<P> Drugs given to induce general anaesthesia can be either as gases or vapours (inhalational anaesthetics), or as injections (intravenous anaesthetics or even intramuscular). All of these agents share the property of being quite hydrophobic (i.e., as liquids, they are not freely miscible--or mixable--in water, and as gases they dissolve in oils better than in water). It is possible to deliver anaesthesia solely by inhalation or injection, but most commonly the two forms are combined, with an injection given to induce anaesthesia and a gas used to maintain it . </P> <P> Inhalational anaesthetic substances are either volatile liquids or gases, and are usually delivered using an anaesthesia machine . An anaesthesia machine allows composing a mixture of oxygen, anaesthetics and ambient air, delivering it to the patient and monitoring patient and machine parameters . Liquid anaesthetics are vapourised in the machine . </P> <P> Many compounds have been used for inhalation anaesthesia, but only a few are still in widespread use . Desflurane, isoflurane and sevoflurane are the most widely used volatile anaesthetics today . They are often combined with nitrous oxide . Older, less popular, volatile anaesthetics, include halothane, enflurane, and methoxyflurane . Researchers are also actively exploring the use of xenon as an anaesthetic . </P> <P> Injectable anaesthetics are used for the induction and maintenance of a state of unconsciousness . Anaesthetists prefer to use intravenous injections, as they are faster, generally less painful and more reliable than intramuscular or subcutaneous injections . Among the most widely used drugs are: </P>

What type of gas is used for anesthesia
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