From wall to patient: the anatomy of the anaesthetic machine

anaesthetic machine breathing circuit ventilator Oct 22, 2026

The anaesthetic machine is something we work alongside every day in perianaesthesia practice, but have you ever stopped to think about what happens between the wall gas outlet and the patient? Behind the familiar screens, tubing and controls is a carefully designed system responsible for delivering oxygen, anaesthetic gases and ventilation.

Understanding how these components connect helps us recognise why machine checks, alarms and circuit integrity are so important.

The journey begins with medical gases entering the machine through the pipeline supply or reserve cylinders. Pressure is regulated, gas flow is controlled, and volatile anaesthetic agents may be added before the mixture reaches the breathing system.

🔹 Gas supply and pressure regulation. Pipeline gases provide the usual supply, while reserve cylinders offer an alternative if the pipeline fails.

🔹 Flow controls and vapourisers. These regulate fresh gas delivery and, when required, introduce a controlled concentration of volatile anaesthetic.

🔹 Breathing circuit and ventilator. These support gas delivery and ventilation, with one-way valves directing flow through the circle system.

🔹 Carbon dioxide absorption. The absorber removes carbon dioxide from exhaled gases, allowing appropriate gas rebreathing.

🔹 Scavenging and safety systems. These help remove waste anaesthetic gases and provide important warnings when equipment problems occur.

For perianaesthesia nurses, understanding this pathway adds meaning to routine equipment checks. ANZCA recommends checks at the beginning of each anaesthetic list and before each patient, with the anaesthetist retaining responsibility for the relevant checks.

The clinical takeaway? Knowing how gases travel from wall to patient helps us recognise abnormalities, communicate concerns and support safe anaesthetic care.

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References

Hill, N.E. and Horn, D.B. (2022). Anesthesia Machine. StatPearls Publishing.

Australian and New Zealand College of Anaesthetists (ANZCA) (2026). PG31 Guideline on checking anaesthesia delivery systems 2026. ANZCA. Pilot document.

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