Principles of the anaesthetic machine

Since Boyle modified the American Gwathmay apparatus in 1917 to develop his continuous flow anaesthetic machine, much has been improved. Despite this, the basic principles and many components remain, albeit in a modernized form. Gas is still supplied to the machine from a high pressure source which is stepped down to a safe pressure supplying the breathing system. Flowmeters control gas flow and allow for adjustment of different inspired concentrations of gases. A vaporizer adds volatile anaesthetic to inspired gas to be delivered to the patient via a dedicated breathing system. Safety improvements, requirements for increased monitoring and improved technology have driven change in the anaesthetic machine. Modern anaesthetic workstations employ digital technology to deliver safe and measured anaesthesia to patients. Despite improvements in safety and reliability, routine checking of anaesthetic machines before use remains essential. The Association of Anaesthetists (formerly called the AAGBI) have developed a standardized checklist for users to ensure all components of the anaesthetic machine are functioning appropriately.