these anesthetics act is not completely understood. In adults, administration of an inhalation anesthetic is usually initiated during the induction phase of anesthesia after IV administration of a short-acting hypnotic drug, such as sodium pentothal, etomidate, or propofol. In pediatrics, inhalation anesthesia is often used to initiate anesthesia by using a mask induction with a nonpungent inhalational agent such as sevoflurane and nitrous oxide. The procedure may require endotracheal intubation or other methods of maintenance of airway patency and control. Among the principal inhalation anesthetics are nitrous oxide, desflurane, sevoflurane, and isoflurane.