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==Introduction==
==Introduction==
A vapouriser delivers safe and effective concentrations of anaesthetic vapour and are commonly found on the back bar of an anaesthetic machine. As most inhalation agents are stored as liquids at room temperature, there is a requirement for them to vapourised before reaching the patient. Safe concentrations are achieved by the stream of fresh gas being split as it reaches the vapouriser causing some of it to pass through the vapouriser chamber containing the saturated vapour, while the remaining gas bypasses this meaning that the vapour is diluted down making it safe for the patient to breathe.
A vapouriser delivers safe and effective concentrations of anaesthetic vapour and are commonly found on the back bar of an anaesthetic machine. As most inhalation agents are stored as liquids at room temperature, there is a requirement for them to be vapourised before reaching the patient. Safe concentrations are achieved by the stream of fresh gas being split as it reaches the vapouriser causing some of it to pass through the vapouriser chamber containing the saturated vapour, while the remaining gas bypasses this meaning that the vapour is diluted down making it safe for the patient to breathe.
*''Plenum vapourisers'' have the gas flowing through them under positive pressure wher the gas is delivered from flowmeters proximal to it on the anaesthetic machine. They are the most common type and fitted to the backbar of the machine.
*''Plenum vapourisers'' have the gas flowing through them under positive pressure where the gas is delivered from flowmeters proximal to it on the anaesthetic machine. They are the most common type and fitted to the backbar of the machine.
*''Down-over vapourisers'' have the gas flowing through them under negative pressure developed distal to it, generated by the patient's inspiration. They have low resistance to gas flow and are usually used 'in-circuit'.
*''Down-over vapourisers'' have the gas flowing through them under negative pressure developed distal to it, generated by the patient's inspiration. They have low resistance to gas flow and are usually used 'in-circuit'.
These vapourisers are used for Desflurane, as it has a very low boiling point and would not stay as a liquid in conventional vapourisers. These vapourises are electrically heated to maintain the agent chamber at a constant temperature allowing the agent to remain liquified.
These vapourisers are used for Desflurane, as it has a very low boiling point and would not stay as a liquid in conventional vapourisers. These vapourises are electrically heated to maintain the agent chamber at a constant temperature allowing the agent to remain liquified.
To prevent the incorrect agent being used in the incorrect vapouriser a ke-indexed filling system has been designed so that each agent has a specific key that will only fit in the appropriate vapouriser. Sevoflurane and desflurane are sold such that the bottles will only fit into the filler ports on the appropriate vapouriser.
To prevent the incorrect agent being used in the incorrect vapouriser a key-indexed filling system has been designed so that each agent has a specific key that will only fit in the appropriate vapouriser. Sevoflurane and desflurane are sold such that the bottles will only fit into the filler ports on the appropriate vapouriser.
==Vapouriser In-Circuit Machines==
==Vapouriser In-Circuit Machines==
Komesaroff and Stephens' anaesthetic machines are both examples of a vapouriser in-circuit machine. They are essentially a circle breathing system with one or more draw-over vapouriser within the circuit. They are economical due to very low required gas flows but disadvantages include possible overdosing and performance of vapouriser may be contaminated by water vapour.
Komesaroff and Stephens' anaesthetic machines are both examples of a vapouriser in-circuit machine. They are essentially a circle breathing system with one or more draw-over vapourisers within the circuit. They are economical due to very low required gas flows but disadvantages include possible overdosing and performance of vapouriser may be contaminated by water vapour.