Anaesthetic machine

An anaesthetic machine (British English) or anesthesia machine (American English) is a medical device used to generate and mix a fresh gas flow of medical gases and inhalational anaesthetic agents for the purpose of inducing and maintaining anaesthesia. The machine is commonly used together with a mechanical ventilator, breathing system, suction equipment, and patient monitoring devices; strictly speaking, the term "anaesthetic machine" refers only to the component which generates the gas flow, but modern machines usually integrate all these devices into one combined freestanding unit, which is colloquially referred to as the "anaesthetic machine" for the sake of simplicity. In the developed world, the most frequent type in use is the continuous-flow anaesthetic machine or "Boyle's machine", which is designed to provide an accurate supply of medical gases mixed with an accurate concentration of anaesthetic vapour, and to deliver this continuously to the patient at a safe pressure and flow. This is distinct from intermittent-flow anaesthetic machines, which provide gas flow only on demand when triggered by the patient's own inspiration. Simpler anaesthetic apparatus may be used in special circumstances, such as the triservice anaesthetic apparatus, a simplified anaesthesia delivery system invented for the British Defence Medical Services, which is light and portable and may be used for ventilation even when no medical gases are available. This device has unidirectional valves which suck in ambient air, which can be enriched with oxygen from a cylinder, with the help of a set of bellows. The original concept of continuous-flow machines was popularised by Boyle's anaesthetic machine, invented by the British anaesthetist Henry Boyle at St Bartholomew's Hospital in London, United Kingdom in 1917, although similar machines had been in use in France and the United States. Prior to this time, anaesthesiologists often carried all their equipment with them, but the development of heavy, bulky cylinder storage and increasingly elaborate airway equipment meant that this was no longer practical for most circumstances.