Anaesthetics

Abstract

A typical general anaesthetic consists of a premedication, an induction and an inhalational anaesthetic. Premedication is given to the patient in the ward before being brought to the operating theatre. Anaesthesia is induced by the anaesthetist giving a slow intravenous injection of a short acting anaesthetic agent such as thiopental or methohexitone. This induces a rapid loss of consciousness. The anaesthetic is then maintained by administering a mixture of anaesthetic gases, the active agent being one of the halogenated gases such as halothane or methoxyflurane. The carrier gases include oxygen and nitrous oxide, which is itself a weak anaesthetic. The gas mixture can be administered by face mask or via an intratracheal tube. The patient may either be allowed to breathe the gas mixture spontaneously or artificial ventilation can be used, in which case it is usual to paralyse all the patient’s voluntary muscles with a muscle relaxant.