This chapter gives an overview of the basic components of anaesthetic system breathing equipment. It begins by covering pipeline gas supplies and the physics of cylinder storage of gas. This then moves on to the anaesthetic breathing systems and Mapleson classification of circuits, a very popular and core exam topic. The chapter then focusses on the anaesthetic breathing machines, low flow circle systems and their core components which includes scavenging, vaporisers, soda lime and carbon dioxide absorption.

The anaesthetic machine is designed to enable oxygenation, safe delivery of both gases and volatile anaesthetic agents and appropriate ventilation. Modern machines are complex pieces of equipment dependent on electronic hardware and software. Many incorporate electronic monitoring systems for both the patient and the gas delivery. Breathing systems and ventilators may be included to form a ‘workstation’. Familiarity with the anaesthetic machine is fundamental for safe practice. It must be checked before every operating list.

Gas supply is usually via pipelines drawn from a central supply or from cylinders. Pressure and flow of gases to the patient are regulated by valves and flowmeters. The concentration of volatile agents is controlled by individual vaporisers. Anaesthetic gas scavenging systems are designed to safely remove anaesthetic waste.

Anaesthetic breathing systems or circuits consist of several components: fresh gas, inspiratory and expiratory limbs, a pressure limiting valve and a reservoir bag. They may also have a carbon dioxide absorber and unidirectional valves. They are classified as either circle systems or semi-closed rebreathing systems. Ventilators can be considered as constant or non-constant generators of pressure or flow. Both are described in detail.

The primary purpose of the anaesthetic machine is to deliver anaesthetic gases and volatile agents safely to the patient - helping to maintain a suitable level of consciousness and analgesia for surgery. It is vital that any clinician checking and using an anaesthetic machine is familiar with the type of machine they are intending to use and possess a detailed knowledge of how it operates. Machines must be rigorously checked and tested by a suitably trained person before use and a breathing circuit check should take place between each patient. This chapter is an introduction to the anaesthetic machine, highlighting the main components and features that are essential to maintaining user and patient safety.