An anesthetic gas is a gas that causes temporary loss of awareness and physical sensation. Anesthetic gases cause general anesthesia, or total loss of consciousness, rather than local or regional anesthesia, which blocks sensation only in particular body parts. Anesthetic gas is often used in modern medicine, either by itself or in combination with intravenous anesthetics, to keep patients unconscious during surgery. A doctor trained to administer anesthetics is called an anesthesiologist or anesthetist. Despite being commonplace in modern medicine, the mechanism by which anesthetic gas works is still uncertain.
Most anesthetic gases are part of a group of a group of organic compounds called ethers. Most ethers in use today are also part of a subdivision of ethers called halogenated ethers, which replace at least one of the hydrogen atoms in non-halogenated ethers with atoms of one of the halogen elements and are less flammable than other ethers. The halogenated ethers most commonly used for anesthesia today are desflurane (2,2,2-trifluoro-1-fluoroethyl-difluoromethyl ether), sevoflurane (2,2,2-trifluoro-1-[trifluoromethyl]ethyl fluoromethyl ether), and isoflurane (2-chloro-2-(difluoromethoxy)-1,1,1-trifluoro-ethane). They are used either by themselves, in combination with each other, or in combination with nitrous oxide. Besides ethers, other halogenated organic compounds are also effective anesthetic gases, although these are no longer widely used for anesthesia in the developed world.
Although they are absorbed by the patient in gaseous form, ethers and other halogenated organic anesthetics can actually be stored in liquid form at room temperature. Due to their high volatility, they rapidly vaporize when not contained. A device called an anesthetic vaporizer, which is bound to an anesthesia machine, is used to administer them to patients.
Other anesthetic gases are stored in gaseous form. Nitrous oxide (N2) is an anesthetic gas, though it is not powerful enough to cause loss of consciousness on its own and is always used in combination with other gases or intravenous anesthetics. The noble gas xenon has also been introduced as a general anesthetic, though it remains very costly. Nitrogen, krypton, and argon have anesthetic effects when inhaled in a hyperbaric environment.
The first anesthetic gas used, diethyl ether (C2H5)2O), is dangerously flammable and no longer widely used now that less hazardous halogenated ethers are readily available. Other ethers that have largely fallen out of use include enflurane (2-chloro-1,1,2,-trifluoroethyl-difluoromethyl ether) and methoxyflurane ( 2,2-dichloro-1,1-difluoroethyl methyl ether). The non-ether halogenated hydrocarbons, halothane (2-bromo-2-chloro-1,1,1-trifluoroethane), chloroform (CHCl3), and trichloroethene (1,1,2-trichloroethene), were once widely used in the developed world for general anesthesia, but have fallen out of favor due to their toxicity. Some of these gases are still used for anesthesia in poorer countries where more modern anesthetic gases are not readily available or affordable.