Ether came into general use after a demonstration at the Massachusetts General Hospital in Boston by William T. G. Morton in 1846. General anesthetics, administered by inhalation or intravenous injection, cause unconsciousness as well as insensibility to pain, and are used for major surgical procedures. In the past, ether was the most commonly used general anesthetic. Today, safer anesthetics include Halothane, Isoflurane, and nitrous oxide. Short-acting anesthetic agents, such as pentothal, Diprivan, and Midazolam, are generally given through intravenous or intramuscular routes.
Nitrous oxide is used for light anesthesia in minor surgical procedures and in dentistry.
Anesthetics such as Brevital may be administered rectally, primarily among children. Local anesthetics affect sensation only in the region where they are injected, and are used regularly in dentistry and minor surgery. Such anesthetics are known as regional. Muscle relaxants may be used, particularly to reduce the amount of conventional anesthetic required. Body temperatures are generally lowered in conjunction with the use of anesthetics in heart and brain surgery, reducing the body's metabolic rate so that cells are not damaged by the lack of circulating blood and reduced oxygenation.